syzbot

uvm_fault(fffffd806c136540,20000000,0,2) at uvm_fault+0x112 sys/uvm/uvm_fault.c:600
kpageflttrap(ffff80002a084610,2000029c) at kpageflttrap+0x2d0 sys/arch/amd64/amd64/trap.c:279
kerntrap(ffff80002a084610) at kerntrap+0x14a sys/arch/amd64/amd64/trap.c:332
alltraps_kern_meltdown() at alltraps_kern_meltdown+0x7b
copyout() at copyout+0x62
kern_sysctl(ffff80002a084994,5,20000100,ffff80002a0849c8,0,37,977f9bf584a06a94) at kern_sysctl+0x320 sys/kern/kern_sysctl.c:500
sys_sysctl(ffff8000371c87c0,ffff80002a084b00,ffff80002a084a50) at sys_sysctl+0x422
syscall(ffff80002a084b00) at syscall+0xbb6 mi_syscall sys/sys/syscall_mi.h:179 [inline]
syscall(ffff80002a084b00) at syscall+0xbb6 sys/arch/amd64/amd64/trap.c:577
Xsyscall() at Xsyscall+0x128
end of kernel
end trace frame: 0x891b4c45f10, count: -24
ddb{0}> machine ddbcpu 1
Stopped at      savectx+0xae:   movl    $0,%gs:0x680
savectx() at savectx+0xae
end of kernel
end trace frame: 0x891c2954c40, count: 14
ddb{1}> trace
savectx() at savectx+0xae
end of kernel
end trace frame: 0x891c2954c40, count: -1