syzbot

uvm_fault(fffffd806c219560,20080000,0,1) at uvm_fault+0x112 sys/uvm/uvm_fault.c:600
kpageflttrap(ffff80002a0bfe20,20080000) at kpageflttrap+0x2d0 sys/arch/amd64/amd64/trap.c:279
kerntrap(ffff80002a0bfe20) at kerntrap+0x14a sys/arch/amd64/amd64/trap.c:332
alltraps_kern_meltdown() at alltraps_kern_meltdown+0x7b
_copyin() at _copyin+0x57
syscall(ffff80002a0c0270) at syscall+0xbb6 mi_syscall sys/sys/syscall_mi.h:179 [inline]
syscall(ffff80002a0c0270) at syscall+0xbb6 sys/arch/amd64/amd64/trap.c:577
Xsyscall() at Xsyscall+0x128
end of kernel
end trace frame: 0xde3235647e0, count: -23
ddb{0}> machine ddbcpu 1
Stopped at      savectx+0xae:   movl    $0,%gs:0x680
savectx() at savectx+0xae
end of kernel
end trace frame: 0xde2ec2c8150, count: 14
ddb{1}> trace
savectx() at savectx+0xae
end of kernel
end trace frame: 0xde2ec2c8150, count: -1