On Thu, Dec 12, 2024 at 10:30:10AM +0000, David Woodhouse wrote:
> No, definitely not expected. Thanks for the report. I'll see if I can
> reproduce it; please could you share your kernel .config?

Attached.

> Please could you also confirm that it still occurs if you don't use
> systemctl; for speed of testing I have mostly been booting my test
> kernel with no actual root file system; just an initrd which does
> 'kexec -f' immediately.

Yes, it appears to reproduce with just 'kexec -e' after 'kexec -l'.

> Since you are running in QEMU, if you can reproduce with this patch to
> QEMU itself which should dump the CPU state on a triple-fault, it would
> be very useful please:
> 
> --- a/accel/kvm/kvm-all.c
> +++ b/accel/kvm/kvm-all.c
> @@ -3133,6 +3133,7 @@ int kvm_cpu_exec(CPUState *cpu)
>              ret = EXCP_INTERRUPT;
>              break;
>          case KVM_EXIT_SHUTDOWN:
> +            cpu_dump_state(cpu, stderr, CPU_DUMP_CODE);
>              qemu_system_reset_request(SHUTDOWN_CAUSE_GUEST_RESET);
>              ret = EXCP_INTERRUPT;
>              break;
> 
> If you get output from that, please also send the output of 'objdump -S
> arch/x86/kernel/relocate_kernel_64.o' to help interpret it.

Here is the output that I see with that patch applied when rebooting via
'systemctl kexec':

RAX=000000010c070001 RBX=0000000000000000 RCX=0000000000000000 RDX=000000047fffb1a0
RSI=000000011c444000 RDI=000000011c450002 RBP=ff1cd0424d6e8c00 RSP=ff4178d5c5aebc60
R8 =0000000000000000 R9 =000000011c446000 R10=ffffffff909f3e00 R11=0000000000000003
R12=0000000000000000 R13=0000000000000001 R14=00000000fee1dead R15=0000000000000000
RIP=ff1cd0425c44401c RFL=00010002 [-------] CPL=0 II=0 A20=1 SMM=0 HLT=0
ES =0018 0000000000000000 ffffffff 00c09300 DPL=0 DS   [-WA]
CS =0010 0000000000000000 ffffffff 00a09b00 DPL=0 CS64 [-RA]
SS =0018 0000000000000000 ffffffff 00c09300 DPL=0 DS   [-WA]
DS =0018 0000000000000000 ffffffff 00c09300 DPL=0 DS   [-WA]
FS =0018 0000000000000000 ffffffff 00c09300 DPL=0 DS   [-WA]
GS =0018 0000000000000000 ffffffff 00c09300 DPL=0 DS   [-WA]
LDT=0000 0000000000000000 ffffffff 00c00000
TR =0040 fffffe043fedb000 00004087 00008b00 DPL=0 TSS64-busy
GDT=     0000000000000000 00000000
IDT=     0000000000000000 00000000
CR0=80050033 CR2=ff1cd0425c4441de CR3=000000011c446000 CR4=00771ef0
DR0=0000000000000000 DR1=0000000000000000 DR2=0000000000000000 DR3=0000000000000000
DR6=00000000fffe0ff0 DR7=0000000000000400
EFER=0000000000000d01
Code=41 57 9c 6a 00 9d 0f 20 d8 4c 8b 0d ee 01 00 00 41 0f 22 d9 <48> 89 25 bb 01 00 00 48 89 05 c4 01 00 00 0f 20 c0 48 89 05 b2 01 00 00 41 0f 20 e5 4c 89

And with just 'kexec -e':

RAX=0000000112280006 RBX=0000000000000000 RCX=0000000000000000 RDX=000000047fffb1a0
RSI=00000001076d1000 RDI=000000010ca2b002 RBP=ff1d6a35cd14bc00 RSP=ff541c6303a0fb50
R8 =0000000000000000 R9 =000000010bc34000 R10=ffffffff841f3e00 R11=0000000000000003
R12=0000000000000000 R13=0000000000000001 R14=00000000fee1dead R15=0000000000000000
RIP=ff1d6a35c76d101c RFL=00010002 [-------] CPL=0 II=0 A20=1 SMM=0 HLT=0
ES =0018 0000000000000000 ffffffff 00c09300 DPL=0 DS   [-WA]
CS =0010 0000000000000000 ffffffff 00a09b00 DPL=0 CS64 [-RA]
SS =0018 0000000000000000 ffffffff 00c09300 DPL=0 DS   [-WA]
DS =0018 0000000000000000 ffffffff 00c09300 DPL=0 DS   [-WA]
FS =0018 0000000000000000 ffffffff 00c09300 DPL=0 DS   [-WA]
GS =0018 0000000000000000 ffffffff 00c09300 DPL=0 DS   [-WA]
LDT=0000 0000000000000000 ffffffff 00c00000
TR =0040 fffffe54abf61000 00004087 00008b00 DPL=0 TSS64-busy
GDT=     0000000000000000 00000000
IDT=     0000000000000000 00000000
CR0=80050033 CR2=ff1d6a35c76d11de CR3=000000010bc34000 CR4=00771ef0
DR0=0000000000000000 DR1=0000000000000000 DR2=0000000000000000 DR3=0000000000000000
DR6=00000000fffe0ff0 DR7=0000000000000400
EFER=0000000000000d01
Code=41 57 9c 6a 00 9d 0f 20 d8 4c 8b 0d ee 01 00 00 41 0f 22 d9 <48> 89 25 bb 01 00 00 48 89 05 c4 01 00 00 0f 20 c0 48 89 05 b2 01 00 00 41 0f 20 e5 4c 89

I have attached the output of 'objdump -S'. Please let me know if you
would like any other information or testing.

Cheers,
Nathan