Re: kvm: emulation failure

[Sheng Yang <sheng@linux.intel.com>]

On Saturday 20 June 2009 03:23:40 Ram Pai wrote:
> I see this problem with a x86 sles10 guest running on x86_64 intel host.
> If the guest is reset abruptly and rebooted, some where
> before grub sequence it hangs and the following message is seen in the
> logs
>
> emulation failed (pagetable) rip 7ed5 66 60 ac 20.
>
> I located this instruction sequence in isolinux.bin on the iso ;if that
> is relevant.
>
>
> I did some analysis and find that there is an ept violation, which is
> handled and then the next instruction '66 60' is attempted to decode
> and emulate. But decode fails. kvm continues loops in the kernel
> in __vcpu_run().
>
> the code path is
>
> kvm_run() -> __vcpu_run() -> vcpu_enter_guest() -> kvm_handle_exit() ->
> handle_ept_violation() -> kvm_mmu_page_fault() -> emulate_instruction() ->
> x86_decode_insn()
>

Hi Ram

Seems KVM failed to emulate a unknown instruction. 

00000000  6660              pushad
00000002  AC                lodsb

And PUSHAD have not implemented in x86_emulate.c.

But I am a little curious about why this code path was only triggered when 
reset. Maybe other issue exists.

-- 
regards
Yang, Sheng

>
> Any insights here on how to fix the problem is appreciated. And if a fix
> already exists even better :)
>
> thanks,
> RP
>
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