Re: [PATCH 3/3] KVM: x86: Don't re-execute instruction when not passing CR2 value

[Liran Alon <LIRAN.ALON@ORACLE.COM>]

On 06/11/17 11:21, Paolo Bonzini wrote:
> On 05/11/2017 15:21, Liran Alon wrote:
>> From: Liran Alon <liran.alon@ravellosystems.com>
>>
>> In case of instruction-decode failure or emulation failure,
>> x86_emulate_instruction() will call reexecute_instruction() which will
>> attempt to use the cr2 value passed to x86_emulate_instruction().
>> However, when x86_emulate_instruction() is called from
>> emulate_instruction(), cr2 is not passed (passed as 0) and therefore
>> it doesn't make sense to execute reexecute_instruction() logic at all.
>>
>> Fixes: 51d8b66199e9 ("KVM: cleanup emulate_instruction")
>>
>> Signed-off-by: Liran Alon <liran.alon@oracle.com>
>> Reviewed-by: Nikita Leshenko <nikita.leshchenko@oracle.com>
>> Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
>> Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
>> ---
>>   arch/x86/include/asm/kvm_host.h | 3 ++-
>>   1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
>> index c73e493adf07..bc1347949cef 100644
>> --- a/arch/x86/include/asm/kvm_host.h
>> +++ b/arch/x86/include/asm/kvm_host.h
>> @@ -1156,7 +1156,8 @@ int x86_emulate_instruction(struct kvm_vcpu *vcpu, unsigned long cr2,
>>   static inline int emulate_instruction(struct kvm_vcpu *vcpu,
>>   			int emulation_type)
>>   {
>> -	return x86_emulate_instruction(vcpu, 0, emulation_type, NULL, 0);
>> +	return x86_emulate_instruction(vcpu, 0,
>> +			emulation_type | EMULTYPE_NO_REEXECUTE, NULL, 0);
>>   }
>>
>>   void kvm_enable_efer_bits(u64);
>>
>
> You can remove EMULTYPE_NO_REEXECUTE from handle_invalid_guest_state now.
Nice catch. Will remove it in next version of this commit. Thanks.
>
> Thanks,
>
> Paolo
>