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SubjectRe: [PATCH 5/5] KVM: VMX: Handle RFLAGS.TF in skip_emulated_instruction
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On 28/11/2016 17:13, Kyle Huey wrote:
> On Mon, Nov 28, 2016 at 3:42 AM, Paolo Bonzini <pbonzini@redhat.com> wrote:
>> This code is pretty much the same as kvm_vcpu_check_singlestep. Let's
>> not duplicate the code and implement skip_emulated_instruction can be
>> implemented in x86.c, like
>>
>> unsigned long rflags = kvm_x86_ops->get_rflags(vcpu);
>> int r = EMULATE_DONE;
>>
>> /* This would be the no_trap variant */
>> kvm_x86_ops->skip_emulated_instruction(vcpu);
>> kvm_vcpu_check_singlestep(vcpu, rflags, &r);
>> return r == EMULATE_DONE;
>>
>> (because x86.c/vmx.c/svm.c are separate modules, when moving the function
>> to x86.c you should rename it to kvm_skip_emulated_instruction).
>>
>> Paolo
>
> They're not exactly the same. For some reason I don't understand
> kvm_vcpu_check_singlestep clears the trap flag. Perhaps that is also
> a bug?

The Intel manual says "The processor clears the TF flag before calling
the exception handler" (17.3.1.4), so I think you should do it too.

Paolo

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