On 07/03/2018 16:35, Sean Christopherson wrote:
> On Wed, 2018-03-07 at 16:19 +0100, Paolo Bonzini wrote:
>> On 06/03/2018 21:58, Sean Christopherson wrote:
>>>
>>> Fast emulation of processor I/O for IN was disabled on x86 (both VMX
>>> and SVM) some years ago due to a buggy implementation. The addition
>>> of kvm_fast_pio_in(), used by SVM, re-introduced (functional!) fast
>>> emulation of IN. Piggyback SVM's work and use kvm_fast_pio_in() on
>>> VMX instead of performing full emulation of IN.
>>>
>>> Signed-off-by: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>
>> There's a little code duplication that would be nice to avoid, moving
>> kvm_skip_emulated_instruction to kvm_fast_pio_{in,out}. Otherwise,
>
> What about adding kvm_fast_pio() to also avoid duplication of branching
> on 'in' versus 'out'? That seems worthy of a v2.
If you would like to do that for a v2, that makes sense as well, indeed.
Paolo
>>
>> Reviewed-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
>>
>> Paolo
>>
>>>
>>> ---
>>> arch/x86/kvm/vmx.c | 9 ++++++---
>>> 1 file changed, 6 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
>>> index 051dab74e4e9..c8a8391e95e5 100644
>>> --- a/arch/x86/kvm/vmx.c
>>> +++ b/arch/x86/kvm/vmx.c
>>> @@ -6231,15 +6231,15 @@ static int handle_io(struct kvm_vcpu *vcpu)
>>>
>>> exit_qualification = vmcs_readl(EXIT_QUALIFICATION);
>>> string = (exit_qualification & 16) != 0;
>>> - in = (exit_qualification & 8) != 0;
>>>
>>> ++vcpu->stat.io_exits;
>>>
>>> - if (string || in)
>>> + if (string)
>>> return emulate_instruction(vcpu, 0) == EMULATE_DONE;
>>>
>>> port = exit_qualification >> 16;
>>> size = (exit_qualification & 7) + 1;
>>> + in = (exit_qualification & 8) != 0;
>>>
>>> ret = kvm_skip_emulated_instruction(vcpu);
>>>
>>> @@ -6247,7 +6247,10 @@ static int handle_io(struct kvm_vcpu *vcpu)
>>> * TODO: we might be squashing a KVM_GUESTDBG_SINGLESTEP-triggered
>>> * KVM_EXIT_DEBUG here.
>>> */
>>> - return kvm_fast_pio_out(vcpu, size, port) && ret;
>>> + if (in)
>>> + return kvm_fast_pio_in(vcpu, size, port) && ret;
>>> + else
>>> + return kvm_fast_pio_out(vcpu, size, port) && ret;
>>> }
>>>
>>> static void
>>>
