Re: [PATCH v3 6/8] KVM-HV: Add flush_on_enter before guest enter

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On Fri, Aug 03, 2012 at 11:07:13AM +0530, Nikunj A Dadhania wrote:
> On Thu, 2 Aug 2012 17:16:41 -0300, Marcelo Tosatti <mtosatti@xxxxxxxxxx> wrote:
> > On Thu, Aug 02, 2012 at 05:14:02PM -0300, Marcelo Tosatti wrote:
> > > On Tue, Jul 31, 2012 at 04:19:02PM +0530, Nikunj A. Dadhania wrote:
> > > > From: Nikunj A. Dadhania <nikunj@xxxxxxxxxxxxxxxxxx>
> > > >  
> > > >  static void kvm_set_vcpu_state(struct kvm_vcpu *vcpu)
> > > >  {
> > > > @@ -1584,7 +1573,8 @@ static void kvm_set_vcpu_state(struct kvm_vcpu *vcpu)
> > > >  	kaddr = kmap_atomic(vcpu->arch.v_state.vs_page);
> > > >  	kaddr += vcpu->arch.v_state.vs_offset;
> > > >  	vs = kaddr;
> > > > -	kvm_set_atomic(&vs->state, 0, 1 << KVM_VCPU_STATE_IN_GUEST_MODE);
> > > > +	if (xchg(&vs->state, VS_IN_GUEST) == VS_SHOULD_FLUSH)
> > > > +		kvm_x86_ops->tlb_flush(vcpu);
> > > >  	kunmap_atomic(kaddr);
> > > >  }
> > > >  
> > > > @@ -1600,7 +1590,8 @@ static void kvm_clear_vcpu_state(struct kvm_vcpu *vcpu)
> > > >  	kaddr = kmap_atomic(vcpu->arch.v_state.vs_page);
> > > >  	kaddr += vcpu->arch.v_state.vs_offset;
> > > >  	vs = kaddr;
> > > > -	kvm_set_atomic(&vs->state, 1 << KVM_VCPU_STATE_IN_GUEST_MODE, 0);
> > > > +	if (xchg(&vs->state, VS_NOT_IN_GUEST) == VS_SHOULD_FLUSH)
> > > > +		kvm_x86_ops->tlb_flush(vcpu);
> > > >  	kunmap_atomic(kaddr);
> > > >  }
> > > 
> > > Nevermind the early comment (the other comments on that message are
> > > valid).
> I assume the above is related to kvm_set_atomic comment in the [3/8]

Yes.

> > Ah, so the pseucode mentions flush-on-exit because we can be clearing 
> > the flag on xchg. Setting KVM_REQ_TLB_FLUSH instead should be enough
> > (please verify).
> > 
> Yes, that will work while exiting. 
> 
> In the vm_enter case, we need to do a kvm_x86_ops->tlb_flush(vcpu), as
> we have already passed the phase of checking the request.

Yes.

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