Re: [PATCH v2 04/23] KVM: x86: Inhibit AVIC SPTEs if any vCPU enables x2APIC

[Suthikulpanit, Suravee]

Sean

On 9/14/2022 2:39 AM, Sean Christopherson wrote:
> > > diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
> > > index 38e9b8e5278c..d956cd37908e 100644
> > > --- a/arch/x86/kvm/lapic.c
> > > +++ b/arch/x86/kvm/lapic.c
> > > @@ -2394,8 +2394,10 @@ void kvm_lapic_set_base(struct kvm_vcpu *vcpu, u64 value)
> > >    		}
> > >    	}
> > > -	if (((old_value ^ value) & X2APIC_ENABLE) && (value & X2APIC_ENABLE))
> > > +	if (((old_value ^ value) & X2APIC_ENABLE) && (value & X2APIC_ENABLE)) {
> > >    		kvm_apic_set_x2apic_id(apic, vcpu->vcpu_id);
> > > +		kvm_set_apicv_inhibit(vcpu->kvm, APICV_INHIBIT_REASON_X2APIC);
> > > +	}
> > .... Here, since we do not want to inhibit APICV/AVIC on system that can
> > support x2AVIC, this should be set in the vendor-specific call-back
> > function, where appropriate checks can be made.
> No, again the intent is to inhibit only the MMIO page.  The x2APIC inhibit is
> ignored when determining whether or not APICv is inhibited, but is included when
> checking if the memslot is inhibited.
>
> bool kvm_apicv_memslot_activated(struct kvm *kvm)
> {
> 	return (READ_ONCE(kvm->arch.apicv_inhibit_reasons) == 0);
> }
>
> static unsigned long kvm_apicv_get_inhibit_reasons(struct kvm *kvm)
> {
> 	/*
> 	 * x2APIC only needs to "inhibit" the MMIO region, all other aspects of
> 	 * APICv can continue to be utilized.
> 	 */
> 	return READ_ONCE(kvm->arch.apicv_inhibit_reasons) & ~APICV_INHIBIT_REASON_X2APIC;

Also, this should be:

return READ_ONCE(kvm->arch.apicv_inhibit_reasons) & ~(1UL << 
APICV_INHIBIT_REASON_X2APIC);

Suravee