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

Suthikulpanit, Suravee
2022-09-14T17:41:39Z

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