On Wed, 2022-08-31 at 00:34 +0000, Sean Christopherson wrote: > Document that AVIC is inhibited if any vCPU's APIC ID diverges from its > vCPU ID, i.e. that there's no need to check for a destination match in > the AVIC kick fast path. > > Opportunistically tweak comments to remove "guest bug", as that suggests > KVM is punting on error handling, which is not the case. Targeting a > non-existent vCPU or no vCPUs _may_ be a guest software bug, but whether > or not it's a guest bug is irrelevant. Such behavior is architecturally > legal and thus needs to faithfully emulated by KVM (and it is). I don't want to pick a fight, but personally these things *are* guest bugs / improper usage of APIC, and I don't think it is wrong to document them as such. Reviewed-by: Maxim Levitsky <mlevitsk@xxxxxxxxxx> > > Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx> > --- > arch/x86/kvm/svm/avic.c | 10 +++++++--- > 1 file changed, 7 insertions(+), 3 deletions(-) > > diff --git a/arch/x86/kvm/svm/avic.c b/arch/x86/kvm/svm/avic.c > index 05a1cde8175c..3959d4766911 100644 > --- a/arch/x86/kvm/svm/avic.c > +++ b/arch/x86/kvm/svm/avic.c > @@ -380,8 +380,8 @@ static int avic_kick_target_vcpus_fast(struct kvm *kvm, struct kvm_lapic *source > cluster = (dest >> 4) << 2; > } > > + /* Nothing to do if there are no destinations in the cluster. */ > if (unlikely(!bitmap)) > - /* guest bug: nobody to send the logical interrupt to */ > return 0; > > if (!is_power_of_2(bitmap)) > @@ -399,7 +399,7 @@ static int avic_kick_target_vcpus_fast(struct kvm *kvm, struct kvm_lapic *source > if (WARN_ON_ONCE(index != logid_index)) > return -EINVAL; > > - /* guest bug: non existing/reserved logical destination */ > + /* Nothing to do if the logical destination is invalid. */ > if (unlikely(!(logid_entry & AVIC_LOGICAL_ID_ENTRY_VALID_MASK))) > return 0; > > @@ -418,9 +418,13 @@ static int avic_kick_target_vcpus_fast(struct kvm *kvm, struct kvm_lapic *source > } > } > > + /* > + * KVM inhibits AVIC if any vCPU ID diverges from the vCPUs APIC ID, > + * i.e. APIC ID == vCPU ID. Once again, nothing to do if the target > + * vCPU doesn't exist. > + */ > target_vcpu = kvm_get_vcpu_by_id(kvm, l1_physical_id); > if (unlikely(!target_vcpu)) > - /* guest bug: non existing vCPU is a target of this IPI*/ > return 0; > > target_vcpu->arch.apic->irr_pending = true;
