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). Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx> Reviewed-by: Maxim Levitsky <mlevitsk@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 605c36569ddf..40a1ea21074d 100644 --- a/arch/x86/kvm/svm/avic.c +++ b/arch/x86/kvm/svm/avic.c @@ -368,8 +368,8 @@ 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)) @@ -397,7 +397,7 @@ 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; @@ -406,9 +406,13 @@ 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; -- 2.38.0.rc1.362.ged0d419d3c-goog
