Commit 8578e451 authored by Sean Christopherson's avatar Sean Christopherson Committed by Paolo Bonzini
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KVM: SVM: Document that vCPU ID == APIC ID in AVIC kick fastpatch 



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: default avatarSean Christopherson <seanjc@google.com>
Reviewed-by: default avatarMaxim Levitsky <mlevitsk@redhat.com>
Message-Id: <20230106011306.85230-16-seanjc@google.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent f9829c90

arch/x86/kvm/svm/avic.c

+7 −3
Original line number Diff line number Diff line
@@ -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;