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KVM: SVM: Document that vCPU ID == APIC ID in AVIC kick fastpatch

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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@google.com>
Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>
Message-Id: <20230106011306.85230-16-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Sean Christopherson 2023-01-06 01:12:48 +00:00 committed by Paolo Bonzini
parent f9829c9076
commit 8578e4512d
1 changed files with 7 additions and 3 deletions
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10
arch/x86/kvm/svm/avic.c
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@ -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;