lkml.org 
[lkml]   [2022]   [Sep]   [30]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    Patch in this message
    /
    Date
    Subject[PATCH v4 16/32] KVM: SVM: Document that vCPU ID == APIC ID in AVIC kick fastpatch
    From
    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>
    ---
    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
    \
     
     \ /
      Last update: 2022-10-01 03:02    [W:3.199 / U:0.684 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site