Re: [PATCH v2 03/23] KVM: SVM: Process ICR on AVIC IPI delivery failure due to invalid target

Paolo Bonzini
2022-09-05T22:00:34Z

On 9/3/22 02:22, Sean Christopherson wrote:
> Emulate ICR writes on AVIC IPI failures due to invalid targets using the
> same logic as failures due to invalid types. AVIC acceleration fails if
> _any_ of the targets are invalid, and crucially VM-Exits before sending
> IPIs to targets that _are_ valid. In logical mode, the destination is a
> bitmap, i.e. a single IPI can target multiple logical IDs. Doing nothing
> causes KVM to drop IPIs if at least one target is valid and at least one
> target is invalid.
>
> Fixes: 18f40c53e10f ("svm: Add VMEXIT handlers for AVIC")
> Cc: stable@vger.kernel.org
> Signed-off-by: Sean Christopherson <seanjc@google.com>
> Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>
> ---
> arch/x86/kvm/svm/avic.c | 16 +++++++++-------
> 1 file changed, 9 insertions(+), 7 deletions(-)
>
> diff --git a/arch/x86/kvm/svm/avic.c b/arch/x86/kvm/svm/avic.c
> index 4fbef2af1efc..6a3d225eb02c 100644
> --- a/arch/x86/kvm/svm/avic.c
> +++ b/arch/x86/kvm/svm/avic.c
> @@ -502,14 +502,18 @@ int avic_incomplete_ipi_interception(struct kvm_vcpu *vcpu)
> trace_kvm_avic_incomplete_ipi(vcpu->vcpu_id, icrh, icrl, id, index);
>
> switch (id) {
> + case AVIC_IPI_FAILURE_INVALID_TARGET:
> case AVIC_IPI_FAILURE_INVALID_INT_TYPE:
> /*
> * Emulate IPIs that are not handled by AVIC hardware, which
> - * only virtualizes Fixed, Edge-Triggered INTRs. The exit is
> - * a trap, e.g. ICR holds the correct value and RIP has been
> - * advanced, KVM is responsible only for emulating the IPI.
> - * Sadly, hardware may sometimes leave the BUSY flag set, in
> - * which case KVM needs to emulate the ICR write as well in
> + * only virtualizes Fixed, Edge-Triggered INTRs, and falls over
> + * if _any_ targets are invalid, e.g. if the logical mode mask
> + * is a superset of running vCPUs.
> + *
> + * The exit is a trap, e.g. ICR holds the correct value and RIP
> + * has been advanced, KVM is responsible only for emulating the
> + * IPI. Sadly, hardware may sometimes leave the BUSY flag set,
> + * in which case KVM needs to emulate the ICR write as well in
> * order to clear the BUSY flag.
> */
> if (icrl & APIC_ICR_BUSY)
> @@ -525,8 +529,6 @@ int avic_incomplete_ipi_interception(struct kvm_vcpu *vcpu)
> */
> avic_kick_target_vcpus(vcpu->kvm, apic, icrl, icrh, index);
> break;
> - case AVIC_IPI_FAILURE_INVALID_TARGET:
> - break;
> case AVIC_IPI_FAILURE_INVALID_BACKING_PAGE:
> WARN_ONCE(1, "Invalid backing page\n");
> break;

Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>