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

[Paolo Bonzini <pbonzini@redhat.com>]

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>