Re: [PATCH 3/4] KVM: x86: check PIR even for vCPUs with disabled APICv

David Matlack
2021-11-29T23:39:17Z

On Mon, Nov 22, 2021 at 07:43:10PM -0500, Paolo Bonzini wrote:
> The IRTE for an assigned device can trigger a POSTED_INTR_VECTOR even
> if APICv is disabled on the vCPU that receives it. In that case, the
> interrupt will just cause a vmexit and leave the ON bit set together
> with the PIR bit corresponding to the interrupt.
>
> Right now, the interrupt would not be delivered until APICv is re-enabled.
> However, fixing this is just a matter of always doing the PIR->IRR
> synchronization, even if the vCPU has temporarily disabled APICv.
>
> This is not a problem for performance, or if anything it is an
> improvement. First, in the common case where vcpu->arch.apicv_active is
> true, one fewer check has to be performed. Second, static_call_cond will
> elide the function call if APICv is not present or disabled. Finally,
> in the case for AMD hardware we can remove the sync_pir_to_irr callback:
> it is only needed for apic_has_interrupt_for_ppr, and that function
> already has a fallback for !APICv.
>
> Cc: stable@vger.kernel.org
> Co-developed-by: Sean Christopherson <seanjc@google.com>
> Signed-off-by: Sean Christopherson <seanjc@google.com>
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

Reviewed-by: David Matlack <dmatlack@google.com>

> ---
> arch/x86/kvm/lapic.c | 2 +-
> arch/x86/kvm/svm/svm.c | 1 -
> arch/x86/kvm/x86.c | 18 +++++++++---------
> 3 files changed, 10 insertions(+), 11 deletions(-)
>
> diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
> index 759952dd1222..f206fc35deff 100644
> --- a/arch/x86/kvm/lapic.c
> +++ b/arch/x86/kvm/lapic.c
> @@ -707,7 +707,7 @@ static void pv_eoi_clr_pending(struct kvm_vcpu *vcpu)
> static int apic_has_interrupt_for_ppr(struct kvm_lapic *apic, u32 ppr)
> {
> int highest_irr;
> - if (apic->vcpu->arch.apicv_active)
> + if (kvm_x86_ops.sync_pir_to_irr)
> highest_irr = static_call(kvm_x86_sync_pir_to_irr)(apic->vcpu);
> else
> highest_irr = apic_find_highest_irr(apic);
> diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
> index 5630c241d5f6..d0f68d11ec70 100644
> --- a/arch/x86/kvm/svm/svm.c
> +++ b/arch/x86/kvm/svm/svm.c
> @@ -4651,7 +4651,6 @@ static struct kvm_x86_ops svm_x86_ops __initdata = {
> .load_eoi_exitmap = svm_load_eoi_exitmap,
> .hwapic_irr_update = svm_hwapic_irr_update,
> .hwapic_isr_update = svm_hwapic_isr_update,
> - .sync_pir_to_irr = kvm_lapic_find_highest_irr,
> .apicv_post_state_restore = avic_post_state_restore,
>
> .set_tss_addr = svm_set_tss_addr,
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 441f4769173e..a8f12c83db4b 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -4448,8 +4448,7 @@ void kvm_arch_vcpu_put(struct kvm_vcpu *vcpu)
> static int kvm_vcpu_ioctl_get_lapic(struct kvm_vcpu *vcpu,
> struct kvm_lapic_state *s)
> {
> - if (vcpu->arch.apicv_active)
> - static_call(kvm_x86_sync_pir_to_irr)(vcpu);
> + static_call_cond(kvm_x86_sync_pir_to_irr)(vcpu);
>
> return kvm_apic_get_state(vcpu, s);
> }
> @@ -9528,8 +9527,7 @@ static void vcpu_scan_ioapic(struct kvm_vcpu *vcpu)
> if (irqchip_split(vcpu->kvm))
> kvm_scan_ioapic_routes(vcpu, vcpu->arch.ioapic_handled_vectors);
> else {
> - if (vcpu->arch.apicv_active)
> - static_call(kvm_x86_sync_pir_to_irr)(vcpu);
> + static_call_cond(kvm_x86_sync_pir_to_irr)(vcpu);
> if (ioapic_in_kernel(vcpu->kvm))
> kvm_ioapic_scan_entry(vcpu, vcpu->arch.ioapic_handled_vectors);
> }
> @@ -9802,10 +9800,12 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
>
> /*
> * This handles the case where a posted interrupt was
> - * notified with kvm_vcpu_kick.
> + * notified with kvm_vcpu_kick. Assigned devices can
> + * use the POSTED_INTR_VECTOR even if APICv is disabled,
> + * so do it even if APICv is disabled on this vCPU.
> */
> - if (kvm_lapic_enabled(vcpu) && vcpu->arch.apicv_active)
> - static_call(kvm_x86_sync_pir_to_irr)(vcpu);
> + if (kvm_lapic_enabled(vcpu))
> + static_call_cond(kvm_x86_sync_pir_to_irr)(vcpu);
>
> if (kvm_vcpu_exit_request(vcpu)) {
> vcpu->mode = OUTSIDE_GUEST_MODE;
> @@ -9849,8 +9849,8 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
> if (likely(exit_fastpath != EXIT_FASTPATH_REENTER_GUEST))
> break;
>
> - if (kvm_lapic_enabled(vcpu) && vcpu->arch.apicv_active)
> - static_call(kvm_x86_sync_pir_to_irr)(vcpu);
> + if (kvm_lapic_enabled(vcpu))
> + static_call_cond(kvm_x86_sync_pir_to_irr)(vcpu);
>
> if (unlikely(kvm_vcpu_exit_request(vcpu))) {
> exit_fastpath = EXIT_FASTPATH_EXIT_HANDLED;
> --
> 2.27.0
>
>