Replace the full "kick" with just the "wake" in the fallback path when triggering a virtual interrupt via a posted interrupt fails because the guest is not IN_GUEST_MODE. If the guest transitions into guest mode between the check and the kick, then it's guaranteed to see the pending interrupt as KVM syncs the PIR to IRR (and onto GUEST_RVI) after setting IN_GUEST_MODE. Kicking the guest in this case is nothing more than an unnecessary VM-Exit (and host IRQ). Opportunistically update comments to explain the various ordering rules and barriers at play. Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx> --- arch/x86/kvm/vmx/vmx.c | 16 ++++++++++++++-- arch/x86/kvm/x86.c | 5 +++-- 2 files changed, 17 insertions(+), 4 deletions(-) diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c index 13e732a818f3..44d760dde0f9 100644 --- a/arch/x86/kvm/vmx/vmx.c +++ b/arch/x86/kvm/vmx/vmx.c @@ -3978,10 +3978,16 @@ static int vmx_deliver_nested_posted_interrupt(struct kvm_vcpu *vcpu, * we will accomplish it in the next vmentry. */ vmx->nested.pi_pending = true; + /* + * The smp_wmb() in kvm_make_request() pairs with the smp_mb_*() + * after setting vcpu->mode in vcpu_enter_guest(), thus the vCPU + * is guaranteed to see the event request if triggering a posted + * interrupt "fails" because vcpu->mode != IN_GUEST_MODE. + */ kvm_make_request(KVM_REQ_EVENT, vcpu); /* the PIR and ON have been set by L1. */ if (!kvm_vcpu_trigger_posted_interrupt(vcpu, true)) - kvm_vcpu_kick(vcpu); + kvm_vcpu_wake_up(vcpu); return 0; } return -1; @@ -4012,9 +4018,15 @@ static int vmx_deliver_posted_interrupt(struct kvm_vcpu *vcpu, int vector) if (pi_test_and_set_on(&vmx->pi_desc)) return 0; + /* + * The implied barrier in pi_test_and_set_on() pairs with the smp_mb_*() + * after setting vcpu->mode in vcpu_enter_guest(), thus the vCPU is + * guaranteed to see PID.ON=1 and sync the PIR to IRR if triggering a + * posted interrupt "fails" because vcpu->mode != IN_GUEST_MODE. + */ if (vcpu != kvm_get_running_vcpu() && !kvm_vcpu_trigger_posted_interrupt(vcpu, false)) - kvm_vcpu_kick(vcpu); + kvm_vcpu_wake_up(vcpu); return 0; } diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 9643f23c28c7..274d295cabfb 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -9752,8 +9752,9 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu) smp_mb__after_srcu_read_unlock(); /* - * This handles the case where a posted interrupt was - * notified with kvm_vcpu_kick. + * Process pending posted interrupts to handle the case where the + * notification IRQ arrived in the host, or was never sent (because the + * target vCPU wasn't running). */ if (kvm_lapic_enabled(vcpu) && vcpu->arch.apicv_active) static_call(kvm_x86_sync_pir_to_irr)(vcpu); -- 2.33.0.882.g93a45727a2-goog
