If svm_deliver_avic_intr is called just after the target vcpu's AVIC got inhibited, it might read a stale value of vcpu->arch.apicv_active which can lead to the target vCPU not noticing the interrupt.
To fix this use load-acquire/store-release so that, if the target vCPU is IN_GUEST_MODE, we're guaranteed to see a previous disabling of the AVIC. If AVIC has been disabled in the meanwhile, proceed with the KVM_REQ_EVENT-based delivery.
All this complicated logic is actually exactly how we can handle an incomplete IPI vmexit; the only difference lies in who sets IRR, whether KVM or the processor.
Also incomplete IPI vmexit also has the same races as svm_deliver_avic_intr. Therefore use the avic_kick_target_vcpu there as well.
Co-developed-by: Paolo Bonzini pbonzini@redhat.com Signed-off-by: Paolo Bonzini pbonzini@redhat.com Signed-off-by: Maxim Levitsky mlevitsk@redhat.com --- arch/x86/kvm/svm/avic.c | 73 ++++++++++++++--------------------------- arch/x86/kvm/svm/svm.c | 65 ++++++++++++++++++++++++++++-------- arch/x86/kvm/svm/svm.h | 3 ++ arch/x86/kvm/x86.c | 4 ++- 4 files changed, 82 insertions(+), 63 deletions(-)
diff --git a/arch/x86/kvm/svm/avic.c b/arch/x86/kvm/svm/avic.c index fabfc337e1c35..4c2d622b3b9f0 100644 --- a/arch/x86/kvm/svm/avic.c +++ b/arch/x86/kvm/svm/avic.c @@ -269,6 +269,24 @@ static int avic_init_backing_page(struct kvm_vcpu *vcpu) return 0; }
+ +void avic_ring_doorbell(struct kvm_vcpu *vcpu) +{ + /* + * Note, the vCPU could get migrated to a different pCPU at any + * point, which could result in signalling the wrong/previous + * pCPU. But if that happens the vCPU is guaranteed to do a + * VMRUN (after being migrated) and thus will process pending + * interrupts, i.e. a doorbell is not needed (and the spurious + * one is harmless). + */ + int cpu = READ_ONCE(vcpu->cpu); + + if (cpu != get_cpu()) + wrmsrl(MSR_AMD64_SVM_AVIC_DOORBELL, kvm_cpu_get_apicid(cpu)); + put_cpu(); +} + static void avic_kick_target_vcpus(struct kvm *kvm, struct kvm_lapic *source, u32 icrl, u32 icrh) { @@ -284,8 +302,13 @@ static void avic_kick_target_vcpus(struct kvm *kvm, struct kvm_lapic *source, kvm_for_each_vcpu(i, vcpu, kvm) { if (kvm_apic_match_dest(vcpu, source, icrl & APIC_SHORT_MASK, GET_APIC_DEST_FIELD(icrh), - icrl & APIC_DEST_MASK)) - kvm_vcpu_wake_up(vcpu); + icrl & APIC_DEST_MASK)) { + vcpu->arch.apic->irr_pending = true; + svm_complete_interrupt_delivery(vcpu, + icrl & APIC_MODE_MASK, + icrl & APIC_INT_LEVELTRIG, + icrl & APIC_VECTOR_MASK); + } } }
@@ -649,52 +672,6 @@ void avic_load_eoi_exitmap(struct kvm_vcpu *vcpu, u64 *eoi_exit_bitmap) return; }
-int svm_deliver_avic_intr(struct kvm_vcpu *vcpu, int vec) -{ - if (!vcpu->arch.apicv_active) - return -1; - - kvm_lapic_set_irr(vec, vcpu->arch.apic); - - /* - * Pairs with the smp_mb_*() after setting vcpu->guest_mode in - * vcpu_enter_guest() to ensure the write to the vIRR is ordered before - * the read of guest_mode, which guarantees that either VMRUN will see - * and process the new vIRR entry, or that the below code will signal - * the doorbell if the vCPU is already running in the guest. - */ - smp_mb__after_atomic(); - - /* - * Signal the doorbell to tell hardware to inject the IRQ if the vCPU - * is in the guest. If the vCPU is not in the guest, hardware will - * automatically process AVIC interrupts at VMRUN. - */ - if (vcpu->mode == IN_GUEST_MODE) { - int cpu = READ_ONCE(vcpu->cpu); - - /* - * Note, the vCPU could get migrated to a different pCPU at any - * point, which could result in signalling the wrong/previous - * pCPU. But if that happens the vCPU is guaranteed to do a - * VMRUN (after being migrated) and thus will process pending - * interrupts, i.e. a doorbell is not needed (and the spurious - * one is harmless). - */ - if (cpu != get_cpu()) - wrmsrl(MSR_AMD64_SVM_AVIC_DOORBELL, kvm_cpu_get_apicid(cpu)); - put_cpu(); - } else { - /* - * Wake the vCPU if it was blocking. KVM will then detect the - * pending IRQ when checking if the vCPU has a wake event. - */ - kvm_vcpu_wake_up(vcpu); - } - - return 0; -} - bool avic_dy_apicv_has_pending_interrupt(struct kvm_vcpu *vcpu) { return false; diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c index 22e614008cf59..18d4d87e12e15 100644 --- a/arch/x86/kvm/svm/svm.c +++ b/arch/x86/kvm/svm/svm.c @@ -3310,20 +3310,6 @@ static void svm_inject_irq(struct kvm_vcpu *vcpu) SVM_EVTINJ_VALID | SVM_EVTINJ_TYPE_INTR; }
-static void svm_deliver_interrupt(struct kvm_lapic *apic, int delivery_mode, - int trig_mode, int vector) -{ - struct kvm_vcpu *vcpu = apic->vcpu; - - if (svm_deliver_avic_intr(vcpu, vector)) { - kvm_lapic_set_irr(vector, apic); - kvm_make_request(KVM_REQ_EVENT, vcpu); - kvm_vcpu_kick(vcpu); - } else { - trace_kvm_apicv_accept_irq(vcpu->vcpu_id, delivery_mode, - trig_mode, vector); - } -}
static void svm_update_cr8_intercept(struct kvm_vcpu *vcpu, int tpr, int irr) { @@ -4142,6 +4128,57 @@ static int svm_check_intercept(struct kvm_vcpu *vcpu, return ret; }
+void svm_complete_interrupt_delivery(struct kvm_vcpu *vcpu, int delivery_mode, + int trig_mode, int vec) +{ + /* + * vcpu->arch.apicv_active must be read after vcpu->mode. + * Pairs with smp_store_release in vcpu_enter_guest. + */ + bool in_guest_mode = (smp_load_acquire(&vcpu->mode) == IN_GUEST_MODE); + + if (!READ_ONCE(vcpu->arch.apicv_active)) { + /* + * Manually signal the event + */ + kvm_make_request(KVM_REQ_EVENT, vcpu); + kvm_vcpu_kick(vcpu); + return; + } + + trace_kvm_apicv_accept_irq(vcpu->vcpu_id, delivery_mode, trig_mode, vec); + + if (in_guest_mode) + /* + * Signal the doorbell to tell hardware to inject the IRQ if the vCPU + * is in the guest. If the vCPU is not in the guest, hardware will + * automatically process AVIC interrupts at VMRUN. + */ + avic_ring_doorbell(vcpu); + else + /* + * Wake the vCPU if it was blocking. KVM will then detect the + * pending IRQ when checking if the vCPU has a wake event. + */ + kvm_vcpu_wake_up(vcpu); +} + +static void svm_deliver_interrupt(struct kvm_lapic *apic, int delivery_mode, + int trig_mode, int vec) +{ + kvm_lapic_set_irr(vec, apic); + + /* + * Pairs with the smp_mb_*() after setting vcpu->guest_mode in + * vcpu_enter_guest() to ensure the write to the vIRR is ordered before + * the read of guest_mode, which guarantees that either VMRUN will see + * and process the new vIRR entry, or that the below code will signal + * the doorbell if the vCPU is already running in the guest. + */ + smp_mb__after_atomic(); + svm_complete_interrupt_delivery(apic->vcpu, delivery_mode, trig_mode, vec); +} + static void svm_handle_exit_irqoff(struct kvm_vcpu *vcpu) { } diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h index 6343558982c73..83f9f95eced3e 100644 --- a/arch/x86/kvm/svm/svm.h +++ b/arch/x86/kvm/svm/svm.h @@ -488,6 +488,8 @@ void svm_set_gif(struct vcpu_svm *svm, bool value); int svm_invoke_exit_handler(struct kvm_vcpu *vcpu, u64 exit_code); void set_msr_interception(struct kvm_vcpu *vcpu, u32 *msrpm, u32 msr, int read, int write); +void svm_complete_interrupt_delivery(struct kvm_vcpu *vcpu, int delivery_mode, + int trig_mode, int vec);
/* nested.c */
@@ -577,6 +579,7 @@ int avic_pi_update_irte(struct kvm *kvm, unsigned int host_irq, uint32_t guest_irq, bool set); void avic_vcpu_blocking(struct kvm_vcpu *vcpu); void avic_vcpu_unblocking(struct kvm_vcpu *vcpu); +void avic_ring_doorbell(struct kvm_vcpu *vcpu);
/* sev.c */
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 6f69f3e3635e2..8cb5390f75efe 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -10039,7 +10039,9 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu) * result in virtual interrupt delivery. */ local_irq_disable(); - vcpu->mode = IN_GUEST_MODE; + + /* Store vcpu->apicv_active before vcpu->mode. */ + smp_store_release(&vcpu->mode, IN_GUEST_MODE);
srcu_read_unlock(&vcpu->kvm->srcu, vcpu->srcu_idx);