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@xxxxxxxxxx>
Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Signed-off-by: Maxim Levitsky <mlevitsk@xxxxxxxxxx>
---
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);
--
2.26.3
