KVM: SVM: fix race between interrupt delivery and AVIC inhibition

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.

Incomplete IPI vmexit has the same races as svm_deliver_avic_intr, and
in fact it can be handled in exactly the same way; the only difference
lies in who has set IRR, whether svm_deliver_interrupt or the processor.
Therefore, svm_complete_interrupt_delivery can be used to fix incomplete
IPI vmexits 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>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 8 insertions, 40 deletions

diff --git a/arch/x86/kvm/svm/avic.c b/arch/x86/kvm/svm/avic.c
index 2b2932f04411..fb3e20791338 100644
--- a/arch/x86/kvm/svm/avic.c
+++ b/arch/x86/kvm/svm/avic.c
@@ -269,7 +269,7 @@ static int avic_init_backing_page(struct kvm_vcpu *vcpu)
 	return 0;
 }
 
-static void avic_ring_doorbell(struct kvm_vcpu *vcpu)
+void avic_ring_doorbell(struct kvm_vcpu *vcpu)
 {
 	/*
 	 * Note, the vCPU could get migrated to a different pCPU at any point,
@@ -300,8 +300,13 @@ 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);
+		}
 	}
 }
 
@@ -663,43 +668,6 @@ void svm_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;
-
-	/*
-	 * 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) {
-		/*
-		 * Signal the doorbell to tell hardware to inject the IRQ.  If
-		 * the vCPU exits the guest before the doorbell chimes, hardware
-		 * will automatically process AVIC interrupts at the next 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);
-	}
-
-	return 0;
-}
-
 bool svm_dy_apicv_has_pending_interrupt(struct kvm_vcpu *vcpu)
 {
 	return false;