KVM: Reset PIT irq injection logic when the PIT IRQ is unmasked

While the PIT is masked the guest cannot ack the irq, so the reinject logic
will never allow the interrupt to be injected.

Fix by resetting the reinjection counters on unmask.

Unbreaks Xen.
Signed-off-by: Avi Kivity <avi@redhat.com>

arch/x86/kvm/i8254.c

@@ -539,6 +539,16 @@ void kvm_pit_reset(struct kvm_pit *pit)
 	pit->pit_state.irq_ack = 1;
 }
 
+static void pit_mask_notifer(struct kvm_irq_mask_notifier *kimn, bool mask)
+{
+	struct kvm_pit *pit = container_of(kimn, struct kvm_pit, mask_notifier);
+
+	if (!mask) {
+		atomic_set(&pit->pit_state.pit_timer.pending, 0);
+		pit->pit_state.irq_ack = 1;
+	}
+}
+
 struct kvm_pit *kvm_create_pit(struct kvm *kvm)
 {
 	struct kvm_pit *pit;
@@ -586,6 +596,9 @@ struct kvm_pit *kvm_create_pit(struct kvm *kvm)
 
 	kvm_pit_reset(pit);
 
+	pit->mask_notifier.func = pit_mask_notifer;
+	kvm_register_irq_mask_notifier(kvm, 0, &pit->mask_notifier);
+
 	return pit;
 }
 
@@ -594,6 +607,8 @@ void kvm_free_pit(struct kvm *kvm)
 	struct hrtimer *timer;
 
 	if (kvm->arch.vpit) {
+		kvm_unregister_irq_mask_notifier(kvm, 0,
+					       &kvm->arch.vpit->mask_notifier);
 		mutex_lock(&kvm->arch.vpit->pit_state.lock);
 		timer = &kvm->arch.vpit->pit_state.pit_timer.timer;
 		hrtimer_cancel(timer);

arch/x86/kvm/i8254.h

@@ -46,6 +46,7 @@ struct kvm_pit {
 	struct kvm *kvm;
 	struct kvm_kpit_state pit_state;
 	int irq_source_id;
+	struct kvm_irq_mask_notifier mask_notifier;
 };
 
 #define KVM_PIT_BASE_ADDRESS	    0x40