KVM: i8254: remove notifiers from PIT discard policy

Discard policy doesn't rely on information from notifiers, so we don't
need to register notifiers unconditionally.  We kept correct counts in
case userspace switched between policies during runtime, but that can be
avoided by reseting the state.

Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 27 insertions, 11 deletions

diff --git a/arch/x86/kvm/i8254.c b/arch/x86/kvm/i8254.c
index b8582fbe4fcf..7a2f14bdf4b5 100644
--- a/arch/x86/kvm/i8254.c
+++ b/arch/x86/kvm/i8254.c
@@ -225,7 +225,7 @@ static void kvm_pit_ack_irq(struct kvm_irq_ack_notifier *kian)
 	 * inc(pending) in pit_timer_fn and xchg(irq_ack, 0) in pit_do_work.
 	 */
 	smp_mb();
-	if (atomic_dec_if_positive(&ps->pending) > 0 && ps->reinject)
+	if (atomic_dec_if_positive(&ps->pending) > 0)
 		queue_kthread_work(&ps->pit->worker, &ps->pit->expired);
 }
 
@@ -301,6 +301,27 @@ static inline void kvm_pit_reset_reinject(struct kvm_pit *pit)
 	atomic_set(&pit->pit_state.irq_ack, 1);
 }
 
+void kvm_pit_set_reinject(struct kvm_pit *pit, bool reinject)
+{
+	struct kvm_kpit_state *ps = &pit->pit_state;
+	struct kvm *kvm = pit->kvm;
+
+	if (ps->reinject == reinject)
+		return;
+
+	if (reinject) {
+		/* The initial state is preserved while ps->reinject == 0. */
+		kvm_pit_reset_reinject(pit);
+		kvm_register_irq_ack_notifier(kvm, &ps->irq_ack_notifier);
+		kvm_register_irq_mask_notifier(kvm, 0, &pit->mask_notifier);
+	} else {
+		kvm_unregister_irq_ack_notifier(kvm, &ps->irq_ack_notifier);
+		kvm_unregister_irq_mask_notifier(kvm, 0, &pit->mask_notifier);
+	}
+
+	ps->reinject = reinject;
+}
+
 static void create_pit_timer(struct kvm_pit *pit, u32 val, int is_period)
 {
 	struct kvm_kpit_state *ps = &pit->pit_state;
@@ -681,15 +702,14 @@ struct kvm_pit *kvm_create_pit(struct kvm *kvm, u32 flags)
 	pit_state = &pit->pit_state;
 	pit_state->pit = pit;
 	hrtimer_init(&pit_state->timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
+
 	pit_state->irq_ack_notifier.gsi = 0;
 	pit_state->irq_ack_notifier.irq_acked = kvm_pit_ack_irq;
-	kvm_register_irq_ack_notifier(kvm, &pit_state->irq_ack_notifier);
-	pit_state->reinject = true;
+	pit->mask_notifier.func = pit_mask_notifer;
 
 	kvm_pit_reset(pit);
 
-	pit->mask_notifier.func = pit_mask_notifer;
-	kvm_register_irq_mask_notifier(kvm, 0, &pit->mask_notifier);
+	kvm_pit_set_reinject(pit, true);
 
 	kvm_iodevice_init(&pit->dev, &pit_dev_ops);
 	ret = kvm_io_bus_register_dev(kvm, KVM_PIO_BUS, KVM_PIT_BASE_ADDRESS,
@@ -712,8 +732,7 @@ fail_unregister:
 	kvm_io_bus_unregister_dev(kvm, KVM_PIO_BUS, &pit->dev);
 
 fail:
-	kvm_unregister_irq_mask_notifier(kvm, 0, &pit->mask_notifier);
-	kvm_unregister_irq_ack_notifier(kvm, &pit_state->irq_ack_notifier);
+	kvm_pit_set_reinject(pit, false);
 	kvm_free_irq_source_id(kvm, pit->irq_source_id);
 	kthread_stop(pit->worker_task);
 	kfree(pit);
@@ -728,10 +747,7 @@ void kvm_free_pit(struct kvm *kvm)
 		kvm_io_bus_unregister_dev(kvm, KVM_PIO_BUS, &kvm->arch.vpit->dev);
 		kvm_io_bus_unregister_dev(kvm, KVM_PIO_BUS,
 					      &kvm->arch.vpit->speaker_dev);
-		kvm_unregister_irq_mask_notifier(kvm, 0,
-					       &kvm->arch.vpit->mask_notifier);
-		kvm_unregister_irq_ack_notifier(kvm,
-				&kvm->arch.vpit->pit_state.irq_ack_notifier);
+		kvm_pit_set_reinject(kvm->arch.vpit, false);
 		timer = &kvm->arch.vpit->pit_state.timer;
 		hrtimer_cancel(timer);
 		flush_kthread_work(&kvm->arch.vpit->expired);