[PATCH 4/4] KVM: x86: remove notifiers from PIT discard policy

["Radim Krčmář" <rkrcmar@redhat.com>]

Discard policy doesn't rely on information from notifiers, so we don't
need to register notifiers unconditionally.

Use of ps->lock doesn't make sense, but isn't any worse than before.

Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
---
 arch/x86/kvm/i8254.c | 44 ++++++++++++++++++++++++++++++--------------
 arch/x86/kvm/i8254.h |  1 +
 arch/x86/kvm/x86.c   |  6 +++---
 3 files changed, 34 insertions(+), 17 deletions(-)

diff --git a/arch/x86/kvm/i8254.c b/arch/x86/kvm/i8254.c
index fc554fbf71a7..f1dfc250bbe0 100644
--- a/arch/x86/kvm/i8254.c
+++ b/arch/x86/kvm/i8254.c
@@ -237,9 +237,6 @@ static void kvm_pit_ack_irq(struct kvm_irq_ack_notifier *kian)
 	struct kvm_kpit_state *ps = container_of(kian, struct kvm_kpit_state,
 						 irq_ack_notifier);
 
-	if (!ps->reinject)
-		return;
-
 	atomic_set(&ps->irq_ack, 1);
 	if (atomic_add_unless(&ps->pending, -1, 0))
 		/* in this case, we had multiple outstanding pit interrupts
@@ -708,14 +705,13 @@ struct kvm_pit *kvm_create_pit(struct kvm *kvm, u32 flags)
 	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;
 	mutex_unlock(&pit->pit_state.lock);
 
-	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_pit_reset(pit);
 
 	kvm_iodevice_init(&pit->dev, &pit_dev_ops);
 	ret = kvm_io_bus_register_dev(kvm, KVM_PIO_BUS, KVM_PIT_BASE_ADDRESS,
@@ -738,14 +734,37 @@ 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);
 	return NULL;
 }
 
+void kvm_pit_set_reinject(struct kvm_pit *pit, bool reinject)
+{
+	/* Implicit BUG on NULL dereference. */
+	struct kvm_kpit_state *ps = &pit->pit_state;
+	struct kvm *kvm = pit->kvm;
+
+	mutex_lock(&ps->lock);
+
+	if (ps->reinject == reinject)
+		goto out;
+
+	ps->reinject = reinject;
+	if (reinject) {
+		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);
+	}
+out:
+	mutex_unlock(&ps->lock);
+}
+
 void kvm_free_pit(struct kvm *kvm)
 {
 	struct hrtimer *timer;
@@ -754,10 +773,7 @@ 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);
 		mutex_lock(&kvm->arch.vpit->pit_state.lock);
 		timer = &kvm->arch.vpit->pit_state.timer;
 		hrtimer_cancel(timer);
diff --git a/arch/x86/kvm/i8254.h b/arch/x86/kvm/i8254.h
index f8cf4b84f435..7ac94bc0799f 100644
--- a/arch/x86/kvm/i8254.h
+++ b/arch/x86/kvm/i8254.h
@@ -60,5 +60,6 @@ void kvm_pit_load_count(struct kvm *kvm, int channel, u32 val, int hpet_legacy_s
 struct kvm_pit *kvm_create_pit(struct kvm *kvm, u32 flags);
 void kvm_free_pit(struct kvm *kvm);
 void kvm_pit_reset(struct kvm_pit *pit);
+void kvm_pit_set_reinject(struct kvm_pit *pit, bool reinject);
 
 #endif
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 5b937fdebc66..6bc03141e809 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -3652,9 +3652,9 @@ static int kvm_vm_ioctl_reinject(struct kvm *kvm,
 {
 	if (!kvm->arch.vpit)
 		return -ENXIO;
-	mutex_lock(&kvm->arch.vpit->pit_state.lock);
-	kvm->arch.vpit->pit_state.reinject = control->pit_reinject;
-	mutex_unlock(&kvm->arch.vpit->pit_state.lock);
+
+	kvm_pit_set_reinject(kvm->arch.vpit, control->pit_reinject);
+
 	return 0;
 }
 
-- 
2.7.0