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[PATCH v2 08/14] KVM: x86: remove notifiers from PIT discard policy

From Radim Krčmář <rkrcmar@redhat.com>
Newsgroups linux.kernel
Subject [PATCH v2 08/14] KVM: x86: remove notifiers from PIT discard policy
Date 2016-02-17 20:20 +0100
Message-ID <r3fNN-2nq-39@gated-at.bofh.it> (permalink)
References <r3fNM-2nq-7@gated-at.bofh.it>
Organization linux.* mail to news gateway

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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>
---
 v2:
 * lock the ioctl
 * rebase

 arch/x86/kvm/i8254.c | 38 +++++++++++++++++++++++++++-----------
 arch/x86/kvm/i8254.h |  1 +
 arch/x86/kvm/x86.c   | 12 ++++++++++--
 3 files changed, 38 insertions(+), 13 deletions(-)

diff --git a/arch/x86/kvm/i8254.c b/arch/x86/kvm/i8254.c
index 01f9c70ebc21..e514f7fa0093 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);
diff --git a/arch/x86/kvm/i8254.h b/arch/x86/kvm/i8254.h
index 568d87ec3698..47a96e803aab 100644
--- a/arch/x86/kvm/i8254.h
+++ b/arch/x86/kvm/i8254.h
@@ -63,5 +63,6 @@ void kvm_free_pit(struct kvm *kvm);
 
 void kvm_pit_load_count(struct kvm_pit *pit, int channel, u32 val,
 		int hpet_legacy_start);
+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 f2f7ba74da6b..785cc781673d 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -3683,10 +3683,18 @@ static int kvm_vm_ioctl_set_pit2(struct kvm *kvm, struct kvm_pit_state2 *ps)
 static int kvm_vm_ioctl_reinject(struct kvm *kvm,
 				 struct kvm_reinject_control *control)
 {
-	if (!kvm->arch.vpit)
+	struct kvm_pit *pit = kvm->arch.vpit;
+
+	if (!pit)
 		return -ENXIO;
 
-	kvm->arch.vpit->pit_state.reinject = control->pit_reinject;
+	/* pit->pit_state.lock was overloaded to prevent userspace from getting
+	 * an inconsistent state after running multiple KVM_REINJECT_CONTROL
+	 * ioctls in parallel.  Use a separate lock if that ioctl isn't rare.
+	 */
+	mutex_lock(&pit->pit_state.lock);
+	kvm_pit_set_reinject(pit, control->pit_reinject);
+	mutex_unlock(&pit->pit_state.lock);
 
 	return 0;
 }
-- 
2.7.1

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[PATCH v2 00/14] KVM: x86: change PIT discard policy and untangle related code Radim Krčmář <rkrcmar@redhat.com> - 2016-02-17 20:20 +0100
  [PATCH v2 02/14] KVM: x86: simplify atomics in kvm_pit_ack_irq Radim Krčmář <rkrcmar@redhat.com> - 2016-02-17 20:20 +0100
    Re: [PATCH v2 02/14] KVM: x86: simplify atomics in kvm_pit_ack_irq Paolo Bonzini <pbonzini@redhat.com> - 2016-02-18 19:10 +0100
      Re: [PATCH v2 02/14] KVM: x86: simplify atomics in kvm_pit_ack_irq Paolo Bonzini <pbonzini@redhat.com> - 2016-02-19 17:00 +0100
      Re: [PATCH v2 02/14] KVM: x86: simplify atomics in kvm_pit_ack_irq Radim Krčmář <rkrcmar@redhat.com> - 2016-02-19 17:00 +0100
  [PATCH v2 14/14] KVM: x86: move PIT timer function initialization Radim Krčmář <rkrcmar@redhat.com> - 2016-02-17 20:20 +0100
  [PATCH v2 05/14] KVM: x86: tone down WARN_ON pit.state_lock Radim Krčmář <rkrcmar@redhat.com> - 2016-02-17 20:20 +0100
  [PATCH v2 06/14] KVM: x86: pass struct kvm_pit instead of kvm in PIT Radim Krčmář <rkrcmar@redhat.com> - 2016-02-17 20:20 +0100
  [PATCH v2 09/14] KVM: x86: refactor kvm_create_pit Radim Krčmář <rkrcmar@redhat.com> - 2016-02-17 20:20 +0100
  [PATCH v2 04/14] KVM: x86: use atomic_t instead of pit.inject_lock Radim Krčmář <rkrcmar@redhat.com> - 2016-02-17 20:20 +0100
  [PATCH v2 13/14] KVM: x86: don't assume layout of kvm_kpit_state Radim Krčmář <rkrcmar@redhat.com> - 2016-02-17 20:20 +0100
  [PATCH v2 01/14] KVM: x86: change PIT discard tick policy Radim Krčmář <rkrcmar@redhat.com> - 2016-02-17 20:20 +0100
    Re: [PATCH v2 01/14] KVM: x86: change PIT discard tick policy Paolo Bonzini <pbonzini@redhat.com> - 2016-02-18 17:20 +0100
      Re: [PATCH v2 01/14] KVM: x86: change PIT discard tick policy Radim Krčmář <rkrcmar@redhat.com> - 2016-02-18 18:00 +0100
        Re: [PATCH v2 01/14] KVM: x86: change PIT discard tick policy Paolo Bonzini <pbonzini@redhat.com> - 2016-02-18 18:40 +0100
          Re: [PATCH v2 01/14] KVM: x86: change PIT discard tick policy Paolo Bonzini <pbonzini@redhat.com> - 2016-02-18 19:00 +0100
            Re: [PATCH v2 01/14] KVM: x86: change PIT discard tick policy Radim Krčmář <rkrcmar@redhat.com> - 2016-02-19 15:50 +0100
    Re: [PATCH v2 01/14] KVM: x86: change PIT discard tick policy Paolo Bonzini <pbonzini@redhat.com> - 2016-02-18 19:50 +0100
  [PATCH v2 08/14] KVM: x86: remove notifiers from PIT discard policy Radim Krčmář <rkrcmar@redhat.com> - 2016-02-17 20:20 +0100
    Re: [PATCH v2 08/14] KVM: x86: remove notifiers from PIT discard  policy Paolo Bonzini <pbonzini@redhat.com> - 2016-02-18 19:10 +0100
    Re: [PATCH v2 08/14] KVM: x86: remove notifiers from PIT discard  policy Paolo Bonzini <pbonzini@redhat.com> - 2016-02-18 19:10 +0100
      Re: [PATCH v2 08/14] KVM: x86: remove notifiers from PIT discard  policy Radim Krčmář <rkrcmar@redhat.com> - 2016-02-19 16:10 +0100
        Re: [PATCH v2 08/14] KVM: x86: remove notifiers from PIT discard  policy Paolo Bonzini <pbonzini@redhat.com> - 2016-02-19 16:10 +0100
          Re: [PATCH v2 08/14] KVM: x86: remove notifiers from PIT discard  policy Radim Krčmář <rkrcmar@redhat.com> - 2016-02-19 16:10 +0100
  [PATCH v2 10/14] KVM: x86: refactor kvm_free_pit Radim Krčmář <rkrcmar@redhat.com> - 2016-02-17 20:20 +0100
  [PATCH v2 11/14] KVM: x86: remove pit and kvm from kvm_kpit_state Radim Krčmář <rkrcmar@redhat.com> - 2016-02-17 20:20 +0100
  [PATCH v2 07/14] KVM: x86: remove unnecessary uses of PIT state lock Radim Krčmář <rkrcmar@redhat.com> - 2016-02-17 20:20 +0100
    Re: [PATCH v2 07/14] KVM: x86: remove unnecessary uses of PIT state  lock Paolo Bonzini <pbonzini@redhat.com> - 2016-02-18 19:10 +0100
      Re: [PATCH v2 07/14] KVM: x86: remove unnecessary uses of PIT state  lock Radim Krčmář <rkrcmar@redhat.com> - 2016-02-19 15:50 +0100
  [PATCH v2 03/14] KVM: x86: add kvm_pit_reset_reinject Radim Krčmář <rkrcmar@redhat.com> - 2016-02-17 20:30 +0100
  Re: [PATCH v2 00/14] KVM: x86: change PIT discard policy and untangle  related code Paolo Bonzini <pbonzini@redhat.com> - 2016-02-18 19:20 +0100

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