linux-kernel - [PATCH v2 07/14] KVM: x86: remove unnecessary uses of PIT state lock

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Message-Id: <1455736496-374-8-git-send-email-rkrcmar@redhat.com>
Date:	Wed, 17 Feb 2016 20:14:49 +0100
From:	Radim Krčmář <rkrcmar@...hat.com>
To:	linux-kernel@...r.kernel.org
Cc:	kvm@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>,
	Yuki Shibuya <shibuya.yk@...s.nec.co.jp>
Subject: [PATCH v2 07/14] KVM: x86: remove unnecessary uses of PIT state lock

- kvm_create_pit had to lock only because it exposed kvm->arch.vpit very
  early, but initialization doesn't use kvm->arch.vpit since the last
  patch, so we can drop locking.
- kvm_free_pit is only run after there are no users of KVM and therefore
  is the sole actor.
- Locking in kvm_vm_ioctl_reinject doesn't do anything, because reinject
  is only protected at that place.
- kvm_pit_reset isn't used anywhere and its locking can be dropped if we
  hide it.

Removing useless locking allows to see what actually is being protected
by PIT state lock (values accessible from the guest).

Signed-off-by: Radim Krčmář <rkrcmar@...hat.com>
---
 v2: new

 arch/x86/kvm/i8254.c | 7 -------
 arch/x86/kvm/i8254.h | 7 ++++---
 arch/x86/kvm/x86.c   | 4 ++--
 3 files changed, 6 insertions(+), 12 deletions(-)

diff --git a/arch/x86/kvm/i8254.c b/arch/x86/kvm/i8254.c
index c11734dd5092..01f9c70ebc21 100644
--- a/arch/x86/kvm/i8254.c
+++ b/arch/x86/kvm/i8254.c
@@ -612,7 +612,6 @@ void kvm_pit_reset(struct kvm_pit *pit)
 	int i;
 	struct kvm_kpit_channel_state *c;
 
-	mutex_lock(&pit->pit_state.lock);
 	pit->pit_state.flags = 0;
 	for (i = 0; i < 3; i++) {
 		c = &pit->pit_state.channels[i];
@@ -620,7 +619,6 @@ void kvm_pit_reset(struct kvm_pit *pit)
 		c->gate = (i != 2);
 		pit_load_count(pit, i, 0);
 	}
-	mutex_unlock(&pit->pit_state.lock);
 
 	kvm_pit_reset_reinject(pit);
 }
@@ -663,7 +661,6 @@ struct kvm_pit *kvm_create_pit(struct kvm *kvm, u32 flags)
 	}
 
 	mutex_init(&pit->pit_state.lock);
-	mutex_lock(&pit->pit_state.lock);
 
 	pid = get_pid(task_tgid(current));
 	pid_nr = pid_vnr(pid);
@@ -673,7 +670,6 @@ struct kvm_pit *kvm_create_pit(struct kvm *kvm, u32 flags)
 	pit->worker_task = kthread_run(kthread_worker_fn, &pit->worker,
 				       "kvm-pit/%d", pid_nr);
 	if (IS_ERR(pit->worker_task)) {
-		mutex_unlock(&pit->pit_state.lock);
 		kvm_free_irq_source_id(kvm, pit->irq_source_id);
 		kfree(pit);
 		return NULL;
@@ -689,7 +685,6 @@ struct kvm_pit *kvm_create_pit(struct kvm *kvm, u32 flags)
 	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);
 
@@ -737,13 +732,11 @@ void kvm_free_pit(struct kvm *kvm)
 					       &kvm->arch.vpit->mask_notifier);
 		kvm_unregister_irq_ack_notifier(kvm,
 				&kvm->arch.vpit->pit_state.irq_ack_notifier);
-		mutex_lock(&kvm->arch.vpit->pit_state.lock);
 		timer = &kvm->arch.vpit->pit_state.timer;
 		hrtimer_cancel(timer);
 		flush_kthread_work(&kvm->arch.vpit->expired);
 		kthread_stop(kvm->arch.vpit->worker_task);
 		kvm_free_irq_source_id(kvm, kvm->arch.vpit->irq_source_id);
-		mutex_unlock(&kvm->arch.vpit->pit_state.lock);
 		kfree(kvm->arch.vpit);
 	}
 }
diff --git a/arch/x86/kvm/i8254.h b/arch/x86/kvm/i8254.h
index a6aceaf08df5..568d87ec3698 100644
--- a/arch/x86/kvm/i8254.h
+++ b/arch/x86/kvm/i8254.h
@@ -22,17 +22,19 @@ struct kvm_kpit_channel_state {
 };
 
 struct kvm_kpit_state {
+	/* All members before "struct mutex lock" are protected by the lock. */
 	struct kvm_kpit_channel_state channels[3];
 	u32 flags;
 	bool is_periodic;
 	s64 period; 				/* unit: ns */
 	struct hrtimer timer;
-	atomic_t pending;			/* accumulated triggered timers */
 	bool reinject;
-	struct kvm *kvm;
 	u32    speaker_data_on;
+
 	struct mutex lock;
+	struct kvm *kvm;
 	struct kvm_pit *pit;
+	atomic_t pending; /* accumulated triggered timers */
 	atomic_t irq_ack;
 	struct kvm_irq_ack_notifier irq_ack_notifier;
 };
@@ -59,7 +61,6 @@ struct kvm_pit {
 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_load_count(struct kvm_pit *pit, int channel, u32 val,
 		int hpet_legacy_start);
 
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 57b296466bf0..f2f7ba74da6b 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -3685,9 +3685,9 @@ 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);
+
 	return 0;
 }
 
-- 
2.7.1