[PATCH] KVM: Convert intx_mask_lock to spin lock

[PATCH] KVM: Convert intx_mask_lock to spin lock

[Jan Kiszka]

As kvm_notify_acked_irq calls kvm_assigned_dev_ack_irq under
rcu_read_lock, we cannot use a mutex in the latter function. Switch to a
spin lock to address this.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
---
 include/linux/kvm_host.h |    2 +-
 virt/kvm/assigned-dev.c  |   14 +++++++-------
 2 files changed, 8 insertions(+), 8 deletions(-)

diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index b18ae78..6cf158c 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -568,7 +568,7 @@ struct kvm_assigned_dev_kernel {
 	struct pci_dev *dev;
 	struct kvm *kvm;
 	spinlock_t intx_lock;
-	struct mutex intx_mask_lock;
+	spinlock_t intx_mask_lock;
 	char irq_name[32];
 	struct pci_saved_state *pci_saved_state;
 };
diff --git a/virt/kvm/assigned-dev.c b/virt/kvm/assigned-dev.c
index 08e0571..01f572c 100644
--- a/virt/kvm/assigned-dev.c
+++ b/virt/kvm/assigned-dev.c
@@ -77,11 +77,11 @@ kvm_assigned_dev_raise_guest_irq(struct kvm_assigned_dev_kernel *assigned_dev,
 {
 	if (unlikely(assigned_dev->irq_requested_type &
 		     KVM_DEV_IRQ_GUEST_INTX)) {
-		mutex_lock(&assigned_dev->intx_mask_lock);
+		spin_lock(&assigned_dev->intx_mask_lock);
 		if (!(assigned_dev->flags & KVM_DEV_ASSIGN_MASK_INTX))
 			kvm_set_irq(assigned_dev->kvm,
 				    assigned_dev->irq_source_id, vector, 1);
-		mutex_unlock(&assigned_dev->intx_mask_lock);
+		spin_unlock(&assigned_dev->intx_mask_lock);
 	} else
 		kvm_set_irq(assigned_dev->kvm, assigned_dev->irq_source_id,
 			    vector, 1);
@@ -141,7 +141,7 @@ static void kvm_assigned_dev_ack_irq(struct kvm_irq_ack_notifier *kian)
 
 	kvm_set_irq(dev->kvm, dev->irq_source_id, dev->guest_irq, 0);
 
-	mutex_lock(&dev->intx_mask_lock);
+	spin_lock(&dev->intx_mask_lock);
 
 	if (!(dev->flags & KVM_DEV_ASSIGN_MASK_INTX)) {
 		bool reassert = false;
@@ -165,7 +165,7 @@ static void kvm_assigned_dev_ack_irq(struct kvm_irq_ack_notifier *kian)
 				    dev->guest_irq, 1);
 	}
 
-	mutex_unlock(&dev->intx_mask_lock);
+	spin_unlock(&dev->intx_mask_lock);
 }
 
 static void deassign_guest_irq(struct kvm *kvm,
@@ -707,7 +707,7 @@ static int kvm_vm_ioctl_assign_device(struct kvm *kvm,
 	match->flags = assigned_dev->flags;
 	match->dev = dev;
 	spin_lock_init(&match->intx_lock);
-	mutex_init(&match->intx_mask_lock);
+	spin_lock_init(&match->intx_mask_lock);
 	match->irq_source_id = -1;
 	match->kvm = kvm;
 	match->ack_notifier.irq_acked = kvm_assigned_dev_ack_irq;
@@ -868,7 +868,7 @@ static int kvm_vm_ioctl_set_pci_irq_mask(struct kvm *kvm,
 		goto out;
 	}
 
-	mutex_lock(&match->intx_mask_lock);
+	spin_lock(&match->intx_mask_lock);
 
 	match->flags &= ~KVM_DEV_ASSIGN_MASK_INTX;
 	match->flags |= assigned_dev->flags & KVM_DEV_ASSIGN_MASK_INTX;
@@ -895,7 +895,7 @@ static int kvm_vm_ioctl_set_pci_irq_mask(struct kvm *kvm,
 		}
 	}
 
-	mutex_unlock(&match->intx_mask_lock);
+	spin_unlock(&match->intx_mask_lock);
 
 out:
 	mutex_unlock(&kvm->lock);
-- 
1.7.3.4

Re: [PATCH] KVM: Convert intx_mask_lock to spin lock

[Marcelo Tosatti]

On Wed, Mar 14, 2012 at 11:02:11AM +0100, Jan Kiszka wrote:
> As kvm_notify_acked_irq calls kvm_assigned_dev_ack_irq under
> rcu_read_lock, we cannot use a mutex in the latter function. Switch to a
> spin lock to address this.
> 
> Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
> ---
>  include/linux/kvm_host.h |    2 +-
>  virt/kvm/assigned-dev.c  |   14 +++++++-------
>  2 files changed, 8 insertions(+), 8 deletions(-)

Applied, thanks.