[UNTESTED] KVM: do not call kvm_set_irq from irq disabled section

[Marcelo Tosatti <mtosatti@redhat.com>]

The assigned device interrupt work handler calls kvm_set_irq, which
can sleep, for example, waiting for the ioapic mutex, from irq disabled
section.

https://bugzilla.kernel.org/show_bug.cgi?id=15725

Fix by dropping assigned_dev_lock (and re-enabling interrupts)
before invoking kvm_set_irq for the KVM_DEV_IRQ_HOST_MSIX case. Other
cases do not require the lock or interrupts disabled (a new work
instance will be queued in case of concurrent interrupt).

KVM-Stable-Tag.
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

diff --git a/virt/kvm/assigned-dev.c b/virt/kvm/assigned-dev.c
index 47ca447..7ac7bbe 100644
--- a/virt/kvm/assigned-dev.c
+++ b/virt/kvm/assigned-dev.c
@@ -64,24 +64,33 @@ static void kvm_assigned_dev_interrupt_work_handler(struct work_struct *work)
 				    interrupt_work);
 	kvm = assigned_dev->kvm;
 
-	spin_lock_irq(&assigned_dev->assigned_dev_lock);
 	if (assigned_dev->irq_requested_type & KVM_DEV_IRQ_HOST_MSIX) {
 		struct kvm_guest_msix_entry *guest_entries =
 			assigned_dev->guest_msix_entries;
+
+		spin_lock_irq(&assigned_dev->assigned_dev_lock);
 		for (i = 0; i < assigned_dev->entries_nr; i++) {
 			if (!(guest_entries[i].flags &
 					KVM_ASSIGNED_MSIX_PENDING))
 				continue;
 			guest_entries[i].flags &= ~KVM_ASSIGNED_MSIX_PENDING;
+			/*
+ 			 * If kvm_assigned_dev_intr sets pending for an
+ 			 * entry smaller than this work instance is
+ 			 * currently processing, a new work instance
+ 			 * will be queued.
+ 			 */
+			spin_unlock_irq(&assigned_dev->assigned_dev_lock);
 			kvm_set_irq(assigned_dev->kvm,
 				    assigned_dev->irq_source_id,
 				    guest_entries[i].vector, 1);
+			spin_lock_irq(&assigned_dev->assigned_dev_lock);
 		}
+		spin_unlock_irq(&assigned_dev->assigned_dev_lock);
 	} else
 		kvm_set_irq(assigned_dev->kvm, assigned_dev->irq_source_id,
 			    assigned_dev->guest_irq, 1);
 
-	spin_unlock_irq(&assigned_dev->assigned_dev_lock);
 }
 
 static irqreturn_t kvm_assigned_dev_intr(int irq, void *dev_id)