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From: Gregory Haskins <ghaskins@novell.com>
Subject: [KVM PATCH v3 3/3] KVM: Directly inject interrupts if they support
	lockless operation
To: kvm@vger.kernel.org
Cc: alacrityvm-devel@lists.sourceforge.net, linux-kernel@vger.kernel.org
Date: Mon, 26 Oct 2009 12:22:08 -0400
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diff --git a/virt/kvm/eventfd.c b/virt/kvm/eventfd.c
index 30f70fd..e6cc958 100644
--- a/virt/kvm/eventfd.c
+++ b/virt/kvm/eventfd.c
@@ -51,20 +51,34 @@ struct _irqfd {
 	wait_queue_t              wait;
 	struct work_struct        inject;
 	struct work_struct        shutdown;
+	void (*execute)(struct _irqfd *);
 };
 
 static struct workqueue_struct *irqfd_cleanup_wq;
 
 static void
-irqfd_inject(struct work_struct *work)
+irqfd_inject(struct _irqfd *irqfd)
 {
-	struct _irqfd *irqfd = container_of(work, struct _irqfd, inject);
 	struct kvm *kvm = irqfd->kvm;
 
 	kvm_set_irq(kvm, KVM_USERSPACE_IRQ_SOURCE_ID, irqfd->gsi, 1);
 	kvm_set_irq(kvm, KVM_USERSPACE_IRQ_SOURCE_ID, irqfd->gsi, 0);
 }
 
+static void
+irqfd_deferred_inject(struct work_struct *work)
+{
+	struct _irqfd *irqfd = container_of(work, struct _irqfd, inject);
+
+	irqfd_inject(irqfd);
+}
+
+static void
+irqfd_schedule(struct _irqfd *irqfd)
+{
+	schedule_work(&irqfd->inject);
+}
+
 /*
  * Race-free decouple logic (ordering is critical)
  */
@@ -126,7 +140,7 @@ irqfd_wakeup(wait_queue_t *wait, unsigned mode, int sync, void *key)
 
 	if (flags & POLLIN)
 		/* An event has been signaled, inject an interrupt */
-		schedule_work(&irqfd->inject);
+		irqfd->execute(irqfd);
 
 	if (flags & POLLHUP) {
 		/* The eventfd is closing, detach from KVM */
@@ -179,7 +193,7 @@ kvm_irqfd_assign(struct kvm *kvm, int fd, int gsi)
 	irqfd->kvm = kvm;
 	irqfd->gsi = gsi;
 	INIT_LIST_HEAD(&irqfd->list);
-	INIT_WORK(&irqfd->inject, irqfd_inject);
+	INIT_WORK(&irqfd->inject, irqfd_deferred_inject);
 	INIT_WORK(&irqfd->shutdown, irqfd_shutdown);
 
 	file = eventfd_fget(fd);
@@ -209,6 +223,15 @@ kvm_irqfd_assign(struct kvm *kvm, int fd, int gsi)
 	list_add_tail(&irqfd->list, &kvm->irqfds.items);
 	spin_unlock_irq(&kvm->irqfds.lock);
 
+	ret = kvm_irq_check_lockless(kvm, gsi);
+	if (ret < 0)
+		goto fail;
+
+	if (ret)
+		irqfd->execute = &irqfd_inject;
+	else
+		irqfd->execute = &irqfd_schedule;
+
 	/*
 	 * Check if there was an event already pending on the eventfd
 	 * before we registered, and trigger it as if we didn't miss it.