diff --git a/virt/kvm/eventfd.c b/virt/kvm/eventfd.c
index c1f1e3c..2ca4535 100644
--- a/virt/kvm/eventfd.c
+++ b/virt/kvm/eventfd.c
@@ -44,14 +44,19 @@
  */
 
 struct _irqfd {
-	struct kvm               *kvm;
-	struct eventfd_ctx       *eventfd;
-	int                       gsi;
-	struct list_head          list;
-	poll_table                pt;
-	wait_queue_t              wait;
-	struct work_struct        inject;
-	struct work_struct        shutdown;
+	/* Used for MSI fast-path */
+	struct kvm *kvm;
+	wait_queue_t wait;
+	/* Update side is protected by irqfds.lock */
+	struct kvm_kernel_irq_routing_entry __rcu *irq_entry;
+	/* Used for level IRQ fast-path */
+	int gsi;
+	struct work_struct inject;
+	/* Used for setup/shutdown */
+	struct eventfd_ctx *eventfd;
+	struct list_head list;
+	poll_table pt;
+	struct work_struct shutdown;
 };
 
 static struct workqueue_struct *irqfd_cleanup_wq;
@@ -125,14 +130,22 @@
 {
 	struct _irqfd *irqfd = container_of(wait, struct _irqfd, wait);
 	unsigned long flags = (unsigned long)key;
+	struct kvm_kernel_irq_routing_entry *irq;
+	struct kvm *kvm = irqfd->kvm;
 
-	if (flags & POLLIN)
+	if (flags & POLLIN) {
+		rcu_read_lock();
+		irq = rcu_dereference(irqfd->irq_entry);
 		/* An event has been signaled, inject an interrupt */
-		schedule_work(&irqfd->inject);
+		if (irq)
+			kvm_set_msi(irq, kvm, KVM_USERSPACE_IRQ_SOURCE_ID, 1);
+		else
+			schedule_work(&irqfd->inject);
+		rcu_read_unlock();
+	}
 
 	if (flags & POLLHUP) {
 		/* The eventfd is closing, detach from KVM */
-		struct kvm *kvm = irqfd->kvm;
 		unsigned long flags;
 
 		spin_lock_irqsave(&kvm->irqfds.lock, flags);
@@ -163,9 +176,31 @@
 	add_wait_queue(wqh, &irqfd->wait);
 }
 
+/* Must be called under irqfds.lock */
+static void irqfd_update(struct kvm *kvm, struct _irqfd *irqfd,
+			 struct kvm_irq_routing_table *irq_rt)
+{
+	struct kvm_kernel_irq_routing_entry *e;
+	struct hlist_node *n;
+
+	if (irqfd->gsi >= irq_rt->nr_rt_entries) {
+		rcu_assign_pointer(irqfd->irq_entry, NULL);
+		return;
+	}
+
+	hlist_for_each_entry(e, n, &irq_rt->map[irqfd->gsi], link) {
+		/* Only fast-path MSI. */
+		if (e->type == KVM_IRQ_ROUTING_MSI)
+			rcu_assign_pointer(irqfd->irq_entry, e);
+		else
+			rcu_assign_pointer(irqfd->irq_entry, NULL);
+	}
+}
+
 static int
 kvm_irqfd_assign(struct kvm *kvm, int fd, int gsi)
 {
+	struct kvm_irq_routing_table *irq_rt;
 	struct _irqfd *irqfd, *tmp;
 	struct file *file = NULL;
 	struct eventfd_ctx *eventfd = NULL;
@@ -215,6 +250,10 @@
 		goto fail;
 	}
 
+	irq_rt = rcu_dereference_protected(kvm->irq_routing,
+					   lockdep_is_held(&kvm->irqfds.lock));
+	irqfd_update(kvm, irqfd, irq_rt);
+
 	events = file->f_op->poll(file, &irqfd->pt);
 
 	list_add_tail(&irqfd->list, &kvm->irqfds.items);
@@ -271,8 +310,17 @@
 	spin_lock_irq(&kvm->irqfds.lock);
 
 	list_for_each_entry_safe(irqfd, tmp, &kvm->irqfds.items, list) {
-		if (irqfd->eventfd == eventfd && irqfd->gsi == gsi)
+		if (irqfd->eventfd == eventfd && irqfd->gsi == gsi) {
+			/*
+			 * This rcu_assign_pointer is needed for when
+			 * another thread calls kvm_irqfd_update before
+			 * we flush workqueue below.
+			 * It is paired with synchronize_rcu done by caller
+			 * of that function.
+			 */
+			rcu_assign_pointer(irqfd->irq_entry, NULL);
 			irqfd_deactivate(irqfd);
+		}
 	}
 
 	spin_unlock_irq(&kvm->irqfds.lock);
@@ -322,6 +370,25 @@
 }
 
 /*
+ * Change irq_routing and irqfd.
+ * Caller must invoke synchronize_rcu afterwards.
+ */
+void kvm_irq_routing_update(struct kvm *kvm,
+			    struct kvm_irq_routing_table *irq_rt)
+{
+	struct _irqfd *irqfd;
+
+	spin_lock_irq(&kvm->irqfds.lock);
+
+	rcu_assign_pointer(kvm->irq_routing, irq_rt);
+
+	list_for_each_entry(irqfd, &kvm->irqfds.items, list)
+		irqfd_update(kvm, irqfd, irq_rt);
+
+	spin_unlock_irq(&kvm->irqfds.lock);
+}
+
+/*
  * create a host-wide workqueue for issuing deferred shutdown requests
  * aggregated from all vm* instances. We need our own isolated single-thread
  * queue to prevent deadlock against flushing the normal work-queue.