2 files changed, 52 insertions, 12 deletions

diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index 6ea92a6d1134..c56bbe799241 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -262,19 +262,22 @@ add_head:
 EXPORT_SYMBOL_GPL(virtqueue_add_buf);
 
 /**
- * virtqueue_kick - update after add_buf
+ * virtqueue_kick_prepare - first half of split virtqueue_kick call.
  * @vq: the struct virtqueue
  *
- * After one or more virtqueue_add_buf calls, invoke this to kick
- * the other side.
+ * Instead of virtqueue_kick(), you can do:
+ *      if (virtqueue_kick_prepare(vq))
+ *              virtqueue_notify(vq);
  *
- * Caller must ensure we don't call this with other virtqueue
- * operations at the same time (except where noted).
+ * This is sometimes useful because the virtqueue_kick_prepare() needs
+ * to be serialized, but the actual virtqueue_notify() call does not.
  */
-void virtqueue_kick(struct virtqueue *_vq)
+bool virtqueue_kick_prepare(struct virtqueue *_vq)
 {
         struct vring_virtqueue *vq = to_vvq(_vq);
         u16 new, old;
+        bool needs_kick;
+
         START_USE(vq);
         /* Descriptors and available array need to be set before we expose the
          * new available array entries. */
@@ -287,13 +290,46 @@ void virtqueue_kick(struct virtqueue *_vq)
         /* Need to update avail index before checking if we should notify */
         virtio_mb(vq);
 
-        if (vq->event ?
-            vring_need_event(vring_avail_event(&vq->vring), new, old) :
-            !(vq->vring.used->flags & VRING_USED_F_NO_NOTIFY))
-                /* Prod other side to tell it about changes. */
-                vq->notify(&vq->vq);
-
+        if (vq->event) {
+                needs_kick = vring_need_event(vring_avail_event(&vq->vring),
+                                              new, old);
+        } else {
+                needs_kick = !(vq->vring.used->flags & VRING_USED_F_NO_NOTIFY);
+        }
         END_USE(vq);
+        return needs_kick;
+}
+EXPORT_SYMBOL_GPL(virtqueue_kick_prepare);
+
+/**
+ * virtqueue_notify - second half of split virtqueue_kick call.
+ * @vq: the struct virtqueue
+ *
+ * This does not need to be serialized.
+ */
+void virtqueue_notify(struct virtqueue *_vq)
+{
+        struct vring_virtqueue *vq = to_vvq(_vq);
+
+        /* Prod other side to tell it about changes. */
+        vq->notify(_vq);
+}
+EXPORT_SYMBOL_GPL(virtqueue_notify);
+
+/**
+ * virtqueue_kick - update after add_buf
+ * @vq: the struct virtqueue
+ *
+ * After one or more virtqueue_add_buf calls, invoke this to kick
+ * the other side.
+ *
+ * Caller must ensure we don't call this with other virtqueue
+ * operations at the same time (except where noted).
+ */
+void virtqueue_kick(struct virtqueue *vq)
+{
+        if (virtqueue_kick_prepare(vq))
+                virtqueue_notify(vq);
 }
 EXPORT_SYMBOL_GPL(virtqueue_kick);
 
diff --git a/include/linux/virtio.h b/include/linux/virtio.h
index ec1706e7df50..31fe3a62874b 100644
--- a/include/linux/virtio.h
+++ b/include/linux/virtio.h
@@ -34,6 +34,10 @@ int virtqueue_add_buf(struct virtqueue *vq,
 
 void virtqueue_kick(struct virtqueue *vq);
 
+bool virtqueue_kick_prepare(struct virtqueue *vq);
+
+void virtqueue_notify(struct virtqueue *vq);
+
 void *virtqueue_get_buf(struct virtqueue *vq, unsigned int *len);
 
 void virtqueue_disable_cb(struct virtqueue *vq);