The virtqueue_kick() operation really has two phases and should be split
so that devices hold locks only when necessary. This patch splits
virtqueue_kick() into two virtqueue_kick_prepare() and
virtqueue_kick_notify().
virtqueue_kick_prepare() updates the vring and checks whether the host
needs to be notified. This function must be executed with a lock held
to protect the vring.
virtqueue_kick_notify() notifies the host that the vring has new
buffers. This function may be executed without holding a lock
protecting the vring.
Signed-off-by: Stefan Hajnoczi <stefanha@xxxxxxxxxxxxxxxxxx>
---
drivers/virtio/virtio_ring.c | 28 +++++++++++++++++++++-------
include/linux/virtio.h | 13 +++++++++++++
2 files changed, 34 insertions(+), 7 deletions(-)
diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index 68b9136..7d059f7 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -237,10 +237,12 @@ add_head:
}
EXPORT_SYMBOL_GPL(virtqueue_add_buf_gfp);
-void virtqueue_kick(struct virtqueue *_vq)
+bool virtqueue_kick_prepare(struct virtqueue *_vq)
{
struct vring_virtqueue *vq = to_vvq(_vq);
u16 new, old;
+ bool r;
+
START_USE(vq);
/* Descriptors and available array need to be set before we expose the
* new available array entries. */
@@ -253,13 +255,25 @@ void virtqueue_kick(struct virtqueue *_vq)
/* Need to update avail index before checking if we should notify */
virtio_mb();
- 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)
+ r = vring_need_event(vring_avail_event(&vq->vring), new, old);
+ else
+ r = !(vq->vring.used->flags & VRING_USED_F_NO_NOTIFY);
END_USE(vq);
+ return r;
+}
+EXPORT_SYMBOL_GPL(virtqueue_kick_prepare);
+
+void virtqueue_kick_notify(struct virtqueue *_vq)
+{
+ to_vvq(_vq)->notify(_vq);
+}
+EXPORT_SYMBOL_GPL(virtqueue_kick_notify);
+
+void virtqueue_kick(struct virtqueue *_vq)
+{
+ if (virtqueue_kick_prepare(_vq))
+ virtqueue_kick_notify(_vq);
}
EXPORT_SYMBOL_GPL(virtqueue_kick);
diff --git a/include/linux/virtio.h b/include/linux/virtio.h
index 7108857..65536cb 100644
--- a/include/linux/virtio.h
+++ b/include/linux/virtio.h
@@ -35,9 +35,18 @@ struct virtqueue {
* data: the token identifying the buffer.
* gfp: how to do memory allocations (if necessary).
* Returns remaining capacity of queue (sg segments) or a negative error.
+ * virtqueue_kick_prepare: update after add_buf and check if kick necessary
+ * vq: the struct virtqueue
+ * After one or more add_buf calls, invoke this to check whether kick is
+ * necessary.
+ * virtqueue_kick_notify: kick the other side
+ * vq: the struct virtqueue
+ * Normally virtqueue_kick_prepare is called before this. Can be done in
+ * parallel with add_buf/get_buf.
* virtqueue_kick: update after add_buf
* vq: the struct virtqueue
* After one or more add_buf calls, invoke this to kick the other side.
+ * Uses virtqueue_kick_prepare and virtqueue_kick_notify internally.
* virtqueue_get_buf: get the next used buffer
* vq: the struct virtqueue we're talking about.
* len: the length written into the buffer
@@ -85,6 +94,10 @@ static inline int virtqueue_add_buf(struct virtqueue *vq,
return virtqueue_add_buf_gfp(vq, sg, out_num, in_num, data, GFP_ATOMIC);
}
+bool virtqueue_kick_prepare(struct virtqueue *vq);
+
+void virtqueue_kick_notify(struct virtqueue *vq);
+
void virtqueue_kick(struct virtqueue *vq);
void *virtqueue_get_buf(struct virtqueue *vq, unsigned int *len);
--
1.7.5.4
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