1 files changed, 12 insertions, 9 deletions

diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index 1ca88908723b..fb06570ae951 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -89,9 +89,6 @@ struct vring_virtqueue
 	/* Number we've added since last sync. */
 	unsigned int num_added;
 
-	/* Last used index we've seen. */
-	u16 last_used_idx;
-
 	/* How to notify other side. FIXME: commonalize hcalls! */
 	void (*notify)(struct virtqueue *vq);
 
@@ -285,12 +282,13 @@ static void detach_buf(struct vring_virtqueue *vq, unsigned int head)
 
 static inline bool more_used(const struct vring_virtqueue *vq)
 {
-	return vq->last_used_idx != vq->vring.used->idx;
+	return *vq->vring.last_used_idx != vq->vring.used->idx;
 }
 
 void *virtqueue_get_buf(struct virtqueue *_vq, unsigned int *len)
 {
 	struct vring_virtqueue *vq = to_vvq(_vq);
+	struct vring_used_elem *u;
 	void *ret;
 	unsigned int i;
 
@@ -310,9 +308,9 @@ void *virtqueue_get_buf(struct virtqueue *_vq, unsigned int *len)
 	/* Only get used array entries after they have been exposed by host. */
 	virtio_rmb();
 
-	i = vq->vring.used->ring[vq->last_used_idx%vq->vring.num].id;
-	*len = vq->vring.used->ring[vq->last_used_idx%vq->vring.num].len;
-
+	u = &vq->vring.used->ring[*vq->vring.last_used_idx % vq->vring.num];
+	i = u->id;
+	*len = u->len;
 	if (unlikely(i >= vq->vring.num)) {
 		BAD_RING(vq, "id %u out of range\n", i);
 		return NULL;
@@ -325,7 +323,8 @@ void *virtqueue_get_buf(struct virtqueue *_vq, unsigned int *len)
 	/* detach_buf clears data, so grab it now. */
 	ret = vq->data[i];
 	detach_buf(vq, i);
-	vq->last_used_idx++;
+	(*vq->vring.last_used_idx)++;
+
 	END_USE(vq);
 	return ret;
 }
@@ -348,6 +347,8 @@ bool virtqueue_enable_cb(struct virtqueue *_vq)
 	/* We optimistically turn back on interrupts, then check if there was
 	 * more to do. */
 	vq->vring.avail->flags &= ~VRING_AVAIL_F_NO_INTERRUPT;
+	/* Besides flags write, this barrier also flushes out
+	 * last available index write. */
 	virtio_mb();
 	if (unlikely(more_used(vq))) {
 		END_USE(vq);
@@ -431,7 +432,7 @@ struct virtqueue *vring_new_virtqueue(unsigned int num,
 	vq->vq.name = name;
 	vq->notify = notify;
 	vq->broken = false;
-	vq->last_used_idx = 0;
+	*vq->vring.last_used_idx = 0;
 	vq->num_added = 0;
 	list_add_tail(&vq->vq.list, &vdev->vqs);
 #ifdef DEBUG
@@ -473,6 +474,8 @@ void vring_transport_features(struct virtio_device *vdev)
 		switch (i) {
 		case VIRTIO_RING_F_INDIRECT_DESC:
 			break;
+		case VIRTIO_RING_F_PUBLISH_USED:
+			break;
 		default:
 			/* We don't understand this bit. */
 			clear_bit(i, vdev->features);