vhost-net: mergeable buffers support

This adds support for mergeable buffers in vhost-net: this is needed
for older guests without indirect buffer support, as well
as for zero copy with some devices.

Includes changes by Michael S. Tsirkin to make the
patch as low risk as possible (i.e., close to no changes
when feature is disabled).

Signed-off-by: David Stevens <dlstevens@us.ibm.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

1 files changed, 75 insertions, 4 deletions

diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index dd2d019b889f..e05557d52999 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -149,7 +149,8 @@ static void vhost_vq_reset(struct vhost_dev *dev,
 	vq->used_flags = 0;
 	vq->log_used = false;
 	vq->log_addr = -1ull;
-	vq->hdr_size = 0;
+	vq->vhost_hlen = 0;
+	vq->sock_hlen = 0;
 	vq->private_data = NULL;
 	vq->log_base = NULL;
 	vq->error_ctx = NULL;
@@ -1101,9 +1102,9 @@ int vhost_get_vq_desc(struct vhost_dev *dev, struct vhost_virtqueue *vq,
 }
 
 /* Reverse the effect of vhost_get_vq_desc. Useful for error handling. */
-void vhost_discard_vq_desc(struct vhost_virtqueue *vq)
+void vhost_discard_vq_desc(struct vhost_virtqueue *vq, int n)
 {
-	vq->last_avail_idx--;
+	vq->last_avail_idx -= n;
 }
 
 /* After we've used one of their buffers, we tell them about it.  We'll then
@@ -1148,6 +1149,67 @@ int vhost_add_used(struct vhost_virtqueue *vq, unsigned int head, int len)
 	return 0;
 }
 
+static int __vhost_add_used_n(struct vhost_virtqueue *vq,
+			    struct vring_used_elem *heads,
+			    unsigned count)
+{
+	struct vring_used_elem __user *used;
+	int start;
+
+	start = vq->last_used_idx % vq->num;
+	used = vq->used->ring + start;
+	if (copy_to_user(used, heads, count * sizeof *used)) {
+		vq_err(vq, "Failed to write used");
+		return -EFAULT;
+	}
+	if (unlikely(vq->log_used)) {
+		/* Make sure data is seen before log. */
+		smp_wmb();
+		/* Log used ring entry write. */
+		log_write(vq->log_base,
+			  vq->log_addr +
+			   ((void __user *)used - (void __user *)vq->used),
+			  count * sizeof *used);
+	}
+	vq->last_used_idx += count;
+	return 0;
+}
+
+/* After we've used one of their buffers, we tell them about it.  We'll then
+ * want to notify the guest, using eventfd. */
+int vhost_add_used_n(struct vhost_virtqueue *vq, struct vring_used_elem *heads,
+		     unsigned count)
+{
+	int start, n, r;
+
+	start = vq->last_used_idx % vq->num;
+	n = vq->num - start;
+	if (n < count) {
+		r = __vhost_add_used_n(vq, heads, n);
+		if (r < 0)
+			return r;
+		heads += n;
+		count -= n;
+	}
+	r = __vhost_add_used_n(vq, heads, count);
+
+	/* Make sure buffer is written before we update index. */
+	smp_wmb();
+	if (put_user(vq->last_used_idx, &vq->used->idx)) {
+		vq_err(vq, "Failed to increment used idx");
+		return -EFAULT;
+	}
+	if (unlikely(vq->log_used)) {
+		/* Log used index update. */
+		log_write(vq->log_base,
+			  vq->log_addr + offsetof(struct vring_used, idx),
+			  sizeof vq->used->idx);
+		if (vq->log_ctx)
+			eventfd_signal(vq->log_ctx, 1);
+	}
+	return r;
+}
+
 /* This actually signals the guest, using eventfd. */
 void vhost_signal(struct vhost_dev *dev, struct vhost_virtqueue *vq)
 {
@@ -1182,6 +1244,15 @@ void vhost_add_used_and_signal(struct vhost_dev *dev,
 	vhost_signal(dev, vq);
 }
 
+/* multi-buffer version of vhost_add_used_and_signal */
+void vhost_add_used_and_signal_n(struct vhost_dev *dev,
+				 struct vhost_virtqueue *vq,
+				 struct vring_used_elem *heads, unsigned count)
+{
+	vhost_add_used_n(vq, heads, count);
+	vhost_signal(dev, vq);
+}
+
 /* OK, now we need to know about added descriptors. */
 bool vhost_enable_notify(struct vhost_virtqueue *vq)
 {
@@ -1206,7 +1277,7 @@ bool vhost_enable_notify(struct vhost_virtqueue *vq)
 		return false;
 	}
 
-	return avail_idx != vq->last_avail_idx;
+	return avail_idx != vq->avail_idx;
 }
 
 /* We don't need to be notified again. */