vhost: generalize adding used elem

Use one generic vhost_copy_to_user() instead of two dedicated
accessor. This will simplify the conversion to fine grain
accessors. About 2% improvement of PPS were seen during vitio-user
txonly test.

Signed-off-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index 3f3eac4..3fb5801 100644 (file)
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -2273,16 +2273,7 @@ static int __vhost_add_used_n(struct vhost_virtqueue *vq,
 
        start = vq->last_used_idx & (vq->num - 1);
        used = vq->used->ring + start;
-       if (count == 1) {
-               if (vhost_put_user(vq, heads[0].id, &used->id)) {
-                       vq_err(vq, "Failed to write used id");
-                       return -EFAULT;
-               }
-               if (vhost_put_user(vq, heads[0].len, &used->len)) {
-                       vq_err(vq, "Failed to write used len");
-                       return -EFAULT;
-               }
-       } else if (vhost_copy_to_user(vq, used, heads, count * sizeof *used)) {
+       if (vhost_copy_to_user(vq, used, heads, count * sizeof *used)) {
                vq_err(vq, "Failed to write used");
                return -EFAULT;
        }