vhost: switch to use vhost_add_used_n()

Let vhost_add_used() to use vhost_add_used_n() to reduce the code
duplication. To avoid the overhead brought by __copy_to_user(). We will use
put_user() when one used need to be added.

Signed-off-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index 448efe01f18a173d8d560fc68387d9393d415a62..9a9502a4aa5089519d338ca62b07a557069fb00d 100644 (file)
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -1332,48 +1332,9 @@ EXPORT_SYMBOL_GPL(vhost_discard_vq_desc);
  * want to notify the guest, using eventfd. */
 int vhost_add_used(struct vhost_virtqueue *vq, unsigned int head, int len)
 {
-       struct vring_used_elem __user *used;
+       struct vring_used_elem heads = { head, len };
 
-       /* The virtqueue contains a ring of used buffers.  Get a pointer to the
-        * next entry in that used ring. */
-       used = &vq->used->ring[vq->last_used_idx % vq->num];
-       if (__put_user(head, &used->id)) {
-               vq_err(vq, "Failed to write used id");
-               return -EFAULT;
-       }
-       if (__put_user(len, &used->len)) {
-               vq_err(vq, "Failed to write used len");
-               return -EFAULT;
-       }
-       /* Make sure buffer is written before we update index. */
-       smp_wmb();
-       if (__put_user(vq->last_used_idx + 1, &vq->used->idx)) {
-               vq_err(vq, "Failed to increment used idx");
-               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),
-                         sizeof *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);
-       }
-       vq->last_used_idx++;
-       /* If the driver never bothers to signal in a very long while,
-        * used index might wrap around. If that happens, invalidate
-        * signalled_used index we stored. TODO: make sure driver
-        * signals at least once in 2^16 and remove this. */
-       if (unlikely(vq->last_used_idx == vq->signalled_used))
-               vq->signalled_used_valid = false;
-       return 0;
+       return vhost_add_used_n(vq, &heads, 1);
 }
 EXPORT_SYMBOL_GPL(vhost_add_used);
 
@@ -1387,7 +1348,16 @@ static int __vhost_add_used_n(struct vhost_virtqueue *vq,
 
        start = vq->last_used_idx % vq->num;
        used = vq->used->ring + start;
-       if (__copy_to_user(used, heads, count * sizeof *used)) {
+       if (count == 1) {
+               if (__put_user(heads[0].id, &used->id)) {
+                       vq_err(vq, "Failed to write used id");
+                       return -EFAULT;
+               }
+               if (__put_user(heads[0].len, &used->len)) {
+                       vq_err(vq, "Failed to write used len");
+                       return -EFAULT;
+               }
+       } else if (__copy_to_user(used, heads, count * sizeof *used)) {
                vq_err(vq, "Failed to write used");
                return -EFAULT;
        }