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>

1 files changed, 12 insertions, 42 deletions

diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index 448efe01f18a..9a9502a4aa50 100644
--- 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;
         }