vhost: fix packed ring descriptor update in async enqueue

If the packet uses multiple descriptors and its descriptor indices are
wrapped, the first descriptor flag is not updated last, which may cause
virtio read the incomplete packet. For example, given a packet uses 64
descriptors, and virtio ring size is 256, and its descriptor indices are
224~255 and 0~31, current implementation will update 224~255 descriptor
flags earlier than 0~31 descriptor flags.

This patch fixes this issue by updating descriptor flags in one loop,
so that the first descriptor flag is always updated last.

Fixes: 873e8dad6f49 ("vhost: support packed ring in async datapath")
Signed-off-by: Jiayu Hu <jiayu.hu@intel.com>
Reviewed-by: Chenbo Xia <chenbo.xia@intel.com>
Reviewed-by: Maxime Coquelin <maxime.coquelin@redhat.com>

diff --git a/lib/vhost/virtio_net.c b/lib/vhost/virtio_net.c
index cef4bcf15c2e7ba631368f62ed407536a1eeecbe..b3d954aab4b0df5210be62f42eb0232f35246e4d 100644 (file)
--- a/lib/vhost/virtio_net.c
+++ b/lib/vhost/virtio_net.c
@@ -1549,60 +1549,6 @@ virtio_dev_rx_async_submit_split(struct virtio_net *dev,
        return pkt_idx;
 }
 
-static __rte_always_inline void
-vhost_update_used_packed(struct vhost_virtqueue *vq,
-                       struct vring_used_elem_packed *shadow_ring,
-                       uint16_t count)
-{
-       int i;
-       uint16_t used_idx = vq->last_used_idx;
-       uint16_t head_idx = vq->last_used_idx;
-       uint16_t head_flags = 0;
-
-       if (count == 0)
-               return;
-
-       /* Split loop in two to save memory barriers */
-       for (i = 0; i < count; i++) {
-               vq->desc_packed[used_idx].id = shadow_ring[i].id;
-               vq->desc_packed[used_idx].len = shadow_ring[i].len;
-
-               used_idx += shadow_ring[i].count;
-               if (used_idx >= vq->size)
-                       used_idx -= vq->size;
-       }
-
-       /* The ordering for storing desc flags needs to be enforced. */
-       rte_atomic_thread_fence(__ATOMIC_RELEASE);
-
-       for (i = 0; i < count; i++) {
-               uint16_t flags;
-
-               if (vq->shadow_used_packed[i].len)
-                       flags = VRING_DESC_F_WRITE;
-               else
-                       flags = 0;
-
-               if (vq->used_wrap_counter) {
-                       flags |= VRING_DESC_F_USED;
-                       flags |= VRING_DESC_F_AVAIL;
-               } else {
-                       flags &= ~VRING_DESC_F_USED;
-                       flags &= ~VRING_DESC_F_AVAIL;
-               }
-
-               if (i > 0) {
-                       vq->desc_packed[vq->last_used_idx].flags = flags;
-               } else {
-                       head_idx = vq->last_used_idx;
-                       head_flags = flags;
-               }
-
-               vq_inc_last_used_packed(vq, shadow_ring[i].count);
-       }
-
-       vq->desc_packed[head_idx].flags = head_flags;
-}
 
 static __rte_always_inline int
 vhost_enqueue_async_packed(struct virtio_net *dev,
@@ -1819,23 +1765,63 @@ write_back_completed_descs_packed(struct vhost_virtqueue *vq,
                                uint16_t n_buffers)
 {
        struct vhost_async *async = vq->async;
-       uint16_t nr_left = n_buffers;
-       uint16_t from, to;
+       uint16_t from = async->last_buffer_idx_packed;
+       uint16_t used_idx = vq->last_used_idx;
+       uint16_t head_idx = vq->last_used_idx;
+       uint16_t head_flags = 0;
+       uint16_t i;
 
-       do {
-               from = async->last_buffer_idx_packed;
-               to = (from + nr_left) % vq->size;
-               if (to > from) {
-                       vhost_update_used_packed(vq, async->buffers_packed + from, to - from);
-                       async->last_buffer_idx_packed += nr_left;
-                       nr_left = 0;
+       /* Split loop in two to save memory barriers */
+       for (i = 0; i < n_buffers; i++) {
+               vq->desc_packed[used_idx].id = async->buffers_packed[from].id;
+               vq->desc_packed[used_idx].len = async->buffers_packed[from].len;
+
+               used_idx += async->buffers_packed[from].count;
+               if (used_idx >= vq->size)
+                       used_idx -= vq->size;
+
+               from++;
+               if (from >= vq->size)
+                       from = 0;
+       }
+
+       /* The ordering for storing desc flags needs to be enforced. */
+       rte_atomic_thread_fence(__ATOMIC_RELEASE);
+
+       from = async->last_buffer_idx_packed;
+
+       for (i = 0; i < n_buffers; i++) {
+               uint16_t flags;
+
+               if (async->buffers_packed[from].len)
+                       flags = VRING_DESC_F_WRITE;
+               else
+                       flags = 0;
+
+               if (vq->used_wrap_counter) {
+                       flags |= VRING_DESC_F_USED;
+                       flags |= VRING_DESC_F_AVAIL;
                } else {
-                       vhost_update_used_packed(vq, async->buffers_packed + from,
-                               vq->size - from);
-                       async->last_buffer_idx_packed = 0;
-                       nr_left -= vq->size - from;
+                       flags &= ~VRING_DESC_F_USED;
+                       flags &= ~VRING_DESC_F_AVAIL;
                }
-       } while (nr_left > 0);
+
+               if (i > 0) {
+                       vq->desc_packed[vq->last_used_idx].flags = flags;
+               } else {
+                       head_idx = vq->last_used_idx;
+                       head_flags = flags;
+               }
+
+               vq_inc_last_used_packed(vq, async->buffers_packed[from].count);
+
+               from++;
+               if (from == vq->size)
+                       from = 0;
+       }
+
+       vq->desc_packed[head_idx].flags = head_flags;
+       async->last_buffer_idx_packed = from;
 }
 
 static __rte_always_inline uint16_t