Reading the used->flags could be reordered with avail->idx update.
vhost in kernel disables notifications for the time of packets
receiving, like this:
1. disable notify
2. process packets
3. enable notify
4. has more packets ? goto 1
In case of reordering, virtio driver could read the flags on
step 2 while notifications disabled and update avail->idx after
the step 4, i.e. vhost will exit the loop on step 4 with
notifications enabled, but virtio will not notify.
Fixes: c1f86306a026 ("virtio: add new driver")
CC: sta...@dpdk.org
Reported-by: Shahaf Shuler <shah...@mellanox.com>
Signed-off-by: Ilya Maximets <i.maxim...@samsung.com>
---
drivers/net/virtio/virtqueue.h | 8 ++++++++
1 file changed, 8 insertions(+)
diff --git a/drivers/net/virtio/virtqueue.h b/drivers/net/virtio/virtqueue.h
index d8ae5cdec..dffa03669 100644
--- a/drivers/net/virtio/virtqueue.h
+++ b/drivers/net/virtio/virtqueue.h
@@ -415,6 +415,11 @@ vq_update_avail_ring(struct virtqueue *vq, uint16_t
desc_idx)
static inline int
virtqueue_kick_prepare(struct virtqueue *vq)
{
+ /*
+ * Ensure updated avail->idx is visible to vhost before reading
+ * the used->flags.
+ */
+ virtio_mb();
return !(vq->vq_ring.used->flags & VRING_USED_F_NO_NOTIFY);
}
@@ -423,6 +428,9 @@ virtqueue_kick_prepare_packed(struct virtqueue *vq)
{
uint16_t flags;
+ /*
+ * Ensure updated data is visible to vhost before reading the flags.
+ */
virtio_mb();
flags = vq->ring_packed.device_event->desc_event_flags;
--
2.17.1
