On 05.12.2018 12:49, Maxime Coquelin wrote:
> A read barrier is required to ensure that the ordering between
> descriptor's flags and content reads is enforced.
>
> Fixes: 2f3225a7d69b ("vhost: add vector filling support for packed ring")
> Cc: sta...@dpdk.org
>
> Reported-by: Jason Wang <jasow...@redhat.com>
> Signed-off-by: Maxime Coquelin <maxime.coque...@redhat.com>
> ---
> lib/librte_vhost/virtio_net.c | 6 ++++++
> 1 file changed, 6 insertions(+)
>
> diff --git a/lib/librte_vhost/virtio_net.c b/lib/librte_vhost/virtio_net.c
> index f11ebb54f..68b72e7a5 100644
> --- a/lib/librte_vhost/virtio_net.c
> +++ b/lib/librte_vhost/virtio_net.c
> @@ -520,6 +520,12 @@ fill_vec_buf_packed(struct virtio_net *dev, struct
> vhost_virtqueue *vq,
> if (unlikely(!desc_is_avail(&descs[avail_idx], wrap_counter)))
> return -1;
>
> + /*
> + * The ordering between desc flags and desc
> + * content reads need to be enforced.
> + */
> + rte_smp_rmb();
> +
Same here. 'desc_is_avail' reads and uses the flags. i.e.
no way for reordering,
Writes must be ordered on the virtio side by the write barrier.
This means that if flags are updated (desc_is_avail() == true)
than the whole descriptor already updated and the data is written.
No need to have any read barriers here.
> *desc_count = 0;
> *len = 0;
>
>
