On 8/25/23 19:01, Ilya Maximets wrote:
> It was supposed to be a compiler barrier and it was a compiler barrier
> initially called 'wmb' (??) when virtio core support was introduced.
> Later all the instances of 'wmb' were switched to smp_wmb to fix memory
> ordering issues on non-x86 platforms. However, this one doesn't need
> to be an actual barrier. It's enough for it to stay a compiler barrier
> as its only purpose is to ensure that the value is not read twice.
>
> There is no counterpart read barrier in the drivers, AFAICT. And even
> if we needed an actual barrier, it shouldn't have been a write barrier.
>
> Signed-off-by: Ilya Maximets <i.maxim...@ovn.org>
> ---
Kind reminder.
Best regards, Ilya Maximets.
> hw/virtio/virtio.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
> index 309038fd46..6eb8586858 100644
> --- a/hw/virtio/virtio.c
> +++ b/hw/virtio/virtio.c
> @@ -1051,7 +1051,7 @@ static int virtqueue_split_read_next_desc(VirtIODevice
> *vdev, VRingDesc *desc,
> /* Check they're not leading us off end of descriptors. */
> *next = desc->next;
> /* Make sure compiler knows to grab that: we don't want it changing! */
> - smp_wmb();
> + barrier();
>
> if (*next >= max) {
> virtio_error(vdev, "Desc next is %u", *next);
