Re: [dpdk-dev] [PATCH] vhost: prevent disabled rings to be processed with zero-copy

[Tiwei Bie <tiwei.bie@intel.com>]

On Wed, Feb 27, 2019 at 09:54:28AM +0100, Maxime Coquelin wrote:
> The vhost-user spec says that once the vring is disabled, the
> client has to stop processing it. But it can happen when
> dequeue zero-copy is enabled if outstanding descriptors buffers
> are still being processed by an extranl NIC or another guest.

s/extranl/external/

> 
> The fix consists in draining the zmbufs list to ensure no more
> descriptors buffers are in the wild.
> 
> Note that this fix is only working in the case REPLY_ACK
> protocol feature is enabled, which is not the case by default
> for now (it is only enabled when IOMMU feature is enabled in
> the vhost library).
> 
> Fixes: b0a985d1f340 ("vhost: add dequeue zero copy")
> Cc: stable@dpdk.org
> 
> Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com>
> ---
>  lib/librte_vhost/vhost_user.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/lib/librte_vhost/vhost_user.c b/lib/librte_vhost/vhost_user.c
> index 36c0c676d..ef947b90c 100644
> --- a/lib/librte_vhost/vhost_user.c
> +++ b/lib/librte_vhost/vhost_user.c
> @@ -1336,6 +1336,10 @@ vhost_user_set_vring_enable(struct virtio_net **pdev,
>  		"set queue enable: %d to qp idx: %d\n",
>  		enable, index);
>  
> +	/* On disable, rings have to be stopped being processed. */
> +	if (!enable && dev->dequeue_zero_copy)
> +		drain_zmbuf_list(dev->virtqueue[index]);

It might be better to drain the zmbufs list after calling
application's vring_state_changed() callback, so there will
be a chance for applications to take some actions first if
they want.

Overall this looks good to me,

Reviewed-by: Tiwei Bie <tiwei.bie@intel.com>

Thanks!
Tiwei