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Subject: Re: [PATCH v1] vdpa/mlx5: Use write memory barrier after updating CQ
 index
To:     Eli Cohen <elic@nvidia.com>, mst@redhat.com,
        virtualization@lists.linux-foundation.org,
        linux-kernel@vger.kernel.org
Cc:     lulu@redhat.com, maxime.coquelin@redhat.com
References: <20201209140004.15892-1-elic@nvidia.com>
From:   Jason Wang <jasowang@redhat.com>
Message-ID: <26dd1676-ff63-4940-9b0d-d7097950c1e5@redhat.com>
Date:   Thu, 10 Dec 2020 17:11:02 +0800
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On 2020/12/9 下午10:00, Eli Cohen wrote:
> Make sure to put dma write memory barrier after updating CQ consumer
> index so the hardware knows that there are available CQE slots in the
> queue.
>
> Failure to do this can cause the update of the RX doorbell record to get
> updated before the CQ consumer index resulting in CQ overrun.
>
> Fixes: 1a86b377aa21 ("vdpa/mlx5: Add VDPA driver for supported mlx5 devices")
> Signed-off-by: Eli Cohen <elic@nvidia.com>
> ---
> V0 -> V1
> Use dma_wmb() instead of wmb()


Acked-by: Jason Wang <jasowang@redhat.com>


>
>   drivers/vdpa/mlx5/net/mlx5_vnet.c | 5 +++++
>   1 file changed, 5 insertions(+)
>
> diff --git a/drivers/vdpa/mlx5/net/mlx5_vnet.c b/drivers/vdpa/mlx5/net/mlx5_vnet.c
> index db87abc3cb60..43b0069ff8b1 100644
> --- a/drivers/vdpa/mlx5/net/mlx5_vnet.c
> +++ b/drivers/vdpa/mlx5/net/mlx5_vnet.c
> @@ -479,6 +479,11 @@ static int mlx5_vdpa_poll_one(struct mlx5_vdpa_cq *vcq)
>   static void mlx5_vdpa_handle_completions(struct mlx5_vdpa_virtqueue *mvq, int num)
>   {
>   	mlx5_cq_set_ci(&mvq->cq.mcq);
> +
> +	/* make sure CQ cosumer update is visible to the hardware before updating
> +	 * RX doorbell record.
> +	 */
> +	dma_wmb();
>   	rx_post(&mvq->vqqp, num);
>   	if (mvq->event_cb.callback)
>   		mvq->event_cb.callback(mvq->event_cb.private);