linux-kernel - Re: [PATCH] vdpa/mlx5: Use write memory barrier after updating CQ index

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Date:   Mon, 7 Dec 2020 10:51:44 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Eli Cohen <elic@...dia.com>, mst@...hat.com,
        virtualization@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org
Cc:     lulu@...hat.com
Subject: Re: [PATCH] vdpa/mlx5: Use write memory barrier after updating CQ
 index


On 2020/12/6 下午6:57, Eli Cohen wrote:
> Make sure to put 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.
>
> Change-Id: Ib0ae4c118cce524c9f492b32569179f3c1f04cc1
> Fixes: 1a86b377aa21 ("vdpa/mlx5: Add VDPA driver for supported mlx5 devices")
> Signed-off-by: Eli Cohen <elic@...dia.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 1f4089c6f9d7..295f46eea2a5 100644
> --- a/drivers/vdpa/mlx5/net/mlx5_vnet.c
> +++ b/drivers/vdpa/mlx5/net/mlx5_vnet.c
> @@ -478,6 +478,11 @@ 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.
> +	 */
> +	wmb();
>   	rx_post(&mvq->vqqp, num);
>   	if (mvq->event_cb.callback)
>   		mvq->event_cb.callback(mvq->event_cb.private);


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