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From: "Michael S. Tsirkin" <mst@redhat.com>
To: Eli Cohen <elic@nvidia.com>
Cc: linux-kernel@vger.kernel.org, lulu@redhat.com,
	virtualization@lists.linux-foundation.org
Subject: Re: [PATCH] vdpa/mlx5: Use write memory barrier after updating CQ index
Date: Tue, 8 Dec 2020 16:45:04 -0500	[thread overview]
Message-ID: <20201208164356-mutt-send-email-mst@kernel.org> (raw)
In-Reply-To: <20201206105719.123753-1-elic@nvidia.com>

On Sun, Dec 06, 2020 at 12:57:19PM +0200, 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@nvidia.com>

Aren't both memory writes? And given that, isn't dma_wmb() sufficient
here?


> ---
>  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);
> -- 
> 2.27.0

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WARNING: multiple messages have this Message-ID (diff)
From: "Michael S. Tsirkin" <mst@redhat.com>
To: Eli Cohen <elic@nvidia.com>
Cc: jasowang@redhat.com, virtualization@lists.linux-foundation.org,
	linux-kernel@vger.kernel.org, lulu@redhat.com
Subject: Re: [PATCH] vdpa/mlx5: Use write memory barrier after updating CQ index
Date: Tue, 8 Dec 2020 16:45:04 -0500	[thread overview]
Message-ID: <20201208164356-mutt-send-email-mst@kernel.org> (raw)
In-Reply-To: <20201206105719.123753-1-elic@nvidia.com>

On Sun, Dec 06, 2020 at 12:57:19PM +0200, 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@nvidia.com>

Aren't both memory writes? And given that, isn't dma_wmb() sufficient
here?


> ---
>  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);
> -- 
> 2.27.0


  parent reply	other threads:[~2020-12-08 21:45 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-12-06 10:57 [PATCH] vdpa/mlx5: Use write memory barrier after updating CQ index Eli Cohen
2020-12-07  2:51 ` Jason Wang
2020-12-07  2:51   ` Jason Wang
2020-12-08  9:15   ` Eli Cohen
2020-12-08 13:53     ` Michael S. Tsirkin
2020-12-08 13:53       ` Michael S. Tsirkin
2020-12-08 21:45 ` Michael S. Tsirkin [this message]
2020-12-08 21:45   ` Michael S. Tsirkin
2020-12-09  6:02   ` Eli Cohen
2020-12-09  6:46     ` Michael S. Tsirkin
2020-12-09  6:46       ` Michael S. Tsirkin
2020-12-09  6:58       ` Eli Cohen
2020-12-09  8:05         ` Michael S. Tsirkin
2020-12-09  8:05           ` Michael S. Tsirkin
2020-12-09  9:38           ` Eli Cohen
2020-12-09 12:47             ` Michael S. Tsirkin
2020-12-09 12:47               ` Michael S. Tsirkin

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