linux-kernel - RE: [PATCH v1 1/1] platform/mellanox: mlxbf-tmfifo: Fix a memory barrier issue

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Date:   Fri, 7 May 2021 15:38:43 +0000
From:   Vadim Pasternak <vadimp@...dia.com>
To:     Liming Sun <limings@...dia.com>,
        Andy Shevchenko <andy@...radead.org>,
        Darren Hart <dvhart@...radead.org>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "platform-driver-x86@...r.kernel.org" 
        <platform-driver-x86@...r.kernel.org>
Subject: RE: [PATCH v1 1/1] platform/mellanox: mlxbf-tmfifo: Fix a memory
 barrier issue



> -----Original Message-----
> From: Liming Sun <limings@...dia.com>
> Sent: Friday, May 7, 2021 6:19 PM
> To: Andy Shevchenko <andy@...radead.org>; Darren Hart
> <dvhart@...radead.org>; Vadim Pasternak <vadimp@...dia.com>
> Cc: Liming Sun <limings@...dia.com>; linux-kernel@...r.kernel.org;
> platform-driver-x86@...r.kernel.org
> Subject: [PATCH v1 1/1] platform/mellanox: mlxbf-tmfifo: Fix a memory
> barrier issue
> 
> The virtio framework uses wmb() when updating avail->idx. It guarantees
> the write order, but not necessarily loading order for the code accessing the
> memory. This commit adds a load barrier after reading the avail->idx to make
> sure all the data in the descriptor is visible. It also adds a barrier when
> returning the packet to virtio framework to make sure read/writes are visible
> to the virtio code.

I suppose it should be sent as Bugfix?

> 
> Signed-off-by: Liming Sun <limings@...dia.com>
> ---
>  drivers/platform/mellanox/mlxbf-tmfifo.c | 11 ++++++++++-
>  1 file changed, 10 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/platform/mellanox/mlxbf-tmfifo.c
> b/drivers/platform/mellanox/mlxbf-tmfifo.c
> index bbc4e71..38800e8 100644
> --- a/drivers/platform/mellanox/mlxbf-tmfifo.c
> +++ b/drivers/platform/mellanox/mlxbf-tmfifo.c
> @@ -294,6 +294,9 @@ static irqreturn_t mlxbf_tmfifo_irq_handler(int irq,
> void *arg)
>  	if (vring->next_avail == virtio16_to_cpu(vdev, vr->avail->idx))
>  		return NULL;
> 
> +	/* Make sure 'avail->idx' is visible already. */
> +	virtio_rmb(false);
> +
>  	idx = vring->next_avail % vr->num;
>  	head = virtio16_to_cpu(vdev, vr->avail->ring[idx]);
>  	if (WARN_ON(head >= vr->num))
> @@ -322,7 +325,7 @@ static void mlxbf_tmfifo_release_desc(struct
> mlxbf_tmfifo_vring *vring,
>  	 * done or not. Add a memory barrier here to make sure the update
> above
>  	 * completes before updating the idx.
>  	 */
> -	mb();
> +	virtio_mb(false);
>  	vr->used->idx = cpu_to_virtio16(vdev, vr_idx + 1);  }
> 
> @@ -733,6 +736,12 @@ static bool mlxbf_tmfifo_rxtx_one_desc(struct
> mlxbf_tmfifo_vring *vring,
>  		desc = NULL;
>  		fifo->vring[is_rx] = NULL;
> 
> +		/*
> +		 * Make sure the load/store are in order before
> +		 * returning back to virtio.
> +		 */
> +		virtio_mb(false);
> +
>  		/* Notify upper layer that packet is done. */
>  		spin_lock_irqsave(&fifo->spin_lock[is_rx], flags);
>  		vring_interrupt(0, vring->vq);
> --
> 1.8.3.1