netdev - Re: [PATCH 3/3] mlx5_vdpa: defer clear_virtqueues to until DRIVER

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Date:   Mon, 8 Feb 2021 07:48:16 +0200
From:   Eli Cohen <elic@...dia.com>
To:     Si-Wei Liu <si-wei.liu@...cle.com>
CC:     <mst@...hat.com>, <jasowang@...hat.com>,
        <linux-kernel@...r.kernel.org>,
        <virtualization@...ts.linux-foundation.org>,
        <netdev@...r.kernel.org>
Subject: Re: [PATCH 3/3] mlx5_vdpa: defer clear_virtqueues to until DRIVER_OK

On Sat, Feb 06, 2021 at 04:29:24AM -0800, Si-Wei Liu wrote:
> While virtq is stopped,  get_vq_state() is supposed to
> be  called to  get  sync'ed  with  the latest internal
> avail_index from device. The saved avail_index is used
> to restate  the virtq  once device is started.  Commit
> b35ccebe3ef7 introduced the clear_virtqueues() routine
> to  reset  the saved  avail_index,  however, the index
> gets cleared a bit earlier before get_vq_state() tries
> to read it. This would cause consistency problems when
> virtq is restarted, e.g. through a series of link down
> and link up events. We  could  defer  the  clearing of
> avail_index  to  until  the  device  is to be started,
> i.e. until  VIRTIO_CONFIG_S_DRIVER_OK  is set again in
> set_status().


Not sure I understand the scenario. You are talking about reset of the
device followed by up/down events on the interface. How can you trigger
this?

> 
> Fixes: b35ccebe3ef7 ("vdpa/mlx5: Restore the hardware used index after change map")
> Signed-off-by: Si-Wei Liu <si-wei.liu@...cle.com>
> ---
>  drivers/vdpa/mlx5/net/mlx5_vnet.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/vdpa/mlx5/net/mlx5_vnet.c b/drivers/vdpa/mlx5/net/mlx5_vnet.c
> index aa6f8cd..444ab58 100644
> --- a/drivers/vdpa/mlx5/net/mlx5_vnet.c
> +++ b/drivers/vdpa/mlx5/net/mlx5_vnet.c
> @@ -1785,7 +1785,6 @@ static void mlx5_vdpa_set_status(struct vdpa_device *vdev, u8 status)
>  	if (!status) {
>  		mlx5_vdpa_info(mvdev, "performing device reset\n");
>  		teardown_driver(ndev);
> -		clear_virtqueues(ndev);
>  		mlx5_vdpa_destroy_mr(&ndev->mvdev);
>  		ndev->mvdev.status = 0;
>  		++mvdev->generation;
> @@ -1794,6 +1793,7 @@ static void mlx5_vdpa_set_status(struct vdpa_device *vdev, u8 status)
>  
>  	if ((status ^ ndev->mvdev.status) & VIRTIO_CONFIG_S_DRIVER_OK) {
>  		if (status & VIRTIO_CONFIG_S_DRIVER_OK) {
> +			clear_virtqueues(ndev);
>  			err = setup_driver(ndev);
>  			if (err) {
>  				mlx5_vdpa_warn(mvdev, "failed to setup driver\n");
> -- 
> 1.8.3.1
>