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Subject: Re: [PATCH] vdpa/mlx5: should keep avail_index despite device status
To:     Si-Wei Liu <si-wei.liu@oracle.com>, netdev@vger.kernel.org,
        mst@redhat.com
Cc:     joao.m.martins@oracle.com, boris.ostrovsky@oracle.com,
        linux-kernel@vger.kernel.org,
        virtualization@lists.linux-foundation.org
References: <1601583511-15138-1-git-send-email-si-wei.liu@oracle.com>
From:   Jason Wang <jasowang@redhat.com>
Message-ID: <f3d1af9e-9164-dd42-1de4-7a40da46abba@redhat.com>
Date:   Sat, 10 Oct 2020 15:31:51 +0800
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On 2020/10/2 上午4:18, Si-Wei Liu wrote:
> A VM with mlx5 vDPA has below warnings while being reset:
>
> vhost VQ 0 ring restore failed: -1: Resource temporarily unavailable (11)
> vhost VQ 1 ring restore failed: -1: Resource temporarily unavailable (11)
>
> We should allow userspace emulating the virtio device be
> able to get to vq's avail_index, regardless of vDPA device
> status. Save the index that was last seen when virtq was
> stopped, so that userspace doesn't complain.
>
> Signed-off-by: Si-Wei Liu <si-wei.liu@oracle.com>


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


> ---
>   drivers/vdpa/mlx5/net/mlx5_vnet.c | 20 ++++++++++++++------
>   1 file changed, 14 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/vdpa/mlx5/net/mlx5_vnet.c b/drivers/vdpa/mlx5/net/mlx5_vnet.c
> index 70676a6..74264e59 100644
> --- a/drivers/vdpa/mlx5/net/mlx5_vnet.c
> +++ b/drivers/vdpa/mlx5/net/mlx5_vnet.c
> @@ -1133,15 +1133,17 @@ static void suspend_vq(struct mlx5_vdpa_net *ndev, struct mlx5_vdpa_virtqueue *m
>   	if (!mvq->initialized)
>   		return;
>   
> -	if (query_virtqueue(ndev, mvq, &attr)) {
> -		mlx5_vdpa_warn(&ndev->mvdev, "failed to query virtqueue\n");
> -		return;
> -	}
>   	if (mvq->fw_state != MLX5_VIRTIO_NET_Q_OBJECT_STATE_RDY)
>   		return;
>   
>   	if (modify_virtqueue(ndev, mvq, MLX5_VIRTIO_NET_Q_OBJECT_STATE_SUSPEND))
>   		mlx5_vdpa_warn(&ndev->mvdev, "modify to suspend failed\n");
> +
> +	if (query_virtqueue(ndev, mvq, &attr)) {
> +		mlx5_vdpa_warn(&ndev->mvdev, "failed to query virtqueue\n");
> +		return;
> +	}
> +	mvq->avail_idx = attr.available_index;
>   }
>   
>   static void suspend_vqs(struct mlx5_vdpa_net *ndev)
> @@ -1411,8 +1413,14 @@ static int mlx5_vdpa_get_vq_state(struct vdpa_device *vdev, u16 idx, struct vdpa
>   	struct mlx5_virtq_attr attr;
>   	int err;
>   
> -	if (!mvq->initialized)
> -		return -EAGAIN;
> +	/* If the virtq object was destroyed, use the value saved at
> +	 * the last minute of suspend_vq. This caters for userspace
> +	 * that cares about emulating the index after vq is stopped.
> +	 */
> +	if (!mvq->initialized) {
> +		state->avail_index = mvq->avail_idx;
> +		return 0;
> +	}
>   
>   	err = query_virtqueue(ndev, mvq, &attr);
>   	if (err) {