Subject: Re: [PATCH v2 3/3] vduse: Temporarily disable control queue features

From: "Michael S. Tsirkin" <[email-masked]>
Date: Tue, 4 Jul 2023 12:43:20 -0400

On Tue, Jul 04, 2023 at 06:40:45PM +0200, Maxime Coquelin wrote:
> Virtio-net driver control queue implementation is not safe
> when used with VDUSE. If the VDUSE application does not
> reply to control queue messages, it currently ends up
> hanging the kernel thread sending this command.
> 
> Some work is on-going to make the control queue
> implementation robust with VDUSE. Until it is completed,
> let's disable control virtqueue and features that depend on
> it.
> 
> Signed-off-by: Maxime Coquelin <[email-masked]>
> ---
>  drivers/vdpa/vdpa_user/vduse_dev.c | 21 +++++++++++++++++++++
>  1 file changed, 21 insertions(+)
> 
> diff --git a/drivers/vdpa/vdpa_user/vduse_dev.c b/drivers/vdpa/vdpa_user/vduse_dev.c
> index 1271c9796517..04367a53802b 100644
> --- a/drivers/vdpa/vdpa_user/vduse_dev.c
> +++ b/drivers/vdpa/vdpa_user/vduse_dev.c
> @@ -1778,6 +1778,25 @@ static struct attribute *vduse_dev_attrs[] = {
>  
>  ATTRIBUTE_GROUPS(vduse_dev);
>  
> +static void vduse_dev_features_fixup(struct vduse_dev_config *config)
> +{
> +	if (config->device_id == VIRTIO_ID_NET) {
> +		/*
> +		 * Temporarily disable control virtqueue and features that
> +		 * depend on it while CVQ is being made more robust for VDUSE.
> +		 */
> +		config->features &= ~((1ULL << VIRTIO_NET_F_CTRL_VQ) |
> +				(1ULL << VIRTIO_NET_F_CTRL_RX) |
> +				(1ULL << VIRTIO_NET_F_CTRL_VLAN) |
> +				(1ULL << VIRTIO_NET_F_GUEST_ANNOUNCE) |
> +				(1ULL << VIRTIO_NET_F_MQ) |
> +				(1ULL << VIRTIO_NET_F_CTRL_MAC_ADDR) |
> +				(1ULL << VIRTIO_NET_F_RSS) |
> +				(1ULL << VIRTIO_NET_F_HASH_REPORT) |
> +				(1ULL << VIRTIO_NET_F_NOTF_COAL));
> +	}
> +}
> +

This will never be exhaustive, we are adding new features.
Please add an allowlist with just legal ones instead.

>  static int vduse_create_dev(struct vduse_dev_config *config,
>  			    void *config_buf, u64 api_version)
>  {
> @@ -1793,6 +1812,8 @@ static int vduse_create_dev(struct vduse_dev_config *config,
>  	if (!dev)
>  		goto err;
>  
> +	vduse_dev_features_fixup(config);
> +
>  	dev->api_version = api_version;
>  	dev->device_features = config->features;
>  	dev->device_id = config->device_id;
> -- 
> 2.41.0