Subject: Re: [PATCH V2 net] virtio-net: validate features during probe

From: "Michael S. Tsirkin" <[email-masked]>
Date: Wed, 19 Nov 2014 11:01:09 +0200

On Wed, Nov 19, 2014 at 03:21:29PM +0800, Jason Wang wrote:
> This patch validates feature dependencies during probe and fail the probing
> if a dependency is missed. This fixes the issues of hitting BUG()
> when qemu fails to advertise features correctly. One example is booting
> guest with ctrl_vq=off through qemu.
> 
> Cc: Rusty Russell <[email-masked]>
> Cc: Michael S. Tsirkin <[email-masked]>
> Cc: Cornelia Huck <[email-masked]>
> Cc: Wanlong Gao <[email-masked]>
> Signed-off-by: Jason Wang <[email-masked]>
> ---
> Changes from V1:
> - Drop VIRTIO_NET_F_*_UFO from the checklist, since it was disabled

In this form, it's not 3.18 material anyway.
Let's just focus on fixing BUG that you see for now,
and for 3.19, let's fix UFO.

> ---
>  drivers/net/virtio_net.c | 91 ++++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 91 insertions(+)
> 
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index ec2a8b4..b16a761 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -1673,6 +1673,93 @@ static const struct attribute_group virtio_net_mrg_rx_group = {
>  };
>  #endif
>  
> +static int virtnet_validate_features(struct virtio_device *dev,
> +				     unsigned int *table,
> +				     int table_size,
> +				     unsigned int feature)
> +{
> +	int i;
> +
> +	if (!virtio_has_feature(dev, feature)) {
> +		for (i = 0; i < table_size; i++) {
> +			unsigned int f = table[i];
> +
> +			if (virtio_has_feature(dev, f)) {
> +				dev_err(&dev->dev,
> +					"buggy hyperviser: feature 0x%x was advertised but its dependency 0x%x was not",
> +					f, feature);
> +				return -EINVAL;
> +			}
> +		}
> +	}
> +
> +	return 0;
> +}
> +
> +static int virtnet_check_features(struct virtio_device *dev)
> +{
> +	unsigned int features_for_ctrl_vq[] = {
> +		VIRTIO_NET_F_CTRL_RX,
> +		VIRTIO_NET_F_CTRL_VLAN,
> +		VIRTIO_NET_F_GUEST_ANNOUNCE,
> +		VIRTIO_NET_F_MQ,
> +		VIRTIO_NET_F_CTRL_MAC_ADDR
> +	};
> +	unsigned int features_for_guest_csum[] = {
> +		VIRTIO_NET_F_GUEST_TSO4,
> +		VIRTIO_NET_F_GUEST_TSO6,
> +		VIRTIO_NET_F_GUEST_ECN,
> +	};
> +	unsigned int features_for_host_csum[] = {
> +		VIRTIO_NET_F_HOST_TSO4,
> +		VIRTIO_NET_F_HOST_TSO6,
> +		VIRTIO_NET_F_HOST_ECN,
> +	};
> +	int err;
> +
> +	err = virtnet_validate_features(dev, features_for_ctrl_vq,
> +					ARRAY_SIZE(features_for_ctrl_vq),
> +					VIRTIO_NET_F_CTRL_VQ);
> +	if (err)
> +		return err;
> +
> +	err = virtnet_validate_features(dev, features_for_guest_csum,
> +					ARRAY_SIZE(features_for_guest_csum),
> +					VIRTIO_NET_F_GUEST_CSUM);
> +	if (err)
> +		return err;
> +
> +	err = virtnet_validate_features(dev, features_for_host_csum,
> +					ARRAY_SIZE(features_for_host_csum),
> +					VIRTIO_NET_F_CSUM);
> +	if (err)
> +		return err;
> +
> +	if (virtio_has_feature(dev, VIRTIO_NET_F_GUEST_ECN) &&
> +	    (!virtio_has_feature(dev, VIRTIO_NET_F_GUEST_TSO4) ||
> +	     !virtio_has_feature(dev, VIRTIO_NET_F_GUEST_TSO6))) {
> +		dev_err(&dev->dev,
> +			"buggy hyperviser: feature 0x%x was advertised but its dependency 0x%x or 0x%x was not",
> +			VIRTIO_NET_F_GUEST_ECN,
> +			VIRTIO_NET_F_GUEST_TSO4,
> +			VIRTIO_NET_F_GUEST_TSO6);
> +		return -EINVAL;
> +	}
> +
> +	if (virtio_has_feature(dev, VIRTIO_NET_F_HOST_ECN) &&
> +	    (!virtio_has_feature(dev, VIRTIO_NET_F_HOST_TSO4) ||
> +	     !virtio_has_feature(dev, VIRTIO_NET_F_HOST_TSO6))) {
> +		dev_err(&dev->dev,
> +			"buggy hyperviser: feature 0x%x was advertised but its dependency 0x%x or 0x%x was not",
> +			VIRTIO_NET_F_HOST_ECN,
> +			VIRTIO_NET_F_HOST_TSO4,
> +			VIRTIO_NET_F_HOST_TSO6);
> +		return -EINVAL;
> +	}
> +
> +	return 0;
> +}
> +
>  static int virtnet_probe(struct virtio_device *vdev)
>  {
>  	int i, err;
> @@ -1680,6 +1767,10 @@ static int virtnet_probe(struct virtio_device *vdev)
>  	struct virtnet_info *vi;
>  	u16 max_queue_pairs;
>  
> +	err = virtnet_check_features(vdev);
> +	if (err)
> +		return -EINVAL;
> +
>  	/* Find if host supports multiqueue virtio_net device */
>  	err = virtio_cread_feature(vdev, VIRTIO_NET_F_MQ,
>  				   struct virtio_net_config,
> -- 
> 1.9.1