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

From: Jason Wang <[email-masked]>
Date: Wed, 19 Nov 2014 17:33:26 +0800

On 11/19/2014 04:59 PM, Michael S. Tsirkin wrote:
> On Wed, Nov 19, 2014 at 02:35:39PM +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]>
>> ---
>>  drivers/net/virtio_net.c | 93 ++++++++++++++++++++++++++++++++++++++++++++++++
>>  1 file changed, 93 insertions(+)
>>
>> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
>> index ec2a8b4..4a0ad46 100644
>> --- a/drivers/net/virtio_net.c
>> +++ b/drivers/net/virtio_net.c
>> @@ -1673,6 +1673,95 @@ 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",
>
> This line's way too long.

Yes. (Anyway it pass checkpatch.pl since it forbids quoted string to be
split)
>
>> +					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,
>> +		VIRTIO_NET_F_GUEST_UFO,
>> +	};
>> +	unsigned int features_for_host_csum[] = {
>> +		VIRTIO_NET_F_HOST_TSO4,
>> +		VIRTIO_NET_F_HOST_TSO6,
>> +		VIRTIO_NET_F_HOST_ECN,
>> +		VIRTIO_NET_F_HOST_UFO,
>> +	};
>> +	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 +1769,10 @@ 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,
> The API seems too complex, and you still had to open-code ECN logic.
> Just open-code most of it. 

Yes, the ECN could be done through the same way as ctrl_vq did.

How about move those checking into virtio core by just letting device
export its dependency table?
>  You can use a helper macro to output a
> friendly message without code duplication.
> For example like the below (completely untested)?
>
>
> I would also like to split things: dependencies on
> VIRTIO_NET_F_CTRL_VQ might go into this kernel,
> since they help fix BUG.
>
> Others should wait since they don't fix any crashes, and there's a small
> chance of a regression for some hypervisor in the field.

Probably ok but not sure, since the rest features are all related to
csum and offloading, we are in fact depends on network core to fix them.
>
> -->
>
> virtio-net: friendlier handling of misconfigured hypervisors
>
> We currently trigger BUG when VIRTIO_NET_F_CTRL_VQ
> is not set but one of features depending on it is.
> That's not a friendly way to report errors to
> hypervisors.
> Let's check, and fail probe instead.
>
> Signed-off-by: Michael S. Tsirkin <[email-masked]>
>
> ---
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 26e1330..7a7d1a3 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -1673,6 +1673,21 @@ static const struct attribute_group virtio_net_mrg_rx_group = {
>  };
>  #endif
>  
> +bool __virtnet_fail_on_feature(struct virtio_device *vdev, unsigned int fbit,
> +			       const char *fname)
> +{
> +	if (!virtio_has_feature(vdev, fbit))
> +		return false;
> +
> +        dev_err(&dev->dev, "missing requirements for feature bit %d: %s\n",
> +		fbit, fname);
> +
> +	return true;
> +}
> +
> +#define VIRTNET_FAIL_ON(vdev, fbit) \
> +	__virtnet_fail_on_feature(vdev, fbit, #fbit)
> +
>  static int virtnet_probe(struct virtio_device *vdev)
>  {
>  	int i, err;
> @@ -1680,6 +1695,14 @@ static int virtnet_probe(struct virtio_device *vdev)
>  	struct virtnet_info *vi;
>  	u16 max_queue_pairs;
>  
> +	if (!virtio_has_feature(vdev, VIRTIO_NET_F_CTRL_VQ) &&
> +		(VIRTNET_FAIL_ON(vdev, VIRTIO_NET_F_CTRL_RX) ||
> +		 VIRTNET_FAIL_ON(vdev, VIRTIO_NET_F_CTRL_VLAN) ||
> +		 VIRTNET_FAIL_ON(vdev, VIRTIO_NET_F_GUEST_ANNOUNCE) ||
> +		 VIRTNET_FAIL_ON(vdev, VIRTIO_NET_F_MQ) ||
> +		 VIRTNET_FAIL_ON(vdev, VIRTIO_NET_F_CTRL_MAC_ADDR)))
> +		return -EINVAL;
> +
>  	/* Find if host supports multiqueue virtio_net device */
>  	err = virtio_cread_feature(vdev, VIRTIO_NET_F_MQ,
>  				   struct virtio_net_config,
>

Patch looks good, but consider we may check more dependencies in the
future, may need a helper instead. Or just use this and switch to
dependency table in 3.19.