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

From: Jason Wang <[email-masked]>
Date: Wed, 19 Nov 2014 17:21:46 +0800

On 11/19/2014 04:54 PM, Cornelia Huck wrote:
> On Wed, 19 Nov 2014 15:21:29 +0800
> Jason Wang <[email-masked]> 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
>> ---
>>  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)) {
> Do an early return, get rid of one indentation level?

This sounds good.
>> +		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",
> s/hyperviser/hypervisor/ (also below)

Yes, thanks for the catching.
>
>> +					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,
>> +	};
> I'm wondering whether it would be easier to read if you listed all
> prereqs per feature instead of all features that depend on a feature?
> It would still be hard to express the v4/v6 or conditions below in
> tables, though.

For v4 and v6, we could use something like

unsigned int feature_for_host_tso6[] = {
VIRTIO_NET_F_HOST_ECN,
};

unsigned int feature_for_host_tso4[] = {
VIRTIO_NET_F_HOST_ECN,
}

To avoid the following open-coding for ECN. And probably we need another
device specific dependency table and let virtio core do this instead.
>
> Or call the arrays features_depending_on_foo?

Yes.
>
>> +	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;
> If you already print a message that a user may use to fix their
> hypervisor (or bug someone about it), would it make sense to check all
> dependencies and print a full list of everything that is broken in the
> advertised feature bits? I usually hate it if I fix one thing only to
> hit the next bug when the program could have already told me about
> everything I need to fix :)
>

Right this sounds good.
>> +
>> +	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",
> "Hypervisor bug: advertised feature <foo> but not <bar> or <baz>"
>
> ?

More compact, looks good. Thanks