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

From: "Michael S. Tsirkin" <[email-masked]>
Date: Wed, 19 Nov 2014 11:39:01 +0200

On Wed, Nov 19, 2014 at 05:33:26PM +0800, Jason Wang wrote:
> 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?

So far we only have this for net, let's not add
one-off APIs.

> >  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.

Well it does fix them so ... there's no bug, is there?

> >
> > -->
> >
> > 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. 

Pls note this is just pseudo-code - I didn't even compile it.
If you want something like this merged, go ahead and
post it, probably addressing Cornelia's request to
print the dependency too. Maybe:

> >		(VIRTNET_FAIL_ON(vdev, VIRTIO_NET_F_CTRL_RX, "ctrl_vq") ||
> >		 VIRTNET_FAIL_ON(vdev, VIRTIO_NET_F_CTRL_VLAN, "ctrl_vq") ||
> >		 VIRTNET_FAIL_ON(vdev, VIRTIO_NET_F_GUEST_ANNOUNCE, "ctrl_vq") ||
> >		 VIRTNET_FAIL_ON(vdev, VIRTIO_NET_F_MQ, "ctrl_vq") ||
> >		 VIRTNET_FAIL_ON(vdev, VIRTIO_NET_F_CTRL_MAC_ADDR, "ctrl_vq")))

-- 
MST