Re: [PATCH net v3] virtio_net: Do not send RSS key if it is not supported

[Heng Qi]

在 2024/4/1 上午4:20, Michael S. Tsirkin 写道:
> On Fri, Mar 29, 2024 at 10:16:41AM -0700, Breno Leitao wrote:
> > There is a bug when setting the RSS options in virtio_net that can break
> > the whole machine, getting the kernel into an infinite loop.
> >
> > Running the following command in any QEMU virtual machine with virtionet
> > will reproduce this problem:
> >
> >      # ethtool -X eth0  hfunc toeplitz
> >
> > This is how the problem happens:
> >
> > 1) ethtool_set_rxfh() calls virtnet_set_rxfh()
> >
> > 2) virtnet_set_rxfh() calls virtnet_commit_rss_command()
> >
> > 3) virtnet_commit_rss_command() populates 4 entries for the rss
> > scatter-gather
> >
> > 4) Since the command above does not have a key, then the last
> > scatter-gatter entry will be zeroed, since rss_key_size == 0.
> > sg_buf_size = vi->rss_key_size;
> >
> > 5) This buffer is passed to qemu, but qemu is not happy with a buffer
> > with zero length, and do the following in virtqueue_map_desc() (QEMU
> > function):
> >
> >    if (!sz) {
> >        virtio_error(vdev, "virtio: zero sized buffers are not allowed");
> >
> > 6) virtio_error() (also QEMU function) set the device as broken
> >
> >      vdev->broken = true;
> >
> > 7) Qemu bails out, and do not repond this crazy kernel.
> >
> > 8) The kernel is waiting for the response to come back (function
> > virtnet_send_command())
> >
> > 9) The kernel is waiting doing the following :
> >
> >        while (!virtqueue_get_buf(vi->cvq, &tmp) &&
> > 	     !virtqueue_is_broken(vi->cvq))
> > 	      cpu_relax();
> >
> > 10) None of the following functions above is true, thus, the kernel
> > loops here forever. Keeping in mind that virtqueue_is_broken() does
> > not look at the qemu `vdev->broken`, so, it never realizes that the
> > vitio is broken at QEMU side.
> >
> > Fix it by not sending RSS commands if the feature is not available in
> > the device.
> >
> > Fixes: c7114b1249fa ("drivers/net/virtio_net: Added basic RSS support.")
> > Cc: stable@xxxxxxxxxxxxxxx
> net has its own stable process, don't CC stable on net patches.
>
>
> > Cc: qemu-devel@xxxxxxxxxx
> > Signed-off-by: Breno Leitao <leitao@xxxxxxxxxx>
> > ---
> > Changelog:
> >
> > V2:
> >    * Moved from creating a valid packet, by rejecting the request
> >      completely
> > V3:
> >    * Got some good feedback from and Xuan Zhuo and Heng Qi, and reworked
> >      the rejection path.
> >
> > ---
> >   drivers/net/virtio_net.c | 22 ++++++++++++++++++----
> >   1 file changed, 18 insertions(+), 4 deletions(-)
> >
> > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> > index c22d1118a133..c4a21ec51adf 100644
> > --- a/drivers/net/virtio_net.c
> > +++ b/drivers/net/virtio_net.c
> > @@ -3807,6 +3807,7 @@ static int virtnet_set_rxfh(struct net_device *dev,
> >   			    struct netlink_ext_ack *extack)
> >   {
> >   	struct virtnet_info *vi = netdev_priv(dev);
> > +	bool update = false;
> >   	int i;
> >   
> >   	if (rxfh->hfunc != ETH_RSS_HASH_NO_CHANGE &&
> > @@ -3814,13 +3815,24 @@ static int virtnet_set_rxfh(struct net_device *dev,
> >   		return -EOPNOTSUPP;
> >   
> >   	if (rxfh->indir) {
> > +		if (!vi->has_rss)
> > +			return -EOPNOTSUPP;
> > +
> >   		for (i = 0; i < vi->rss_indir_table_size; ++i)
> >   			vi->ctrl->rss.indirection_table[i] = rxfh->indir[i];
> > +		update = true;
> >   	}
> > -	if (rxfh->key)
> > +
> > +	if (rxfh->key) {
> > +		if (!vi->has_rss && !vi->has_rss_hash_report)
> > +			return -EOPNOTSUPP;
>
> What's the logic here? Is it || or &&? A comment can't hurt.

&&

Hi Breno,

You can add a comment like the following:

If either _F_HASH_REPORT or _F_RSS are negotiated, the device provides
hash calculation capabilities, that is, hash_key can be configured.

Regards,
Heng

> > +
> >   		memcpy(vi->ctrl->rss.key, rxfh->key, vi->rss_key_size);
> > +		update = true;
> > +	}
> >   
> > -	virtnet_commit_rss_command(vi);
> > +	if (update)
> > +		virtnet_commit_rss_command(vi);
> >   
> >   	return 0;
> >   }
> > @@ -4729,13 +4741,15 @@ static int virtnet_probe(struct virtio_device *vdev)
> >   	if (virtio_has_feature(vdev, VIRTIO_NET_F_HASH_REPORT))
> >   		vi->has_rss_hash_report = true;
> >   
> > -	if (virtio_has_feature(vdev, VIRTIO_NET_F_RSS))
> > +	if (virtio_has_feature(vdev, VIRTIO_NET_F_RSS)) {
> >   		vi->has_rss = true;
> >   
> > -	if (vi->has_rss || vi->has_rss_hash_report) {
> >   		vi->rss_indir_table_size =
> >   			virtio_cread16(vdev, offsetof(struct virtio_net_config,
> >   				rss_max_indirection_table_length));
> > +	}
> > +
> > +	if (vi->has_rss || vi->has_rss_hash_report) {
> >   		vi->rss_key_size =
> >   			virtio_cread8(vdev, offsetof(struct virtio_net_config, rss_max_key_size));
> >   
> > --
> > 2.43.0