Re: [PATCH net v2 2/2] virtio_net: Do not send RSS key if it is not supported

[Heng Qi]

在 2024/3/26 下午11:19, Breno Leitao 写道:
> 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
> Cc: qemu-devel@xxxxxxxxxx
> Signed-off-by: Breno Leitao <leitao@xxxxxxxxxx>
> ---
>   drivers/net/virtio_net.c | 3 +++
>   1 file changed, 3 insertions(+)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index c640fdf28fc5..e6b0eaf08ac2 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -3809,6 +3809,9 @@ static int virtnet_set_rxfh(struct net_device *dev,
>   	struct virtnet_info *vi = netdev_priv(dev);
>   	int i;
>   
> +	if (!vi->has_rss && !vi->has_rss_hash_report)
> +		return -EOPNOTSUPP;
> +

Why not make the second patch as the first, this seems to work better.
Or squash them into one patch.

Apart from these and Xuan's comments.

For series:

        Reviewed-by: Heng Qi <hengqi@xxxxxxxxxxxxxxxxx>

Regards,
Heng

>   	if (rxfh->hfunc != ETH_RSS_HASH_NO_CHANGE &&
>   	    rxfh->hfunc != ETH_RSS_HASH_TOP)
>   		return -EOPNOTSUPP;