Re: [PATCH] virtio-net: Zero max_tx_vq field for VIRTIO_NET_CTRL_MQ_HASH_CONFIG case

[Eugenio Perez Martin]

On Thu, Aug 10, 2023 at 5:16 AM Hawkins Jiawei <yin31149@xxxxxxxxx> wrote:
>
> Kernel uses `struct virtio_net_ctrl_rss` to save command-specific-data
> for both the VIRTIO_NET_CTRL_MQ_HASH_CONFIG and
> VIRTIO_NET_CTRL_MQ_RSS_CONFIG commands.
>
> According to the VirtIO standard, "Field reserved MUST contain zeroes.
> It is defined to make the structure to match the layout of
> virtio_net_rss_config structure, defined in 5.1.6.5.7.".
>
> Yet for the VIRTIO_NET_CTRL_MQ_HASH_CONFIG command case, the `max_tx_vq`
> field in struct virtio_net_ctrl_rss, which corresponds to the
> `reserved` field in struct virtio_net_hash_config, is not zeroed,
> thereby violating the VirtIO standard.
>
> This patch solves this problem by zeroing this field in
> virtnet_init_default_rss().
>
> Signed-off-by: Hawkins Jiawei <yin31149@xxxxxxxxx>

Acked-by: Eugenio Pérez <eperezma@xxxxxxxxxx>

> ---
>
> TestStep
> ========
> 1. Boot QEMU with one virtio-net-pci net device with `mq` and `hash`
> feature on, command line like:
>       -netdev tap,vhost=off,...
>       -device virtio-net-pci,mq=on,hash=on,...
>
> 2. Trigger VIRTIO_NET_CTRL_MQ_HASH_CONFIG command in guest, command
> line like:
>         ethtool -K eth0 rxhash on
>
> Without this patch, in virtnet_commit_rss_command(), we can see the
> `max_tx_vq` field is 1 in gdb like below:
>
>         pwndbg> p vi->ctrl->rss
>         $1 = {
>           hash_types = 63,
>           indirection_table_mask = 0,
>           unclassified_queue = 0,
>           indirection_table = {0 <repeats 128 times>},
>           max_tx_vq = 1,
>           hash_key_length = 40 '(',
>           ...
>         }
>
> With this patch, in virtnet_commit_rss_command(), we can see the
> `max_tx_vq` field is 0 in gdb like below:
>
>         pwndbg> p vi->ctrl->rss
>         $1 = {
>           hash_types = 63,
>           indirection_table_mask = 0,
>           unclassified_queue = 0,
>           indirection_table = {0 <repeats 128 times>},
>           max_tx_vq = 0,
>           hash_key_length = 40 '(',
>           ...
>         }
>
>  drivers/net/virtio_net.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 1270c8d23463..8db38634ae82 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -2761,7 +2761,7 @@ static void virtnet_init_default_rss(struct virtnet_info *vi)
>                 vi->ctrl->rss.indirection_table[i] = indir_val;
>         }
>
> -       vi->ctrl->rss.max_tx_vq = vi->curr_queue_pairs;
> +       vi->ctrl->rss.max_tx_vq = vi->has_rss ? vi->curr_queue_pairs : 0;
>         vi->ctrl->rss.hash_key_length = vi->rss_key_size;
>
>         netdev_rss_key_fill(vi->ctrl->rss.key, vi->rss_key_size);
> --
> 2.34.1
>