virtio-net: Zero max_tx_vq field for VIRTIO_NET_CTRL_MQ_HASH_CONFIG case

commit 2c507ce upstream.

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().

Cc: Andrew Melnychenko <andrew@daynix.com>
Cc: stable@vger.kernel.org
Fixes: c7114b1 ("drivers/net/virtio_net: Added basic RSS support.")
Signed-off-by: Hawkins Jiawei <yin31149@gmail.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Acked-by: Eugenio Pérez <eperezma@redhat.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Message-Id: <20230810110405.25558-1-yin31149@gmail.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/net/virtio_net.c

@@ -2504,7 +2504,7 @@ 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);