Re: [PATCH net-next,2/2] virtio_net: replace RSS key size max check with BUILD_BUG_ON

[Xuan Zhuo <xuanzhuo@linux.alibaba.com>]

On Tue, 24 Feb 2026 12:28:50 +0530, Srujana Challa <schalla@marvell.com> wrote:
> Since NETDEV_RSS_KEY_LEN was increased to 256 in net-next, use
> BUILD_BUG_ON to enforce the limit at compile time and remove the
> redundant runtime max check.
>
> Signed-off-by: Srujana Challa <schalla@marvell.com>
> ---
>  drivers/net/virtio_net.c | 8 +-------
>  1 file changed, 1 insertion(+), 7 deletions(-)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index eeefe8abc122..768ad5523dfa 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -6639,13 +6639,7 @@ static int virtnet_validate(struct virtio_device *vdev)
>  			__virtio_clear_bit(vdev, VIRTIO_NET_F_RSS);
>  			__virtio_clear_bit(vdev, VIRTIO_NET_F_HASH_REPORT);
>  		}
> -		if (key_sz > NETDEV_RSS_KEY_LEN) {
> -			dev_warn(&vdev->dev,
> -				 "rss_max_key_size=%u exceeds driver limit %u, disabling RSS\n",
> -				 key_sz, NETDEV_RSS_KEY_LEN);
> -			__virtio_clear_bit(vdev, VIRTIO_NET_F_RSS);
> -			__virtio_clear_bit(vdev, VIRTIO_NET_F_HASH_REPORT);
> -		}
> +		BUILD_BUG_ON(type_max(key_sz) >= NETDEV_RSS_KEY_LEN);

Do we really need this check?

If I understand correctly, the intention is to cap key_sz at 256. However, since
key_sz is of type u8, its maximum value is inherently 255, making this check
redundant. This is not only limited by this kernel code, the virtio-net spec
defines this.

Moreover, if NETDEV_RSS_KEY_LEN is ever reduced to a value smaller than 256 in
the future, this check would no longer enforce the intended limit correctly.


Moreover, you should add a cover letter.

Thanks.





>  	}
>
>  	return 0;
> --
> 2.25.1
>