Re: [PATCH 6.1.y] virtio_net: clamp rss_max_key_size to NETDEV_RSS_KEY_LEN

["Michael S. Tsirkin" <mst@redhat.com>]

On Wed, Apr 08, 2026 at 09:43:51AM -0400, Sasha Levin wrote:
> From: Srujana Challa <schalla@marvell.com>
> 
> [ Upstream commit b4e5f04c58a29c499faa85d12952ca9a4faf1cb9 ]
> 
> rss_max_key_size in the virtio spec is the maximum key size supported by
> the device, not a mandatory size the driver must use. Also the value 40
> is a spec minimum, not a spec maximum.
> 
> The current code rejects RSS and can fail probe when the device reports a
> larger rss_max_key_size than the driver buffer limit. Instead, clamp the
> effective key length to min(device rss_max_key_size, NETDEV_RSS_KEY_LEN)
> and keep RSS enabled.
> 
> This keeps probe working on devices that advertise larger maximum key sizes
> while respecting the netdev RSS key buffer size limit.
> 
> Fixes: 3f7d9c1964fc ("virtio_net: Add hash_key_length check")
> Cc: stable@vger.kernel.org
> Signed-off-by: Srujana Challa <schalla@marvell.com>
> Acked-by: Michael S. Tsirkin <mst@redhat.com>
> Link: https://patch.msgid.link/20260326142344.1171317-1-schalla@marvell.com
> Signed-off-by: Jakub Kicinski <kuba@kernel.org>
> [ changed clamp target from NETDEV_RSS_KEY_LEN to VIRTIO_NET_RSS_MAX_KEY_SIZE ]

Does this not make the subject and the commit log misleading?

> Signed-off-by: Sasha Levin <sashal@kernel.org>
> ---
>  drivers/net/virtio_net.c | 16 ++++++++--------
>  1 file changed, 8 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 9ee3465082c5a..0fcd662d15d51 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -3796,6 +3796,7 @@ static int virtnet_probe(struct virtio_device *vdev)
>  	struct virtnet_info *vi;
>  	u16 max_queue_pairs;
>  	int mtu = 0;
> +	u16 key_sz;
>  
>  	/* Find if host supports multiqueue/rss virtio_net device */
>  	max_queue_pairs = 1;
> @@ -3915,14 +3916,13 @@ static int virtnet_probe(struct virtio_device *vdev)
>  	}
>  
>  	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));
> -		if (vi->rss_key_size > VIRTIO_NET_RSS_MAX_KEY_SIZE) {
> -			dev_err(&vdev->dev, "rss_max_key_size=%u exceeds the limit %u.\n",
> -				vi->rss_key_size, VIRTIO_NET_RSS_MAX_KEY_SIZE);
> -			err = -EINVAL;
> -			goto free;
> -		}
> +		key_sz = virtio_cread8(vdev, offsetof(struct virtio_net_config, rss_max_key_size));
> +
> +		vi->rss_key_size = min_t(u16, key_sz, VIRTIO_NET_RSS_MAX_KEY_SIZE);
> +		if (key_sz > vi->rss_key_size)
> +			dev_warn(&vdev->dev,
> +				 "rss_max_key_size=%u exceeds driver limit %u, clamping\n",
> +				 key_sz, vi->rss_key_size);
>  
>  		vi->rss_hash_types_supported =
>  		    virtio_cread32(vdev, offsetof(struct virtio_net_config, supported_hash_types));
> -- 
> 2.53.0