On Thu, Mar 26, 2026 at 07:53:44PM +0530, Srujana Challa wrote:
> 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: [email protected]
> Signed-off-by: Srujana Challa <[email protected]>
Acked-by: Michael S. Tsirkin <[email protected]>
> ---
> v3:
> - Moved RSS key validation checks to virtnet_validate.
> - Add fixes: tag and CC -stable
> v4:
> - Use NETDEV_RSS_KEY_LEN instead of type_max for the maximum rss key size.
> v5:
> - Interpret rss_max_key_size as a maximum and clamp it to NETDEV_RSS_KEY_LEN.
> - Do not disable RSS/HASH_REPORT when device rss_max_key_size exceeds
> NETDEV_RSS_KEY_LEN.
> - Drop the separate patch that replaced the runtime check with BUILD_BUG_ON.
>
> drivers/net/virtio_net.c | 20 +++++++++-----------
> 1 file changed, 9 insertions(+), 11 deletions(-)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 022f60728721..b241c8dbb4e1 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -373,8 +373,6 @@ struct receive_queue {
> struct xdp_buff **xsk_buffs;
> };
>
> -#define VIRTIO_NET_RSS_MAX_KEY_SIZE 40
> -
> /* Control VQ buffers: protected by the rtnl lock */
> struct control_buf {
> struct virtio_net_ctrl_hdr hdr;
> @@ -478,7 +476,7 @@ struct virtnet_info {
>
> /* Must be last as it ends in a flexible-array member. */
> TRAILING_OVERLAP(struct virtio_net_rss_config_trailer, rss_trailer,
> hash_key_data,
> - u8 rss_hash_key_data[VIRTIO_NET_RSS_MAX_KEY_SIZE];
> + u8 rss_hash_key_data[NETDEV_RSS_KEY_LEN];
> );
> };
> static_assert(offsetof(struct virtnet_info, rss_trailer.hash_key_data) ==
> @@ -6717,6 +6715,7 @@ 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;
> @@ -6851,14 +6850,13 @@ 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, NETDEV_RSS_KEY_LEN);
> + 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));
> --
> 2.25.1
