> On Tue, Feb 24, 2026 at 12:28:49PM +0530, Srujana Challa wrote:
> > Replace hardcoded RSS max key size limit with NETDEV_RSS_KEY_LEN to
> > align with kernel's standard RSS key length. Add validation for RSS
> > key size against spec minimum (40 bytes) and driver maximum. When
> > validation fails, gracefully disable RSS features and continue
> > initialization rather than failing completely.
> >
> > Cc: [email protected]
> > Fixes: 3f7d9c1964fc ("virtio_net: Add hash_key_length check")
> > Signed-off-by: Srujana Challa <[email protected]>
>
> --- should come here before changelog.
>
> > 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.
> > ---
> > drivers/net/virtio_net.c | 34 ++++++++++++++++++++++++----------
> > 1 file changed, 24 insertions(+), 10 deletions(-)
> >
> > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c index
> > db88dcaefb20..eeefe8abc122 100644
> > --- a/drivers/net/virtio_net.c
> > +++ b/drivers/net/virtio_net.c
> > @@ -381,8 +381,6 @@ 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;
> > @@ -486,7 +484,7 @@ 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) == @@ -6627,6 +6625,29 @@ static int
> virtnet_validate(struct virtio_device *vdev)
> > __virtio_clear_bit(vdev, VIRTIO_NET_F_STANDBY);
> > }
> >
> > + if (virtio_has_feature(vdev, VIRTIO_NET_F_RSS) ||
> > + virtio_has_feature(vdev, VIRTIO_NET_F_HASH_REPORT)) {
> > + u8 key_sz = virtio_cread8(vdev,
> > + offsetof(struct virtio_net_config,
> > + rss_max_key_size));
> > + /* Spec requires at least 40 bytes */ #define
> > +VIRTIO_NET_RSS_MIN_KEY_SIZE 40
> > + if (key_sz < VIRTIO_NET_RSS_MIN_KEY_SIZE) {
> > + dev_warn(&vdev->dev,
> > + "rss_max_key_size=%u is less than spec
> minimum %u, disabling RSS\n",
> > + key_sz, VIRTIO_NET_RSS_MIN_KEY_SIZE);
> > + __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);
>
> you flipped the logic here and it makes no sense now.
>
> Did you test this path?
Yes, tested with Marvell's Octeon device.
>
>
> So if device is powerful and supports a very big key size then...
> we disable the feature? how does this make sense?
The intent isn’t to disable the feature on capable devices, but to ensure the
driver never advertises
support for RSS key sizes larger than what the net device can actually handle.
Even if a device reports
a very large key size, the driver is constrained by NETDEV_RSS_KEY_LEN, since
netdev_rss_key_fill() enforces:
BUG_ON(len > sizeof(netdev_rss_key));
>
>
> > + }
> > + }
> > +
> > return 0;
> > }
> >
> > @@ -6839,13 +6860,6 @@ 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;
> > - }
> > -
> > vi->rss_hash_types_supported =
> > virtio_cread32(vdev, offsetof(struct virtio_net_config,
> supported_hash_types));
> > vi->rss_hash_types_supported &=
> > --
> > 2.25.1
