> On 3/26/26 3:23 PM, 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]>
> > ---
> > 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);
>
> NETDEV_RSS_KEY_LEN is 256 and virtio_cread8() returns a u8. The check is
> not needed, and the warning will never be printed. I think that the
> BUILD_BUG_ON() you used in v4 would be better than the above chunk.
>
Thank you for the feedback. In net-next, NETDEV_RSS_KEY_LEN is 256. This fix is
also intended for stable kernels, where NETDEV_RSS_KEY_LEN is 52, and
I added the message to make clamping visible in that case.
I will remove the check and send the next version.
> /P
