> On Thu, Jan 22, 2026 at 02:45:27PM +0530, Srujana Challa wrote:
> > Increase VIRTIO_NET_RSS_MAX_KEY_SIZE from 40 to 52 bytes to align with
> > the kernel's standard RSS key length defined by NETDEV_RSS_KEY_LEN.
> >
> > The virtio specification requires devices to support at least 40 bytes
> > for the RSS key size.
>
> Indeed:
> The device MUST set \field{rss_max_key_size} to at least 40, if it
> offers
> VIRTIO_NET_F_RSS or VIRTIO_NET_F_HASH_REPORT.
>
>
>
> > However, devices may support larger key sizes up to 52 bytes (as
> > reported by the device's rss_max_key_size config field). This change
> > allows such devices to work properly.
> > Previously, devices reporting rss_max_key_size > 40 would fail with an
> > error during initialization.
>
> This one, yes?
>
> 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;
> }
>
>
> Hmm but why do we do it like this? I suspect we just got confused with the
> spec: > vs <.
I believe the check was added to prevent out-of-bounds errors when
accessing the hash key buffer.
>
>
> Can't we just do:
> min(vi->rss_key_size, VIRTIO_NET_RSS_MAX_KEY_SIZE)
Our device requires hash_key_length to exactly match rss_max_key_size
for symmetric bidirectional flow hashing. When rss_max_key_size >
VIRTIO_NET_RSS_MAX_KEY_SIZE, clamping isn't possible. Should we
disable RSS instead of failing initialization?
Thanks.
>
>
> If yes I'd like that fix in addition to the increase.
>
>
>
> If we are validating rss_key_size against 40, I think we should clear the
> feature
> rather than failing init completely.
>
>
>
>
>
>
> > The driver already handles variable key sizes dynamically through
> > vi->rss_key_size, so increasing the maximum limit is safe and
> > maintains backward compatibility with devices that support smaller key
> > sizes.
> >
> > Signed-off-by: Srujana Challa <[email protected]>
> > ---
> > drivers/net/virtio_net.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c index
> > db88dcaefb20..5f06cbc058d7 100644
> > --- a/drivers/net/virtio_net.c
> > +++ b/drivers/net/virtio_net.c
> > @@ -381,7 +381,7 @@ struct receive_queue {
> > struct xdp_buff **xsk_buffs;
> > };
> >
> > -#define VIRTIO_NET_RSS_MAX_KEY_SIZE 40
> > +#define VIRTIO_NET_RSS_MAX_KEY_SIZE 52
> >
> > /* Control VQ buffers: protected by the rtnl lock */ struct
> > control_buf {
> > --
> > 2.25.1
