> > -----Original Message-----
> > From: Michael S. Tsirkin <[email protected]>
> > Sent: Wednesday, February 25, 2026 6:07 PM
> > To: Srujana Challa <[email protected]>
> > Cc: [email protected]; [email protected];
> > [email protected]; [email protected]; [email protected];
> > [email protected]; [email protected]; [email protected];
> > [email protected]; Nithin Kumar Dabilpuram <[email protected]>;
> > Shiva Shankar Kommula <[email protected]>; [email protected]
> > Subject: Re: [EXTERNAL] Re: [PATCH net,v4,1/2] virtio_net: Improve RSS
> > key size validation and use NETDEV_RSS_KEY_LEN
> >
> > On Wed, Feb 25, 2026 at 12: 34: 28PM +0000, Srujana Challa wrote: > >
> > > > 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 > ZjQcmQRYFpfptBannerStart Prioritize security for
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> > On Wed, Feb 25, 2026 at 12:34:28PM +0000, Srujana Challa wrote:
> > > > > > 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));
> > > >
> > > > so cap it to NETDEV_RSS_KEY_LEN. Why is that a reason to clear the
> > feature?
> > > Our device mandates that hash_key_length must be identical to
> > > rss_max_key_size to guarantee symmetric bidirectional flow hashing.
> > > If rss_max_key_size is larger than VIRTIO_NET_RSS_MAX_KEY_SIZE,
> > > clamping
> > the value is not feasible.
> >
> > I don't know what to tell you. rss_max_key_size is just the max device
> > supports. driver should be free to use a smaller size.
> My understanding is that this patch prevents the probe from failing by
> disabling the feature instead.
> Given the current implementation, the driver becomes unusable when this
> condition is hit.
I understand that the driver is allowed to use a smaller RSS key than the
device’s advertised rss_max_key_size.
But, our hardware does not behave correctly in that configuration. For
symmetric bidirectional hashing,
the device requires that the hash_key_length match rss_max_key_size exactly.
If the driver uses a smaller key, the hardware produces inconsistent hash
values for forward vs reverse flows.
Because of this device requirement, we cannot cap the key to NETDEV_RSS_KEY_LEN
when the device advertises
a larger rss_max_key_size.
> >
> >
> > > >
> > > > > >
> > > > > >
> > > > > > > + }
> > > > > > > + }
> > > > > > > +
> > > > > > > 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
> > > > >
> > >
