On 3/26/26 3:23 PM, Srujana Challa wrote:

quoted

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: stable@vger.kernel.org
Signed-off-by: Srujana Challa <schalla@marvell.com>
---
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.

quoted

v5:
- Interpret rss_max_key_size as a maximum and clamp it to

NETDEV_RSS_KEY_LEN.

quoted

- Do not disable RSS/HASH_REPORT when device rss_max_key_size exceeds

NETDEV_RSS_KEY_LEN.

quoted

- Drop the separate patch that replaced the runtime check with

BUILD_BUG_ON.

quoted

 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,

quoted

-		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)

quoted

 	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)

quoted

 	}

 	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));

quoted

-		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",

quoted

-				vi->rss_key_size,

VIRTIO_NET_RSS_MAX_KEY_SIZE);

quoted

-			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",

quoted

+				 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