On Wed, 25 Feb 2026 04:33:57 -0500, "Michael S. Tsirkin" [off-list ref] wrote:

On Wed, Feb 25, 2026 at 05:30:33PM +0800, Xuan Zhuo wrote:

quoted

On Wed, 25 Feb 2026 04:24:14 -0500, "Michael S. Tsirkin" [off-list ref] wrote:

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On Wed, Feb 25, 2026 at 05:11:42PM +0800, Xuan Zhuo wrote:

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On Tue, 24 Feb 2026 12:28:50 +0530, Srujana Challa [off-list ref] wrote:

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Since NETDEV_RSS_KEY_LEN was increased to 256 in net-next, use
BUILD_BUG_ON to enforce the limit at compile time and remove the
redundant runtime max check.

Signed-off-by: Srujana Challa <schalla@marvell.com>
---
 drivers/net/virtio_net.c | 8 +-------
 1 file changed, 1 insertion(+), 7 deletions(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index eeefe8abc122..768ad5523dfa 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c

@@ -6639,13 +6639,7 @@ static int virtnet_validate(struct virtio_device *vdev)
 			__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);
-		}
+		BUILD_BUG_ON(type_max(key_sz) >= NETDEV_RSS_KEY_LEN);

Do we really need this check?

If I understand correctly, the intention is to cap key_sz at 256. However, since
key_sz is of type u8, its maximum value is inherently 255, making this check
redundant. This is not only limited by this kernel code, the virtio-net spec
defines this.

That's why it's BUILD_BUG_ON. It checks it has the right type.

We never *need* BUILD_BUG_ON by definition, what this does is
document the assumption.

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Moreover, if NETDEV_RSS_KEY_LEN is ever reduced to a value smaller than 256 in
the future, this check would no longer enforce the intended limit correctly.

then it would fail build.

So, does this mean we don't need to account for the case where
NETDEV_RSS_KEY_LEN is 128, but the key_sz reported by the device is 64?

Thanks.

yes.

Why?

If NETDEV_RSS_KEY_LEN is 128 but the device reports a key_sz of 64, does this
violate the spec?

the code makes assumptions but it documents them and not
just documents them, build will fail if they are violated.

About this, I am ok.

Thanks.

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Moreover, you should add a cover letter.

Thanks.

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 	}

 	return 0;
--
2.25.1