Subject: Re: [PATCH v2 net-next] virtio_net: Improve RSS key size validation and use NETDEV_RSS_KEY_LEN

From: "Michael S. Tsirkin" <[email-masked]>
Date: Sat, 7 Feb 2026 04:56:13 -0500

On Fri, Feb 06, 2026 at 07:13:08PM -0800, Jakub Kicinski wrote:
> On Fri, 6 Feb 2026 17:31:54 +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.
> 
> Hm, FWIW clang says:
> 
> drivers/net/virtio_net.c:6841:31: warning: result of comparison of constant 256 with expression of type 'u8' (aka 'unsigned char') is always false [-Wtautological-constant-out-of-range-compare]
>  6841 |                 } else if (vi->rss_key_size > VIRTIO_NET_RSS_MAX_KEY_SIZE) {
>       |                            ~~~~~~~~~~~~~~~~ ^ ~~~~~~~~~~~~~~~~~~~~~~~~~~~
> 
> Which is kinda annoying because the value was increased in net-next.
> If Machael wants this backported then we need to keep the check
> and follow up in net-next? We could try to cast the u32 away but
> that feels dirty..

I'd say yes. the warning is harmless.
so
patch 1 - this code
patch 2 - replace with BUILD_BUG_ON

but i ask then whether this code was actually tested against net-next.

-- 
MST