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Date: Tue, 21 Jul 2026 08:27:28 -0700
From: Jakub Kicinski <kuba@kernel.org>
To: Stanislav Fomichev <sdf.kernel@gmail.com>
Cc: Lorenzo Bianconi <lorenzo@kernel.org>, Donald Hunter
 <donald.hunter@gmail.com>, "David S. Miller" <davem@davemloft.net>, Eric
 Dumazet <edumazet@google.com>, Paolo Abeni <pabeni@redhat.com>, Simon
 Horman <horms@kernel.org>, Alexei Starovoitov <ast@kernel.org>, Daniel
 Borkmann <daniel@iogearbox.net>, Jesper Dangaard Brouer <hawk@kernel.org>,
 John Fastabend <john.fastabend@gmail.com>, Stanislav Fomichev
 <sdf@fomichev.me>, Andrew Lunn <andrew+netdev@lunn.ch>, Tony Nguyen
 <anthony.l.nguyen@intel.com>, Przemek Kitszel
 <przemyslaw.kitszel@intel.com>, Alexander Lobakin
 <aleksander.lobakin@intel.com>, Andrii Nakryiko <andrii@kernel.org>, Martin
 KaFai Lau <martin.lau@linux.dev>, Eduard Zingerman <eddyz87@gmail.com>,
 Song Liu <song@kernel.org>, Yonghong Song <yonghong.song@linux.dev>, KP
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 <jolsa@kernel.org>, Shuah Khan <shuah@kernel.org>, Maciej Fijalkowski
 <maciej.fijalkowski@intel.com>, Jonathan Corbet <corbet@lwn.net>, Shuah
 Khan <skhan@linuxfoundation.org>, Kumar Kartikeya Dwivedi
 <memxor@gmail.com>, Emil Tsalapatis <emil@etsalapatis.com>, Vladimir Vdovin
 <deliran@verdict.gg>, Jakub Sitnicki <jakub@cloudflare.com>,
 netdev@vger.kernel.org, bpf@vger.kernel.org,
 intel-wired-lan@lists.osuosl.org, linux-kselftest@vger.kernel.org,
 linux-doc@vger.kernel.org
Subject: Re: [PATCH bpf-next v5 8/8] selftests: net: add test for XDP_PASS
 skb checksum invalidation
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On Mon, 20 Jul 2026 12:32:55 -0700 Stanislav Fomichev wrote:
> > > (although for gve I might be wrong, there is also gve_rx_skb_csum that only
> > > does UNNECESSARY).
> > > 
> > > I'd wait for Jakub to chime in, but it feels like we should just document
> > > what we currently do as a recommended approach: for the drivers
> > > that support COMPLETE, do not report it when the bpf program is attached.
> > > Both NONE and UNNECESSARY are ok.  
> > 
> > I am not completely sure the UNNECESSARY case is different from the COMPLETE
> > one. What are we supposed to do if the driver reports UNNECESSARY and the ebpf
> > program modifies some fields covered by the rx-checksum?  
> 
> For unnecessary, I think the safe expectation is that the bpf program
> will update the value of the checksum in the packet if it touches the data?

Documenting as expected behavior which no driver currently follows 
is a bit silly. I thought the ask was to sketch out the plan of
explicitly updating/invalidating the checksum even if we don't
implement it today?

> > > Also, did you run this test on real HW? NIPA now has HW tests, maybe it
> > > makes sense to route this series via net-next to get the real coverage?  
> > 
> > What about splitting this series and have two different series:
> > - bpf-next: add xdp rx kfunc and related selftest
> > - net-next: add kselftest for the driver expected behaviour.
> > 
> > What do you think?  
> 
> I'd post everything to net-next to get the HW coverage. Once you get all
> the acks we can ask the maintainers' guidance.

+1, and please add proper tests for the real drivers exercising the
kfunc with traffic (would be good to try to send a non-TCP/UDP frame
to try to cajole the driver into using COMPLETE).