netdev - Re: [PATCH RFC bpf-next v2 0/5] Add the the capability to load HW RX checsum in eBPF programs

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Message-ID: <87tt0q3ik9.fsf@cloudflare.com>
Date: Thu, 25 Sep 2025 12:58:14 +0200
From: Jakub Sitnicki <jakub@...udflare.com>
To: Lorenzo Bianconi <lorenzo@...nel.org>
Cc: Donald Hunter <donald.hunter@...il.com>,  Jakub Kicinski
 <kuba@...nel.org>,  "David S. Miller" <davem@...emloft.net>,  Eric Dumazet
 <edumazet@...gle.com>,  Paolo Abeni <pabeni@...hat.com>,  Simon Horman
 <horms@...nel.org>,  Alexei Starovoitov <ast@...nel.org>,  Daniel Borkmann
 <daniel@...earbox.net>,  Jesper Dangaard Brouer <hawk@...nel.org>,  John
 Fastabend <john.fastabend@...il.com>,  Stanislav Fomichev
 <sdf@...ichev.me>,  Andrew Lunn <andrew+netdev@...n.ch>,  Tony Nguyen
 <anthony.l.nguyen@...el.com>,  Przemek Kitszel
 <przemyslaw.kitszel@...el.com>,  Alexander Lobakin
 <aleksander.lobakin@...el.com>,  Andrii Nakryiko <andrii@...nel.org>,
  Martin KaFai Lau <martin.lau@...ux.dev>,  Eduard Zingerman
 <eddyz87@...il.com>,  Song Liu <song@...nel.org>,  Yonghong Song
 <yonghong.song@...ux.dev>,  KP Singh <kpsingh@...nel.org>,  Hao Luo
 <haoluo@...gle.com>,  Jiri Olsa <jolsa@...nel.org>,  Shuah Khan
 <shuah@...nel.org>,  Maciej Fijalkowski <maciej.fijalkowski@...el.com>,
  netdev@...r.kernel.org,  bpf@...r.kernel.org,
  intel-wired-lan@...ts.osuosl.org,  linux-kselftest@...r.kernel.org
Subject: Re: [PATCH RFC bpf-next v2 0/5] Add the the capability to load HW
 RX checsum in eBPF programs

On Thu, Sep 25, 2025 at 12:39 PM +02, Lorenzo Bianconi wrote:
>> On Thu, Sep 25, 2025 at 11:30 AM +02, Lorenzo Bianconi wrote:
>> > Introduce bpf_xdp_metadata_rx_checksum() kfunc in order to load the HW
>> > RX cheksum results in the eBPF program binded to the NIC.
>> > Implement xmo_rx_checksum callback for veth and ice drivers.
>> 
>> What are going to do with HW RX checksum once XDP prog can access it?
>
> I guess there are multiple use-cases for bpf_xdp_metadata_rx_checksum()
> kfunc. The first the I have in mind is when packets are received by an af_xdp
> application. In this case I think we currently do not have any way to check if
> the packet checksum is correct, right?
> I think Jesper has other use-cases in mind, I will let him comment
> here.

Can you share more details on what the AF_XDP application would that
info?

Regarding the use cases that Jesper is trying to unlock, as things stand
we don't have a way, or an agreement on how to inject/propagate even the
already existing NIC hints back into the network stack.

Hence my question - why do we want to expose another NIC hint to XDP
that we can't consume in any useful way yet?

Shouldn't we first figure out how we're planning to re-inject that info
into the stack?