Re: [PATCH bpf-next v5 8/8] selftests: net: add test for XDP_PASS skb checksum invalidation

[Jakub Kicinski <kuba@kernel.org>]

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).