netdev - Re: [PATCH v16 bpf-next 09/20] bpf: introduce BPF_F_XDP_MB flag in prog

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Message-ID: <87lf2uz34s.fsf@toke.dk>
Date:   Fri, 15 Oct 2021 18:03:47 +0200
From:   Toke Høiland-Jørgensen <toke@...hat.com>
To:     Lorenzo Bianconi <lorenzo@...nel.org>
Cc:     bpf@...r.kernel.org, netdev@...r.kernel.org,
        lorenzo.bianconi@...hat.com, davem@...emloft.net, kuba@...nel.org,
        ast@...nel.org, daniel@...earbox.net, shayagr@...zon.com,
        john.fastabend@...il.com, dsahern@...nel.org, brouer@...hat.com,
        echaudro@...hat.com, jasowang@...hat.com,
        alexander.duyck@...il.com, saeed@...nel.org,
        maciej.fijalkowski@...el.com, magnus.karlsson@...el.com,
        tirthendu.sarkar@...el.com
Subject: Re: [PATCH v16 bpf-next 09/20] bpf: introduce BPF_F_XDP_MB flag in
 prog_flags loading the ebpf program

Lorenzo Bianconi <lorenzo@...nel.org> writes:

>> Lorenzo Bianconi <lorenzo@...nel.org> writes:
>> 
>> > Introduce BPF_F_XDP_MB and the related field in bpf_prog_aux in order to
>> > notify the driver the loaded program support xdp multi-buffer.
>> 
>> We should also add some restrictions in the BPF core. In particular,
>> tail call, cpumap and devmap maps should not be able to mix multi-buf
>> and non-multibuf programs.
>
> ack. How can we detect if a cpumap or a devmap is running in XDP multi-buff
> mode in order to reject loading the legacy XDP program?

I was hoping we could copy the same mechanism that tail call maps to
ensure that callers and callees are the same type. And amend that to
also consider the xdp_mb flag while we're at it :)

> Should we just discard the XDP multi-buff in this case?

If I'm right in the above, we won't have to because the verifier can
ensure that the program types match...

-Toke