netdev - Re: [xdp-hints] [PATCH bpf-next v4 05/15] bpf: XDP metadata RX kfuncs

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Message-ID: <CAKH8qBtcmELXh9pHedkmEDTkPJRVNNs3ES218+npC3oYcNpN=Q@mail.gmail.com>
Date:   Wed, 14 Dec 2022 10:43:12 -0800
From:   Stanislav Fomichev <sdf@...gle.com>
To:     Toke Høiland-Jørgensen <toke@...hat.com>
Cc:     bpf@...r.kernel.org, ast@...nel.org, daniel@...earbox.net,
        andrii@...nel.org, martin.lau@...ux.dev, song@...nel.org,
        yhs@...com, john.fastabend@...il.com, kpsingh@...nel.org,
        haoluo@...gle.com, jolsa@...nel.org,
        David Ahern <dsahern@...il.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Willem de Bruijn <willemb@...gle.com>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        Anatoly Burakov <anatoly.burakov@...el.com>,
        Alexander Lobakin <alexandr.lobakin@...el.com>,
        Magnus Karlsson <magnus.karlsson@...il.com>,
        Maryam Tahhan <mtahhan@...hat.com>, xdp-hints@...-project.net,
        netdev@...r.kernel.org
Subject: Re: [xdp-hints] [PATCH bpf-next v4 05/15] bpf: XDP metadata RX kfuncs

On Wed, Dec 14, 2022 at 2:54 AM Toke Høiland-Jørgensen <toke@...hat.com> wrote:
>
> Stanislav Fomichev <sdf@...gle.com> writes:
>
> [..]
>
> > diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
> > index d434a994ee04..c3e501e3e39c 100644
> > --- a/kernel/bpf/core.c
> > +++ b/kernel/bpf/core.c
> > @@ -2097,6 +2097,13 @@ bool bpf_prog_map_compatible(struct bpf_map *map,
> >       if (fp->kprobe_override)
> >               return false;
> >
> > +     /* When tail-calling from a non-dev-bound program to a dev-bound one,
> > +      * XDP metadata helpers should be disabled. Until it's implemented,
> > +      * prohibit adding dev-bound programs to tail-call maps.
> > +      */
> > +     if (bpf_prog_is_dev_bound(fp->aux))
> > +             return false;
> > +
>
> nit: the comment is slightly inaccurate as the program running in a
> devmap/cpumap has nothing to do with tail calls. maybe replace it with:
>
> "XDP programs inserted into maps are not guaranteed to run on a
> particular netdev (and can run outside driver context entirely in the
> case of devmap and cpumap). Until device checks are implemented,
> prohibit adding dev-bound programs to program maps."

SG.

> Also, there needs to be a check in bpf_prog_test_run_xdp() to reject
> dev-bound programs there as well...

Ah, totally forgot about this part, thanks for reminding!

> -Toke
>