linux-kernel - Re: [RFC PATCH v2 1/7] bpf: Introduce BPF_PROG_TYPE_VNET

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Message-ID: <CACGkMEs22078F7rSLEz6eQabkZZ=kujSONUNMThZz5Gp=YiidQ@mail.gmail.com>
Date:   Tue, 17 Oct 2023 10:38:00 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc:     Akihiko Odaki <akihiko.odaki@...nix.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <martin.lau@...ux.dev>,
        Song Liu <song@...nel.org>,
        Yonghong Song <yonghong.song@...ux.dev>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>,
        Stanislav Fomichev <sdf@...gle.com>,
        Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>,
        Jonathan Corbet <corbet@....net>,
        Willem de Bruijn <willemdebruijn.kernel@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Xuan Zhuo <xuanzhuo@...ux.alibaba.com>,
        Mykola Lysenko <mykolal@...com>, Shuah Khan <shuah@...nel.org>,
        bpf <bpf@...r.kernel.org>,
        "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Network Development <netdev@...r.kernel.org>,
        kvm@...r.kernel.org, virtualization@...ts.linux-foundation.org,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@...r.kernel.org>,
        Yuri Benditovich <yuri.benditovich@...nix.com>,
        Andrew Melnychenko <andrew@...nix.com>
Subject: Re: [RFC PATCH v2 1/7] bpf: Introduce BPF_PROG_TYPE_VNET_HASH

On Tue, Oct 17, 2023 at 7:53 AM Alexei Starovoitov
<alexei.starovoitov@...il.com> wrote:
>
> On Sun, Oct 15, 2023 at 10:10 AM Akihiko Odaki <akihiko.odaki@...nix.com> wrote:
> >
> > On 2023/10/16 1:07, Alexei Starovoitov wrote:
> > > On Sun, Oct 15, 2023 at 7:17 AM Akihiko Odaki <akihiko.odaki@...nix.com> wrote:
> > >>
> > >> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> > >> index 0448700890f7..298634556fab 100644
> > >> --- a/include/uapi/linux/bpf.h
> > >> +++ b/include/uapi/linux/bpf.h
> > >> @@ -988,6 +988,7 @@ enum bpf_prog_type {
> > >>          BPF_PROG_TYPE_SK_LOOKUP,
> > >>          BPF_PROG_TYPE_SYSCALL, /* a program that can execute syscalls */
> > >>          BPF_PROG_TYPE_NETFILTER,
> > >> +       BPF_PROG_TYPE_VNET_HASH,
> > >
> > > Sorry, we do not add new stable program types anymore.
> > >
> > >> @@ -6111,6 +6112,10 @@ struct __sk_buff {
> > >>          __u8  tstamp_type;
> > >>          __u32 :24;              /* Padding, future use. */
> > >>          __u64 hwtstamp;
> > >> +
> > >> +       __u32 vnet_hash_value;
> > >> +       __u16 vnet_hash_report;
> > >> +       __u16 vnet_rss_queue;
> > >>   };
> > >
> > > we also do not add anything to uapi __sk_buff.
> > >
> > >> +const struct bpf_verifier_ops vnet_hash_verifier_ops = {
> > >> +       .get_func_proto         = sk_filter_func_proto,
> > >> +       .is_valid_access        = sk_filter_is_valid_access,
> > >> +       .convert_ctx_access     = bpf_convert_ctx_access,
> > >> +       .gen_ld_abs             = bpf_gen_ld_abs,
> > >> +};
> > >
> > > and we don't do ctx rewrites like this either.
> > >
> > > Please see how hid-bpf and cgroup rstat are hooking up bpf
> > > in _unstable_ way.
> >
> > Can you describe what "stable" and "unstable" mean here? I'm new to BPF
> > and I'm worried if it may mean the interface stability.
> >
> > Let me describe the context. QEMU bundles an eBPF program that is used
> > for the "eBPF steering program" feature of tun. Now I'm proposing to
> > extend the feature to allow to return some values to the userspace and
> > vhost_net. As such, the extension needs to be done in a way that ensures
> > interface stability.
>
> bpf is not an option then.
> we do not add stable bpf program types or hooks any more.

Does this mean eBPF could not be used for any new use cases other than
the existing ones?

> If a kernel subsystem wants to use bpf it needs to accept the fact
> that such bpf extensibility will be unstable and subsystem maintainers
> can decide to remove such bpf support in the future.

I don't see how it is different from the existing ones.

Thanks

>