Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::3:5 as permitted sender) client-ip=2620:137:e000::3:5;
MIME-Version: 1.0
References: <20231015141644.260646-1-akihiko.odaki@daynix.com>
 <20231015141644.260646-2-akihiko.odaki@daynix.com> <CAADnVQLfUDmgYng8Cw1hiZOMfWNWLjbn7ZGc4yOEz-XmeFEz5Q@mail.gmail.com>
 <2594bb24-74dc-4785-b46d-e1bffcc3e7ed@daynix.com> <CAADnVQ+J+bOtvEfdvgUse_Rr07rM5KOZ5DtAmHDgRmi70W68+g@mail.gmail.com>
 <CACGkMEs22078F7rSLEz6eQabkZZ=kujSONUNMThZz5Gp=YiidQ@mail.gmail.com>
In-Reply-To: <CACGkMEs22078F7rSLEz6eQabkZZ=kujSONUNMThZz5Gp=YiidQ@mail.gmail.com>
From:   Alexei Starovoitov <alexei.starovoitov@gmail.com>
Date:   Tue, 17 Oct 2023 12:03:48 -0700
Message-ID: <CAADnVQLt8NWvP8qGWMPx=12PwWWE69P7aS2dbm=khAJkCnJEoQ@mail.gmail.com>
Subject: Re: [RFC PATCH v2 1/7] bpf: Introduce BPF_PROG_TYPE_VNET_HASH
To:     Jason Wang <jasowang@redhat.com>
Cc:     Akihiko Odaki <akihiko.odaki@daynix.com>,
        Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Andrii Nakryiko <andrii@kernel.org>,
        Martin KaFai Lau <martin.lau@linux.dev>,
        Song Liu <song@kernel.org>,
        Yonghong Song <yonghong.song@linux.dev>,
        John Fastabend <john.fastabend@gmail.com>,
        KP Singh <kpsingh@kernel.org>,
        Stanislav Fomichev <sdf@google.com>,
        Hao Luo <haoluo@google.com>, Jiri Olsa <jolsa@kernel.org>,
        Jonathan Corbet <corbet@lwn.net>,
        Willem de Bruijn <willemdebruijn.kernel@gmail.com>,
        "David S. Miller" <davem@davemloft.net>,
        Eric Dumazet <edumazet@google.com>,
        Jakub Kicinski <kuba@kernel.org>,
        Paolo Abeni <pabeni@redhat.com>,
        "Michael S. Tsirkin" <mst@redhat.com>,
        Xuan Zhuo <xuanzhuo@linux.alibaba.com>,
        Mykola Lysenko <mykolal@fb.com>, Shuah Khan <shuah@kernel.org>,
        bpf <bpf@vger.kernel.org>,
        "open list:DOCUMENTATION" <linux-doc@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Network Development <netdev@vger.kernel.org>,
        kvm@vger.kernel.org, virtualization@lists.linux-foundation.org,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@vger.kernel.org>,
        Yuri Benditovich <yuri.benditovich@daynix.com>,
        Andrew Melnychenko <andrew@daynix.com>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
Precedence: bulk

On Mon, Oct 16, 2023 at 7:38=E2=80=AFPM Jason Wang <jasowang@redhat.com> wr=
ote:
>
> On Tue, Oct 17, 2023 at 7:53=E2=80=AFAM Alexei Starovoitov
> <alexei.starovoitov@gmail.com> wrote:
> >
> > On Sun, Oct 15, 2023 at 10:10=E2=80=AFAM Akihiko Odaki <akihiko.odaki@d=
aynix.com> wrote:
> > >
> > > On 2023/10/16 1:07, Alexei Starovoitov wrote:
> > > > On Sun, Oct 15, 2023 at 7:17=E2=80=AFAM Akihiko Odaki <akihiko.odak=
i@daynix.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 sysc=
alls */
> > > >>          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 =3D {
> > > >> +       .get_func_proto         =3D sk_filter_func_proto,
> > > >> +       .is_valid_access        =3D sk_filter_is_valid_access,
> > > >> +       .convert_ctx_access     =3D bpf_convert_ctx_access,
> > > >> +       .gen_ld_abs             =3D 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 B=
PF
> > > and I'm worried if it may mean the interface stability.
> > >
> > > Let me describe the context. QEMU bundles an eBPF program that is use=
d
> > > 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 an=
d
> > > vhost_net. As such, the extension needs to be done in a way that ensu=
res
> > > 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?

It means that any new use of bpf has to be unstable for the time being.

> > 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.

Can we remove BPF_CGROUP_RUN_PROG_INET_INGRESS hook along
with BPF_PROG_TYPE_CGROUP_SKB program type?
Obviously not.
We can refactor it. We can move it around, but not remove.
That's the difference in stable vs unstable.