Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::3:3 as permitted sender) client-ip=2620:137:e000::3:3;
Message-ID: <664003d3-aadb-4938-80f6-67fab1c9dcdd@daynix.com>
Date:   Wed, 22 Nov 2023 14:36:32 +0900
MIME-Version: 1.0
User-Agent: Mozilla Thunderbird
Subject: Re: [RFC PATCH v2 1/7] bpf: Introduce BPF_PROG_TYPE_VNET_HASH
To:     Song Liu <song@kernel.org>
Cc:     Alexei Starovoitov <alexei.starovoitov@gmail.com>,
        Jason Wang <jasowang@redhat.com>,
        Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Andrii Nakryiko <andrii@kernel.org>,
        Martin KaFai Lau <martin.lau@linux.dev>,
        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>
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>
 <CAADnVQLt8NWvP8qGWMPx=12PwWWE69P7aS2dbm=khAJkCnJEoQ@mail.gmail.com>
 <9a4853ad-5ef4-4b15-a49e-9edb5ae4468e@daynix.com>
 <6253fb6b-9a53-484a-9be5-8facd46c051e@daynix.com>
 <CAPhsuW5JYoM-Mkehdy=FQsG1nvjbYGzwRZx8BkpG1P7cHdD=eQ@mail.gmail.com>
 <dba89d4b-84aa-4c9f-b016-56fd3ade04b2@daynix.com>
 <CAPhsuW5KLgt_gsih7zi+T99iYVbt7hk7=OCwYzin-H3=OhF54Q@mail.gmail.com>
 <a1f09866-a443-4f74-8025-6cdb32eb1d2c@daynix.com>
 <CAPhsuW4o5o41a+jVjgGP+Ck3eUD8w6coLXMTYewXKJYmciLLnQ@mail.gmail.com>
Content-Language: en-US
From:   Akihiko Odaki <akihiko.odaki@daynix.com>
In-Reply-To: <CAPhsuW4o5o41a+jVjgGP+Ck3eUD8w6coLXMTYewXKJYmciLLnQ@mail.gmail.com>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 8bit
Precedence: bulk

On 2023/11/22 14:25, Song Liu wrote:
> On Mon, Nov 20, 2023 at 12:05 AM Akihiko Odaki <akihiko.odaki@daynix.com> wrote:
>>
>> On 2023/11/20 6:02, Song Liu wrote:
> [...]
>>>> In contrast, our intended use case is more like a normal application.
>>>> So, for example, a user may download a container and run QEMU (including
>>>> the BPF program) installed in the container. As such, it is nice if the
>>>> ABI is stable across kernel releases, but it is not guaranteed for
>>>> kfuncs. Such a use case is already covered with the eBPF steering
>>>> program so I want to maintain it if possible.
>>>
>>> TBH, I don't think stability should be a concern for kfuncs used by QEMU.
>>> Many core BPF APIs are now implemented as kfuncs: bpf_dynptr_*,
>>> bpf_rcu_*, etc. As long as there are valid use cases,these kfuncs will
>>> be supported.
>>
>> Documentation/bpf/kfuncs.rst still says:
>>   > kfuncs provide a kernel <-> kernel API, and thus are not bound by any
>>   > of the strict stability restrictions associated with kernel <-> user
>>   > UAPIs.
>>
>> Is it possible to change the statement like as follows:
>> "Most kfuncs provide a kernel <-> kernel API, and thus are not bound by
>> any of the strict stability restrictions associated with kernel <-> user
>> UAPIs. kfuncs that have same stability restrictions associated with
>> UAPIs are exceptional, and must be carefully reviewed by subsystem (and
>> BPF?) maintainers as any other UAPIs are."
> 
> I am afraid this is against the intention to not guarantee UAPI-level stability
> for kfuncs.

Is it possible to ensure that a QEMU binary with the eBPF program 
included works on different kernel versions without UAPI-level stability 
then? Otherwise, I think we need to think of the minimal UAPI addition 
that exposes the feature I propose, and the two options I presented 
first are the candidates of such: the stable BPF change or tuntap 
interface change.

Regards,
Akihiko Odaki