netdev - Re: [PATCH bpf-next v6 00/10] bpf: fsession support

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Message-ID: <8625659.T7Z3S40VBb@7940hx>
Date: Tue, 06 Jan 2026 15:10:53 +0800
From: Menglong Dong <menglong.dong@...ux.dev>
To: Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc: Menglong Dong <menglong8.dong@...il.com>,
 Andrii Nakryiko <andrii.nakryiko@...il.com>,
 Alexei Starovoitov <ast@...nel.org>, Andrii Nakryiko <andrii@...nel.org>,
 Daniel Borkmann <daniel@...earbox.net>,
 Martin KaFai Lau <martin.lau@...ux.dev>, Eduard <eddyz87@...il.com>,
 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@...ichev.me>, Hao Luo <haoluo@...gle.com>,
 Jiri Olsa <jolsa@...nel.org>, "David S. Miller" <davem@...emloft.net>,
 David Ahern <dsahern@...nel.org>, Thomas Gleixner <tglx@...utronix.de>,
 Ingo Molnar <mingo@...hat.com>, jiang.biao@...ux.dev,
 Borislav Petkov <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>,
 X86 ML <x86@...nel.org>, "H. Peter Anvin" <hpa@...or.com>,
 bpf <bpf@...r.kernel.org>, Network Development <netdev@...r.kernel.org>,
 LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH bpf-next v6 00/10] bpf: fsession support

On 2026/1/6 12:20 Alexei Starovoitov <alexei.starovoitov@...il.com> write:
> On Mon, Jan 5, 2026 at 7:05 PM Menglong Dong <menglong.dong@...ux.dev> wrote:
> >
> > On 2026/1/6 05:20 Andrii Nakryiko <andrii.nakryiko@...il.com> write:
> > > On Sun, Jan 4, 2026 at 4:28 AM Menglong Dong <menglong8.dong@...il.com> wrote:
> > > >
> > > > Hi, all.
> > > >
> > [......]
> > > > Maybe it's possible to reuse the existing bpf_session_cookie() and
> > > > bpf_session_is_return(). First, we move the nr_regs from stack to struct
> > > > bpf_tramp_run_ctx, as Andrii suggested before. Then, we define the session
> > > > cookies as flexible array in bpf_tramp_run_ctx like this:
> > > >     struct bpf_tramp_run_ctx {
> > > >         struct bpf_run_ctx run_ctx;
> > > >         u64 bpf_cookie;
> > > >         struct bpf_run_ctx *saved_run_ctx;
> > > >         u64 func_meta; /* nr_args, cookie_index, etc */
> > > >         u64 fsession_cookies[];
> > > >     };
> > > >
> > > > The problem of this approach is that we can't inlined the bpf helper
> > > > anymore, such as get_func_arg, get_func_ret, get_func_arg_cnt, etc, as
> > > > we can't use the "current" in BPF assembly.
> > > >
> > >
> > > We can, as Alexei suggested on your other patch set. Is this still a
> > > valid concern?
> >
> > Yeah, with the support of BPF_MOV64_PERCPU_REG, it's much easier
> > now.
> >
> > So what approach should I use now? Change the prototype of
> > bpf_session_is_return/bpf_session_cookie, as Alexei suggested, or
> > use the approach here? I think both works, and I'm a little torn
> > now. Any suggestions?
> 
> I think adding 'void *ctx' to existing kfuncs makes tramp-based
> kfuncs faster, since less work needs to be done to store/read
> the same data from run_ctx/current.
> So that's my preference.

Okay, I'll implement it this way in the next version.

Thanks!
Menglong Dong