From: Menglong Dong <menglong.dong@linux•dev>
To: Menglong Dong <menglong8.dong@gmail•com>,
Andrii Nakryiko <andrii.nakryiko@gmail•com>
Cc: ast@kernel•org, andrii@kernel•org, davem@davemloft•net,
dsahern@kernel•org, daniel@iogearbox•net, martin.lau@linux•dev,
eddyz87@gmail•com, song@kernel•org, yonghong.song@linux•dev,
john.fastabend@gmail•com, kpsingh@kernel•org, sdf@fomichev•me,
haoluo@google•com, jolsa@kernel•org, tglx@linutronix•de,
mingo@redhat•com, bp@alien8•de, dave.hansen@linux•intel.com,
x86@kernel•org, hpa@zytor•com, netdev@vger•kernel.org,
bpf@vger•kernel.org, linux-kernel@vger•kernel.org
Subject: Re: [PATCH bpf-next v4 4/9] bpf: add the kfunc bpf_fsession_cookie
Date: Fri, 19 Dec 2025 09:31:05 +0800 [thread overview]
Message-ID: <2334439.iZASKD2KPV@7940hx> (raw)
In-Reply-To: <CAEf4Bza=Cuu-3LZs7XuK-d7FLKAU8ppkLneiuLqDejzfweHqqA@mail.gmail.com>
On 2025/12/19 08:55 Andrii Nakryiko <andrii.nakryiko@gmail•com> write:
> On Wed, Dec 17, 2025 at 1:55 AM Menglong Dong <menglong8.dong@gmail•com> wrote:
> >
> > Implement session cookie for fsession. In order to limit the stack usage,
> > we make 4 as the maximum of the cookie count.
> >
> > The offset of the current cookie is stored in the
> > "(ctx[-1] >> BPF_TRAMP_M_COOKIE) & 0xFF". Therefore, we can get the
> > session cookie with ctx[-offset].
> >
> > The stack will look like this:
> >
> > return value -> 8 bytes
> > argN -> 8 bytes
> > ...
> > arg1 -> 8 bytes
> > nr_args -> 8 bytes
> > ip(optional) -> 8 bytes
> > cookie2 -> 8 bytes
> > cookie1 -> 8 bytes
> >
> > Inline the bpf_fsession_cookie() in the verifer too.
> >
> > Signed-off-by: Menglong Dong <dongml2@chinatelecom•cn>
> > ---
> > v4:
> > - limit the maximum of the cookie count to 4
> > - store the session cookies before nr_regs in stack
> > ---
> > include/linux/bpf.h | 16 ++++++++++++++++
> > kernel/bpf/trampoline.c | 14 +++++++++++++-
> > kernel/bpf/verifier.c | 20 ++++++++++++++++++--
> > kernel/trace/bpf_trace.c | 9 +++++++++
> > 4 files changed, 56 insertions(+), 3 deletions(-)
> >
> > diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> > index d165ace5cc9b..0f35c6ab538c 100644
> > --- a/include/linux/bpf.h
> > +++ b/include/linux/bpf.h
> > @@ -1215,6 +1215,7 @@ enum {
> >
> > #define BPF_TRAMP_M_NR_ARGS 0
> > #define BPF_TRAMP_M_IS_RETURN 8
> > +#define BPF_TRAMP_M_COOKIE 9
> >
> > struct bpf_tramp_links {
> > struct bpf_tramp_link *links[BPF_MAX_TRAMP_LINKS];
> > @@ -1318,6 +1319,7 @@ struct bpf_trampoline {
> > struct mutex mutex;
> > refcount_t refcnt;
> > u32 flags;
> > + int cookie_cnt;
>
> can't you just count this each time you need to know instead of
> keeping track of this? it's not that expensive and won't happen that
> frequently (and we keep lock on trampoline, so it's also safe and
> race-free to count)
There is a for-loop below that use the "cookie_cnt" to clear all the
cookie to zero. We limited the maximum of cookie_cnt to 4, so
I guess we can count it directly there. I'll change it in the
next version.
Thanks!
Menglong Dong
>
> > u64 key;
> > struct {
> > struct btf_func_model model;
> > @@ -1762,6 +1764,7 @@ struct bpf_prog {
> > enforce_expected_attach_type:1, /* Enforce expected_attach_type checking at attach time */
> > call_get_stack:1, /* Do we call bpf_get_stack() or bpf_get_stackid() */
> > call_get_func_ip:1, /* Do we call get_func_ip() */
> > + call_session_cookie:1, /* Do we call bpf_fsession_cookie() */
> > tstamp_type_access:1, /* Accessed __sk_buff->tstamp_type */
> > sleepable:1; /* BPF program is sleepable */
> > enum bpf_prog_type type; /* Type of BPF program */
>
> [...]
>
next prev parent reply other threads:[~2025-12-19 1:31 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-12-17 9:54 [PATCH bpf-next v4 0/9] bpf: tracing session supporting Menglong Dong
2025-12-17 9:54 ` [PATCH bpf-next v4 1/9] bpf: add tracing session support Menglong Dong
2025-12-19 0:55 ` Andrii Nakryiko
2025-12-19 1:24 ` Menglong Dong
2025-12-17 9:54 ` [PATCH bpf-next v4 2/9] bpf: use last 8-bits for the nr_args in trampoline Menglong Dong
2025-12-17 9:54 ` [PATCH bpf-next v4 3/9] bpf: add the kfunc bpf_fsession_is_return Menglong Dong
2025-12-17 9:54 ` [PATCH bpf-next v4 4/9] bpf: add the kfunc bpf_fsession_cookie Menglong Dong
2025-12-19 0:55 ` Andrii Nakryiko
2025-12-19 1:31 ` Menglong Dong [this message]
2025-12-19 12:01 ` Menglong Dong
2025-12-17 9:54 ` [PATCH bpf-next v4 5/9] bpf,x86: introduce emit_st_r0_imm64() for trampoline Menglong Dong
2025-12-17 9:54 ` [PATCH bpf-next v4 6/9] bpf,x86: add tracing session supporting for x86_64 Menglong Dong
2025-12-19 0:55 ` Andrii Nakryiko
2025-12-19 1:41 ` Menglong Dong
2025-12-19 16:56 ` Andrii Nakryiko
2025-12-17 9:54 ` [PATCH bpf-next v4 7/9] libbpf: add support for tracing session Menglong Dong
2025-12-19 0:55 ` Andrii Nakryiko
2025-12-19 1:42 ` Menglong Dong
2025-12-17 9:54 ` [PATCH bpf-next v4 8/9] selftests/bpf: add testcases " Menglong Dong
2025-12-17 10:24 ` bot+bpf-ci
2025-12-17 11:42 ` Menglong Dong
2025-12-17 9:54 ` [PATCH bpf-next v4 9/9] selftests/bpf: test fsession mixed with fentry and fexit Menglong Dong
2025-12-17 10:24 ` bot+bpf-ci
2025-12-17 10:37 ` Menglong Dong
2025-12-19 0:55 ` [PATCH bpf-next v4 0/9] bpf: tracing session supporting Andrii Nakryiko
2025-12-19 1:18 ` Menglong Dong
2025-12-19 16:55 ` Andrii Nakryiko
2025-12-20 1:12 ` Menglong Dong
2025-12-20 9:01 ` Menglong Dong
2025-12-20 12:22 ` Menglong Dong
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