Re: [PATCH bpf-next 3/7] bpf: Add support for kprobe multi session cookie

[Jiri Olsa <olsajiri@gmail.com>]

On Tue, Apr 23, 2024 at 05:26:51PM -0700, Andrii Nakryiko wrote:
> On Mon, Apr 22, 2024 at 5:13 AM Jiri Olsa <jolsa@kernel.org> wrote:
> >
> > Adding support for cookie within the session of kprobe multi
> > entry and return program.
> >
> > The session cookie is u64 value and can be retrieved be new
> > kfunc bpf_session_cookie, which returns pointer to the cookie
> > value. The bpf program can use the pointer to store (on entry)
> > and load (on return) the value.
> >
> > The cookie value is implemented via fprobe feature that allows
> > to share values between entry and return ftrace fprobe callbacks.
> >
> > Signed-off-by: Jiri Olsa <jolsa@kernel.org>
> > ---
> >  kernel/bpf/verifier.c    |  7 +++++++
> >  kernel/trace/bpf_trace.c | 19 ++++++++++++++++---
> >  2 files changed, 23 insertions(+), 3 deletions(-)
> >
> 
> Had the same question as Alexei, but this read-write semantics quirk
> makes sense. But it's probably a bit more reliable and cleaner to
> handle it by special casing this kfunc a bit earlier (see
> KF_bpf_rbtree_add_impl) and setting r0_size = 8, r0_rdonly = false.
> And then let generic PTR -> INT logic kick in. You'll be futzing with
> register state much less.

ok, will try it this way

thanks,
jirka

> 
> Other than that looks good:
> 
> Acked-by: Andrii Nakryiko <andrii@kernel.org>
> 
> > diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> > index 68cfd6fc6ad4..baaca451aebc 100644
> > --- a/kernel/bpf/verifier.c
> > +++ b/kernel/bpf/verifier.c
> > @@ -10987,6 +10987,7 @@ enum special_kfunc_type {
> >         KF_bpf_percpu_obj_drop_impl,
> >         KF_bpf_throw,
> >         KF_bpf_iter_css_task_new,
> > +       KF_bpf_session_cookie,
> >  };
> 
> [...]