linux-kernel - Re: [PATCH sched_ext/for-6.15 v3 3/5] sched_ext: Add scx_kfunc_ids_ops_context_sensitive for unified filtering of context-sensitive SCX kfuncs

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Message-ID: <CAADnVQLkzX8dN9+Uk34idgxcD1rK639hnd8aZsz=0HJibpAwag@mail.gmail.com>
Date: Fri, 28 Feb 2025 15:06:32 -0800
From: Alexei Starovoitov <alexei.starovoitov@...il.com>
To: Tejun Heo <tj@...nel.org>
Cc: Juntong Deng <juntong.deng@...look.com>, Alexei Starovoitov <ast@...nel.org>, 
	Daniel Borkmann <daniel@...earbox.net>, John Fastabend <john.fastabend@...il.com>, 
	Andrii Nakryiko <andrii@...nel.org>, Martin KaFai Lau <martin.lau@...ux.dev>, Eddy Z <eddyz87@...il.com>, 
	Song Liu <song@...nel.org>, Yonghong Song <yonghong.song@...ux.dev>, KP Singh <kpsingh@...nel.org>, 
	Stanislav Fomichev <sdf@...ichev.me>, Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>, 
	Kumar Kartikeya Dwivedi <memxor@...il.com>, David Vernet <void@...ifault.com>, Andrea Righi <arighi@...dia.com>, 
	Changwoo Min <changwoo@...lia.com>, bpf <bpf@...r.kernel.org>, 
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH sched_ext/for-6.15 v3 3/5] sched_ext: Add
 scx_kfunc_ids_ops_context_sensitive for unified filtering of
 context-sensitive SCX kfuncs

On Fri, Feb 28, 2025 at 1:31 PM Tejun Heo <tj@...nel.org> wrote:
>
> Hello,
>
> On Thu, Feb 27, 2025 at 06:34:37PM -0800, Alexei Starovoitov wrote:
> > > Hmm... would that mean a non-sched_ext bpf prog would be able to call e.g.
> > > scx_bpf_dsq_insert()?
> >
> > Not as far as I can tell.
> > scx_kfunc_ids_unlocked[] doesn't include scx_bpf_dsq_insert.
> > It's part of scx_kfunc_ids_enqueue_dispatch[].
> >
> > So this bit in patch 3 enables it:
> > +       if ((flags & SCX_OPS_KF_ENQUEUE) &&
> > +           btf_id_set8_contains(&scx_kfunc_ids_enqueue_dispatch, kfunc_id))
> >
> > and in patch 2:
> > +       [SCX_OP_IDX(enqueue)]                   = SCX_OPS_KF_ENQUEUE,
> >
> > So scx_bpf_dsq_insert() kfunc can only be called out
> > of enqueue() sched-ext hook.
> >
> > So the restriction is still the same. afaict.
>
> Hmm... maybe I'm missing something:
>
>   static int scx_kfunc_ids_ops_context_sensitive_filter(const struct bpf_prog *prog, u32 kfunc_id)
>   {
>          u32 moff, flags;
>
>          // allow non-context sensitive kfuncs
>          if (!btf_id_set8_contains(&scx_kfunc_ids_ops_context_sensitive, kfunc_id))
>                  return 0;
>
>          // allow unlocked to be called form all SYSCALL progs
>          if (prog->type == BPF_PROG_TYPE_SYSCALL &&
>              btf_id_set8_contains(&scx_kfunc_ids_unlocked, kfunc_id))
>                  return 0;
>
>          // *** HERE, allow if the prog is not SCX ***
>          if (prog->type == BPF_PROG_TYPE_STRUCT_OPS &&
>              prog->aux->st_ops != &bpf_sched_ext_ops)

Ohh. You're right. My bad.
Here it probably needs
&& !!btf_id_set8_contains(&scx_kfunc_ids_ops_context_sensitive

since later scx_kfunc_set_ops_context_sensitive
is registered for all of struct-ops.