From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-177.mta0.migadu.com (out-177.mta0.migadu.com [91.218.175.177]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 0E5AC2E401 for ; Wed, 14 Jan 2026 02:25:46 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.177 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1768357548; cv=none; b=L8JP70eJWULuEt3FsMrIS1bo/pVwIsjvMZZx9EYtDENBJ60VmXLQaDd2dOHYjkvJquqPROeOsa1WzQsSqXZQqiQJl9s89IusUIqNGKHUN/iSjiI+fu+52gbwOmLiNfWZ1OgbDfk8mThfuQHXpvbC2gJn2sUgfj3Xh7ZGwtxhRno= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1768357548; c=relaxed/simple; bh=7QlruefSFU5VivGuOFlSA8UdtDYSuAMsvC7hc6oov/A=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=BVt3Qr5a/cQPq/3L0NwhX5KPIZPdIBNyd0yN3M+wVB4KVWaaeUeBTJ65l+v4vavLk1tjN3ImE72IDKDhpaEGPviIy0/LwJWv7QjYsMxTeVWwUGNT3T1ZMAnVe6ILqLq65vvQVsroCp5a/84upoJtyIGxRtw5N+DJegwRBw7QNBQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=MyGV5KzT; arc=none smtp.client-ip=91.218.175.177 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="MyGV5KzT" X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1768357544; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=ldPZx7QkOGGsRgh2JZ/aOzAveRu52NfE4WFpc0QdLIw=; b=MyGV5KzTcjT8TyG/sLGpxECcOuUnkb9247vIpHds8u4oE3EV3Vn6Tf+Km0zU7DOBBgTw7v FMCCgWlRVXePVtqoXYOjK6Jr866zIqf7SzVhMLsBqf6js8WFw6CBeYmU0sx4XHrknx8ha7 YoyQ55z6p27SsoJic2gTWVSywmkdf98= From: Menglong Dong To: Menglong Dong , Andrii Nakryiko Cc: ast@kernel.org, andrii@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, davem@davemloft.net, dsahern@kernel.org, tglx@linutronix.de, mingo@redhat.com, jiang.biao@linux.dev, bp@alien8.de, dave.hansen@linux.intel.com, x86@kernel.org, hpa@zytor.com, bpf@vger.kernel.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH bpf-next v9 04/11] bpf: support fsession for bpf_session_is_return Date: Wed, 14 Jan 2026 10:25:31 +0800 Message-ID: <9562692.CDJkKcVGEf@7940hx> In-Reply-To: References: <20260110141115.537055-1-dongml2@chinatelecom.cn> <20260110141115.537055-5-dongml2@chinatelecom.cn> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" X-Migadu-Flow: FLOW_OUT On 2026/1/14 09:22 Andrii Nakryiko write: > On Sat, Jan 10, 2026 at 6:12=E2=80=AFAM Menglong Dong wrote: > > > > If fsession exists, we will use the bit (1 << BPF_TRAMP_M_IS_RETURN) in > > ctx[-1] to store the "is_return" flag. > > > > The logic of bpf_session_is_return() for fsession is implemented in the > > verifier by inline following code: > > > > bool bpf_session_is_return(void *ctx) > > { > > return !!(((u64 *)ctx)[-1] & (1 << BPF_TRAMP_M_IS_RETURN)); >=20 > this look unnecessarily scary :) !! part is unnecessary because > non-zero integer will be converted to proper true(1)/false(0) by > compiler. But I'd just rewrite it in arguably slightly simpler form > that lays itself to assembly more directly: >=20 > return ((u64 *)ctx[-1] >> BPF_TRAMP_M_IS_RETURN) & 1; Yeah, the C code in the comment is wrong and not corresponding to the inline code. I'll update it in the next version. >=20 > > } > > [......] > > }; > > > > +#define BPF_TRAMP_M_NR_ARGS 0 > > +#define BPF_TRAMP_M_IS_RETURN 8 >=20 > nit: What does "M" stand for? Macro? Mask? Menglong? ;) Some new > convention, why? Ah, I think it stand for Mask. I'm not good at naming, and this word come to my mind when I want a prefix for the case ;) >=20 > > + > > struct bpf_tramp_links { > > struct bpf_tramp_link *links[BPF_MAX_TRAMP_LINKS]; > > int nr_links; > > diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c > > index bfff3f84fd91..1b0292a03186 100644 > > --- a/kernel/bpf/verifier.c > > +++ b/kernel/bpf/verifier.c > > @@ -12374,6 +12374,7 @@ enum special_kfunc_type { > > KF_bpf_arena_alloc_pages, > > KF_bpf_arena_free_pages, > > KF_bpf_arena_reserve_pages, > > + KF_bpf_session_is_return, > > }; > > > > BTF_ID_LIST(special_kfunc_list) > > @@ -12451,6 +12452,7 @@ BTF_ID(func, bpf_task_work_schedule_resume_impl) > > BTF_ID(func, bpf_arena_alloc_pages) > > BTF_ID(func, bpf_arena_free_pages) > > BTF_ID(func, bpf_arena_reserve_pages) > > +BTF_ID(func, bpf_session_is_return) > > > > static bool is_task_work_add_kfunc(u32 func_id) > > { > > @@ -12505,7 +12507,8 @@ get_kfunc_ptr_arg_type(struct bpf_verifier_env = *env, > > struct bpf_reg_state *reg =3D ®s[regno]; > > bool arg_mem_size =3D false; > > > > - if (meta->func_id =3D=3D special_kfunc_list[KF_bpf_cast_to_kern= _ctx]) > > + if (meta->func_id =3D=3D special_kfunc_list[KF_bpf_cast_to_kern= _ctx] || > > + meta->func_id =3D=3D special_kfunc_list[KF_bpf_session_is_r= eturn]) > > return KF_ARG_PTR_TO_CTX; > > > > if (argno + 1 < nargs && > > @@ -22558,6 +22561,16 @@ static int fixup_kfunc_call(struct bpf_verifie= r_env *env, struct bpf_insn *insn, > > desc->func_id =3D=3D special_kfunc_list[KF_bpf_rdonl= y_cast]) { > > insn_buf[0] =3D BPF_MOV64_REG(BPF_REG_0, BPF_REG_1); > > *cnt =3D 1; > > + } else if (desc->func_id =3D=3D special_kfunc_list[KF_bpf_sessi= on_is_return] && > > + env->prog->expected_attach_type =3D=3D BPF_TRACE_FSE= SSION) { > > + /* implement and inline the bpf_session_is_return() for >=20 > nit: comment style ACK >=20 > > + * fsession, and the logic is: > > + * return !!(((u64 *)ctx)[-1] & (1 << BPF_TRAMP_M_IS_= RETURN)) > > + */ > > + insn_buf[0] =3D BPF_LDX_MEM(BPF_DW, BPF_REG_0, BPF_REG_= 1, -8); > > + insn_buf[1] =3D BPF_ALU64_IMM(BPF_RSH, BPF_REG_0, BPF_T= RAMP_M_IS_RETURN); > > + insn_buf[2] =3D BPF_ALU64_IMM(BPF_AND, BPF_REG_0, 1); >=20 > lol, your assembly is simpler than that C expression above, let's keep > C close to what you actually are doing in assembler ACK >=20 > > + *cnt =3D 3; > > } > > > > if (env->insn_aux_data[insn_idx].arg_prog) { > > diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c > > index 297dcafb2c55..1fe508d451b7 100644 > > --- a/kernel/trace/bpf_trace.c > > +++ b/kernel/trace/bpf_trace.c > > @@ -3334,34 +3334,40 @@ __bpf_kfunc __u64 *bpf_session_cookie(void *ctx) > > > > __bpf_kfunc_end_defs(); > > > > -BTF_KFUNCS_START(kprobe_multi_kfunc_set_ids) > > +BTF_KFUNCS_START(session_kfunc_set_ids) > > BTF_ID_FLAGS(func, bpf_session_is_return) > > BTF_ID_FLAGS(func, bpf_session_cookie) > > -BTF_KFUNCS_END(kprobe_multi_kfunc_set_ids) > > +BTF_KFUNCS_END(session_kfunc_set_ids) > > > > -static int bpf_kprobe_multi_filter(const struct bpf_prog *prog, u32 kf= unc_id) > > +static int bpf_session_filter(const struct bpf_prog *prog, u32 kfunc_i= d) > > { > > - if (!btf_id_set8_contains(&kprobe_multi_kfunc_set_ids, kfunc_id= )) > > + if (!btf_id_set8_contains(&session_kfunc_set_ids, kfunc_id)) > > return 0; > > > > - if (!is_kprobe_session(prog) && !is_uprobe_session(prog)) > > + if (!is_kprobe_session(prog) && !is_uprobe_session(prog) && > > + prog->expected_attach_type !=3D BPF_TRACE_FSESSION) >=20 > check both expected_attach_type *and* prog_type, please (and I think > it would be good to check prog type for kprobe_session and > uprobe_session as well, because now it's not guaranteed that program > will be of BPF_PROG_TYPE_KPROBE OK, it make sense. I'll check the prog_type for all of them. Thanks! Menglong Dong >=20 >=20 > > return -EACCES; > > > > return 0; > > } > > > > -static const struct btf_kfunc_id_set bpf_kprobe_multi_kfunc_set =3D { > > +static const struct btf_kfunc_id_set bpf_session_kfunc_set =3D { > > .owner =3D THIS_MODULE, > > - .set =3D &kprobe_multi_kfunc_set_ids, > > - .filter =3D bpf_kprobe_multi_filter, > > + .set =3D &session_kfunc_set_ids, > > + .filter =3D bpf_session_filter, > > }; > > > > -static int __init bpf_kprobe_multi_kfuncs_init(void) > > +static int __init bpf_trace_kfuncs_init(void) > > { > > - return register_btf_kfunc_id_set(BPF_PROG_TYPE_KPROBE, &bpf_kpr= obe_multi_kfunc_set); > > + int err =3D 0; > > + > > + err =3D err ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_KPROBE, = &bpf_session_kfunc_set); > > + err =3D err ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_TRACING,= &bpf_session_kfunc_set); > > + > > + return err; > > } > > > > -late_initcall(bpf_kprobe_multi_kfuncs_init); > > +late_initcall(bpf_trace_kfuncs_init); > > > > typedef int (*copy_fn_t)(void *dst, const void *src, u32 size, struct = task_struct *tsk); > > > > -- > > 2.52.0 > > >=20