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Message-ID: <CAADnVQLMztSfxCSxak900PVN+CtiN0FF=hkRcB8cHKiHipd4Dg@mail.gmail.com>
Date: Tue, 13 Jan 2026 09:50:09 -0800
From: Alexei Starovoitov <alexei.starovoitov@...il.com>
To: Menglong Dong <menglong8.dong@...il.com>
Cc: Alexei Starovoitov <ast@...nel.org>, Eduard <eddyz87@...il.com>,
Daniel Borkmann <daniel@...earbox.net>, John Fastabend <john.fastabend@...il.com>,
Andrii Nakryiko <andrii@...nel.org>, Martin KaFai Lau <martin.lau@...ux.dev>, 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>,
bpf <bpf@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH bpf-next v4 1/2] bpf, x86: inline bpf_get_current_task()
for x86_64
On Mon, Jan 12, 2026 at 2:45 AM Menglong Dong <menglong8.dong@...il.com> wrote:
>
> Inline bpf_get_current_task() and bpf_get_current_task_btf() for x86_64
> to obtain better performance.
>
> In !CONFIG_SMP case, the percpu variable is just a normal variable, and
> we can read the current_task directly.
>
> Signed-off-by: Menglong Dong <dongml2@...natelecom.cn>
> ---
> v4:
> - handle the !CONFIG_SMP case
>
> v3:
> - implement it in the verifier with BPF_MOV64_PERCPU_REG() instead of in
> x86_64 JIT.
> ---
> kernel/bpf/verifier.c | 29 +++++++++++++++++++++++++++++
> 1 file changed, 29 insertions(+)
>
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index 3d44c5d06623..12e99171afd8 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -17688,6 +17688,8 @@ static bool verifier_inlines_helper_call(struct bpf_verifier_env *env, s32 imm)
> switch (imm) {
> #ifdef CONFIG_X86_64
> case BPF_FUNC_get_smp_processor_id:
> + case BPF_FUNC_get_current_task_btf:
> + case BPF_FUNC_get_current_task:
> return env->prog->jit_requested && bpf_jit_supports_percpu_insn();
> #endif
> default:
> @@ -23273,6 +23275,33 @@ static int do_misc_fixups(struct bpf_verifier_env *env)
> insn = new_prog->insnsi + i + delta;
> goto next_insn;
> }
> +
> + /* Implement bpf_get_current_task() and bpf_get_current_task_btf() inline. */
> + if ((insn->imm == BPF_FUNC_get_current_task || insn->imm == BPF_FUNC_get_current_task_btf) &&
> + verifier_inlines_helper_call(env, insn->imm)) {
Though verifier_inlines_helper_call() gates this with CONFIG_X86_64,
I think we still need explicit:
#if defined(CONFIG_X86_64) && !defined(CONFIG_UML)
just like we did for BPF_FUNC_get_smp_processor_id.
Please check. I suspect UML will break without it.
> +#ifdef CONFIG_SMP
> + insn_buf[0] = BPF_MOV64_IMM(BPF_REG_0, (u32)(unsigned long)¤t_task);
> + insn_buf[1] = BPF_MOV64_PERCPU_REG(BPF_REG_0, BPF_REG_0);
> + insn_buf[2] = BPF_LDX_MEM(BPF_DW, BPF_REG_0, BPF_REG_0, 0);
> +#else
> + struct bpf_insn ld_current_addr[2] = {
> + BPF_LD_IMM64(BPF_REG_0, (unsigned long)¤t_task)
> + };
> + insn_buf[0] = ld_current_addr[0];
> + insn_buf[1] = ld_current_addr[1];
> + insn_buf[2] = BPF_LDX_MEM(BPF_DW, BPF_REG_0, BPF_REG_0, 0);
> +#endif
I wouldn't bother with !SMP.
If we need to add
On Mon, Jan 12, 2026 at 2:45 AM Menglong Dong <menglong8.dong@...il.com> wrote:
>
> Inline bpf_get_current_task() and bpf_get_current_task_btf() for x86_64
> to obtain better performance.
>
> In !CONFIG_SMP case, the percpu variable is just a normal variable, and
> we can read the current_task directly.
>
> Signed-off-by: Menglong Dong <dongml2@...natelecom.cn>
> ---
> v4:
> - handle the !CONFIG_SMP case
>
> v3:
> - implement it in the verifier with BPF_MOV64_PERCPU_REG() instead of in
> x86_64 JIT.
> ---
> kernel/bpf/verifier.c | 29 +++++++++++++++++++++++++++++
> 1 file changed, 29 insertions(+)
>
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index 3d44c5d06623..12e99171afd8 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -17688,6 +17688,8 @@ static bool verifier_inlines_helper_call(struct bpf_verifier_env *env, s32 imm)
> switch (imm) {
> #ifdef CONFIG_X86_64
> case BPF_FUNC_get_smp_processor_id:
> + case BPF_FUNC_get_current_task_btf:
> + case BPF_FUNC_get_current_task:
> return env->prog->jit_requested && bpf_jit_supports_percpu_insn();
> #endif
> default:
> @@ -23273,6 +23275,33 @@ static int do_misc_fixups(struct bpf_verifier_env *env)
> insn = new_prog->insnsi + i + delta;
> goto next_insn;
> }
> +
> + /* Implement bpf_get_current_task() and bpf_get_current_task_btf() inline. */
> + if ((insn->imm == BPF_FUNC_get_current_task || insn->imm == BPF_FUNC_get_current_task_btf) &&
> + verifier_inlines_helper_call(env, insn->imm)) {
Though verifier_inlines_helper_call() gates this with CONFIG_X86_64,
I think we still need explicit:
#if defined(CONFIG_X86_64) && !defined(CONFIG_UML)
just like we did for BPF_FUNC_get_smp_processor_id.
Please check. I suspect UML will break without it.
> +#ifdef CONFIG_SMP
> + insn_buf[0] = BPF_MOV64_IMM(BPF_REG_0, (u32)(unsigned long)¤t_task);
> + insn_buf[1] = BPF_MOV64_PERCPU_REG(BPF_REG_0, BPF_REG_0);
> + insn_buf[2] = BPF_LDX_MEM(BPF_DW, BPF_REG_0, BPF_REG_0, 0);
> +#else
> + struct bpf_insn ld_current_addr[2] = {
> + BPF_LD_IMM64(BPF_REG_0, (unsigned long)¤t_task)
> + };
> + insn_buf[0] = ld_current_addr[0];
> + insn_buf[1] = ld_current_addr[1];
> + insn_buf[2] = BPF_LDX_MEM(BPF_DW, BPF_REG_0, BPF_REG_0, 0);
> +#endif
I wouldn't bother with !SMP.
If we need to add
On Mon, Jan 12, 2026 at 2:45 AM Menglong Dong <menglong8.dong@...il.com> wrote:
>
> Inline bpf_get_current_task() and bpf_get_current_task_btf() for x86_64
> to obtain better performance.
>
> In !CONFIG_SMP case, the percpu variable is just a normal variable, and
> we can read the current_task directly.
>
> Signed-off-by: Menglong Dong <dongml2@...natelecom.cn>
> ---
> v4:
> - handle the !CONFIG_SMP case
>
> v3:
> - implement it in the verifier with BPF_MOV64_PERCPU_REG() instead of in
> x86_64 JIT.
> ---
> kernel/bpf/verifier.c | 29 +++++++++++++++++++++++++++++
> 1 file changed, 29 insertions(+)
>
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index 3d44c5d06623..12e99171afd8 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -17688,6 +17688,8 @@ static bool verifier_inlines_helper_call(struct bpf_verifier_env *env, s32 imm)
> switch (imm) {
> #ifdef CONFIG_X86_64
> case BPF_FUNC_get_smp_processor_id:
> + case BPF_FUNC_get_current_task_btf:
> + case BPF_FUNC_get_current_task:
> return env->prog->jit_requested && bpf_jit_supports_percpu_insn();
> #endif
> default:
> @@ -23273,6 +23275,33 @@ static int do_misc_fixups(struct bpf_verifier_env *env)
> insn = new_prog->insnsi + i + delta;
> goto next_insn;
> }
> +
> + /* Implement bpf_get_current_task() and bpf_get_current_task_btf() inline. */
> + if ((insn->imm == BPF_FUNC_get_current_task || insn->imm == BPF_FUNC_get_current_task_btf) &&
> + verifier_inlines_helper_call(env, insn->imm)) {
Though verifier_inlines_helper_call() gates this with CONFIG_X86_64,
I think we still need explicit:
#if defined(CONFIG_X86_64) && !defined(CONFIG_UML)
just like we did for BPF_FUNC_get_smp_processor_id.
Please check. I suspect UML will break without it.
> +#ifdef CONFIG_SMP
> + insn_buf[0] = BPF_MOV64_IMM(BPF_REG_0, (u32)(unsigned long)¤t_task);
> + insn_buf[1] = BPF_MOV64_PERCPU_REG(BPF_REG_0, BPF_REG_0);
> + insn_buf[2] = BPF_LDX_MEM(BPF_DW, BPF_REG_0, BPF_REG_0, 0);
> +#else
> + struct bpf_insn ld_current_addr[2] = {
> + BPF_LD_IMM64(BPF_REG_0, (unsigned long)¤t_task)
> + };
> + insn_buf[0] = ld_current_addr[0];
> + insn_buf[1] = ld_current_addr[1];
> + insn_buf[2] = BPF_LDX_MEM(BPF_DW, BPF_REG_0, BPF_REG_0, 0);
> +#endif
I wouldn't bother with !SMP.
If we need to add defined(CONFIG_X86_64) && !defined(CONFIG_UML)
I would add && defined(CONFIG_SMP) to it.
pw-bot: cr
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