linux-kernel - [PATCH bpf-next v3 1/3] bpf, x86: inline bpf_get_current_task() for x86

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Message-ID: <20260109082631.246647-2-dongml2@chinatelecom.cn>
Date: Fri,  9 Jan 2026 16:26:29 +0800
From: Menglong Dong <menglong8.dong@...il.com>
To: ast@...nel.org,
	eddyz87@...il.com
Cc: daniel@...earbox.net,
	john.fastabend@...il.com,
	andrii@...nel.org,
	martin.lau@...ux.dev,
	song@...nel.org,
	yonghong.song@...ux.dev,
	kpsingh@...nel.org,
	sdf@...ichev.me,
	haoluo@...gle.com,
	jolsa@...nel.org,
	bpf@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH bpf-next v3 1/3] bpf, x86: inline bpf_get_current_task() for x86_64

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>
---
v3:
- implement it in the verifier with BPF_MOV64_PERCPU_REG() instead of in
  x86_64 JIT.
---
 kernel/bpf/verifier.c | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 3d44c5d06623..520c413839ee 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 +23275,24 @@ 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)) {
+			insn_buf[0] = BPF_MOV64_IMM(BPF_REG_0, (u32)(unsigned long)&current_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);
+			cnt = 3;
+
+			new_prog = bpf_patch_insn_data(env, i + delta, insn_buf, cnt);
+			if (!new_prog)
+				return -ENOMEM;
+
+			delta    += cnt - 1;
+			env->prog = prog = new_prog;
+			insn      = new_prog->insnsi + i + delta;
+			goto next_insn;
+		}
 #endif
 		/* Implement bpf_get_func_arg inline. */
 		if (prog_type == BPF_PROG_TYPE_TRACING &&
-- 
2.52.0