netdev - [PATCH bpf-next v2 1/2] bpf, x86: inline bpf_get_current_task() for x86

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Message-ID: <20260104131635.27621-2-dongml2@chinatelecom.cn>
Date: Sun,  4 Jan 2026 21:16:34 +0800
From: Menglong Dong <menglong8.dong@...il.com>
To: ast@...nel.org,
	eddyz87@...il.com
Cc: davem@...emloft.net,
	dsahern@...nel.org,
	daniel@...earbox.net,
	andrii@...nel.org,
	martin.lau@...ux.dev,
	song@...nel.org,
	yonghong.song@...ux.dev,
	john.fastabend@...il.com,
	kpsingh@...nel.org,
	sdf@...ichev.me,
	haoluo@...gle.com,
	jolsa@...nel.org,
	tglx@...utronix.de,
	mingo@...hat.com,
	bp@...en8.de,
	dave.hansen@...ux.intel.com,
	x86@...nel.org,
	hpa@...or.com,
	netdev@...r.kernel.org,
	bpf@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH bpf-next v2 1/2] 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. The instruction we use here is:

  65 48 8B 04 25 [offset] // mov rax, gs:[offset]

Signed-off-by: Menglong Dong <dongml2@...natelecom.cn>
---
v2:
- check the variable type in emit_ldx_percpu_r0 with __verify_pcpu_ptr
- remove the usage of const_current_task
---
 arch/x86/net/bpf_jit_comp.c | 36 ++++++++++++++++++++++++++++++++++++
 1 file changed, 36 insertions(+)

diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
index e3b1c4b1d550..f5ff7c77aad7 100644
--- a/arch/x86/net/bpf_jit_comp.c
+++ b/arch/x86/net/bpf_jit_comp.c
@@ -1300,6 +1300,25 @@ static void emit_st_r12(u8 **pprog, u32 size, u32 dst_reg, int off, int imm)
 	emit_st_index(pprog, size, dst_reg, X86_REG_R12, off, imm);
 }
 
+static void __emit_ldx_percpu_r0(u8 **pprog, __force unsigned long ptr)
+{
+	u8 *prog = *pprog;
+
+	/* mov rax, gs:[ptr] */
+	EMIT2(0x65, 0x48);
+	EMIT2(0x8B, 0x04);
+	EMIT1(0x25);
+	EMIT((u32)ptr, 4);
+
+	*pprog = prog;
+}
+
+#define emit_ldx_percpu_r0(prog, variable)					\
+	do {									\
+		__verify_pcpu_ptr(&(variable));					\
+		__emit_ldx_percpu_r0(&prog, (__force unsigned long)&(variable));\
+	} while (0)
+
 static int emit_atomic_rmw(u8 **pprog, u32 atomic_op,
 			   u32 dst_reg, u32 src_reg, s16 off, u8 bpf_size)
 {
@@ -2441,6 +2460,12 @@ st:			if (is_imm8(insn->off))
 		case BPF_JMP | BPF_CALL: {
 			u8 *ip = image + addrs[i - 1];
 
+			if (insn->src_reg == 0 && (insn->imm == BPF_FUNC_get_current_task ||
+						   insn->imm == BPF_FUNC_get_current_task_btf)) {
+				emit_ldx_percpu_r0(prog, current_task);
+				break;
+			}
+
 			func = (u8 *) __bpf_call_base + imm32;
 			if (src_reg == BPF_PSEUDO_CALL && tail_call_reachable) {
 				LOAD_TAIL_CALL_CNT_PTR(stack_depth);
@@ -4082,3 +4107,14 @@ bool bpf_jit_supports_timed_may_goto(void)
 {
 	return true;
 }
+
+bool bpf_jit_inlines_helper_call(s32 imm)
+{
+	switch (imm) {
+	case BPF_FUNC_get_current_task:
+	case BPF_FUNC_get_current_task_btf:
+		return true;
+	default:
+		return false;
+	}
+}
-- 
2.52.0