[PATCH bpf-next v4 1/2] bpf, x86: inline bpf_get_current_task() for x86_64

[Menglong Dong]

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@xxxxxxxxxxxxxxx>
---
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)) {
+#ifdef CONFIG_SMP
+			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);
+#else
+			struct bpf_insn ld_current_addr[2] = {
+				BPF_LD_IMM64(BPF_REG_0, (unsigned long)&current_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
+			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