bpf: inline bpf_get_smp_processor_id() helper

If BPF JIT supports per-CPU MOV instruction, inline bpf_get_smp_processor_id()
to eliminate unnecessary function calls.
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Link: https://lore.kernel.org/r/20240402021307.1012571-3-andrii@kernel.orgSigned-off-by: Alexei Starovoitov <ast@kernel.org>

kernel/bpf/verifier.c

@@ -20074,6 +20074,30 @@ static int do_misc_fixups(struct bpf_verifier_env *env)
 			goto next_insn;
 		}
 
+#ifdef CONFIG_X86_64
+		/* Implement bpf_get_smp_processor_id() inline. */
+		if (insn->imm == BPF_FUNC_get_smp_processor_id &&
+		    prog->jit_requested && bpf_jit_supports_percpu_insn()) {
+			/* BPF_FUNC_get_smp_processor_id inlining is an
+			 * optimization, so if pcpu_hot.cpu_number is ever
+			 * changed in some incompatible and hard to support
+			 * way, it's fine to back out this inlining logic
+			 */
+			insn_buf[0] = BPF_MOV32_IMM(BPF_REG_0, (u32)(unsigned long)&pcpu_hot.cpu_number);
+			insn_buf[1] = BPF_MOV64_PERCPU_REG(BPF_REG_0, BPF_REG_0);
+			insn_buf[2] = BPF_LDX_MEM(BPF_W, 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 &&
 		    insn->imm == BPF_FUNC_get_func_arg) {