bpf: add helper inlining infra and optimize map_array lookup

Optimize bpf_call -> bpf_map_lookup_elem() -> array_map_lookup_elem()
into a sequence of bpf instructions.
When JIT is on the sequence of bpf instructions is the sequence
of native cpu instructions with significantly faster performance
than indirect call and two function's prologue/epilogue.

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 62 insertions, 3 deletions

diff --git a/kernel/bpf/arraymap.c b/kernel/bpf/arraymap.c
index 6b6f41f0b211..bcf9955fac95 100644
--- a/kernel/bpf/arraymap.c
+++ b/kernel/bpf/arraymap.c
@@ -1,4 +1,5 @@
 /* Copyright (c) 2011-2014 PLUMgrid, http://plumgrid.com
+ * Copyright (c) 2016,2017 Facebook
  *
  * This program is free software; you can redistribute it and/or
  * modify it under the terms of version 2 of the GNU General Public
@@ -113,6 +114,33 @@ static void *array_map_lookup_elem(struct bpf_map *map, void *key)
 	return array->value + array->elem_size * index;
 }
 
+/* emit BPF instructions equivalent to C code of array_map_lookup_elem() */
+static u32 array_map_gen_lookup(struct bpf_map *map, struct bpf_insn *insn_buf)
+{
+	struct bpf_array *array = container_of(map, struct bpf_array, map);
+	struct bpf_insn *insn = insn_buf;
+	u32 elem_size = array->elem_size;
+	const int ret = BPF_REG_0;
+	const int map_ptr = BPF_REG_1;
+	const int index = BPF_REG_2;
+
+	*insn++ = BPF_ALU64_IMM(BPF_ADD, map_ptr, offsetof(struct bpf_array, value));
+	*insn++ = BPF_LDX_MEM(BPF_W, ret, index, 0);
+	*insn++ = BPF_JMP_IMM(BPF_JGE, ret, array->map.max_entries,
+			      elem_size == 1 ? 2 : 3);
+	if (elem_size == 1) {
+		/* nop */
+	} else if (is_power_of_2(elem_size)) {
+		*insn++ = BPF_ALU64_IMM(BPF_LSH, ret, ilog2(elem_size));
+	} else {
+		*insn++ = BPF_ALU64_IMM(BPF_MUL, ret, elem_size);
+	}
+	*insn++ = BPF_ALU64_REG(BPF_ADD, ret, map_ptr);
+	*insn++ = BPF_JMP_IMM(BPF_JA, 0, 0, 1);
+	*insn++ = BPF_MOV64_IMM(ret, 0);
+	return insn - insn_buf;
+}
+
 /* Called from eBPF program */
 static void *percpu_array_map_lookup_elem(struct bpf_map *map, void *key)
 {
@@ -267,6 +295,7 @@ static const struct bpf_map_ops array_ops = {
 	.map_lookup_elem = array_map_lookup_elem,
 	.map_update_elem = array_map_update_elem,
 	.map_delete_elem = array_map_delete_elem,
+	.map_gen_lookup = array_map_gen_lookup,
 };
 
 static struct bpf_map_type_list array_type __ro_after_init = {
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 2990fda1c6a5..90bf46787603 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -1273,7 +1273,7 @@ static void clear_all_pkt_pointers(struct bpf_verifier_env *env)
 	}
 }
 
-static int check_call(struct bpf_verifier_env *env, int func_id)
+static int check_call(struct bpf_verifier_env *env, int func_id, int insn_idx)
 {
 	struct bpf_verifier_state *state = &env->cur_state;
 	const struct bpf_func_proto *fn = NULL;
@@ -1369,6 +1369,7 @@ static int check_call(struct bpf_verifier_env *env, int func_id)
 		}
 		regs[BPF_REG_0].map_ptr = meta.map_ptr;
 		regs[BPF_REG_0].id = ++env->id_gen;
+		env->insn_aux_data[insn_idx].map_ptr = meta.map_ptr;
 	} else {
 		verbose("unknown return type %d of func %s#%d\n",
 			fn->ret_type, func_id_name(func_id), func_id);
@@ -2940,7 +2941,7 @@ static int do_check(struct bpf_verifier_env *env)
 					return -EINVAL;
 				}
 
-				err = check_call(env, insn->imm);
+				err = check_call(env, insn->imm, insn_idx);
 				if (err)
 					return err;
 
@@ -3268,6 +3269,7 @@ static int convert_ctx_accesses(struct bpf_verifier_env *env)
 }
 
 /* fixup insn->imm field of bpf_call instructions
+ * and inline eligible helpers as explicit sequence of BPF instructions
  *
  * this function is called after eBPF program passed verification
  */
@@ -3277,7 +3279,10 @@ static int fixup_bpf_calls(struct bpf_verifier_env *env)
 	struct bpf_insn *insn = prog->insnsi;
 	const struct bpf_func_proto *fn;
 	const int insn_cnt = prog->len;
-	int i;
+	struct bpf_insn insn_buf[16];
+	struct bpf_prog *new_prog;
+	struct bpf_map *map_ptr;
+	int i, cnt, delta = 0;
 
 	for (i = 0; i < insn_cnt; i++, insn++) {
 		if (insn->code != (BPF_JMP | BPF_CALL))
@@ -3300,6 +3305,31 @@ static int fixup_bpf_calls(struct bpf_verifier_env *env)
 			continue;
 		}
 
+		if (ebpf_jit_enabled() && insn->imm == BPF_FUNC_map_lookup_elem) {
+			map_ptr = env->insn_aux_data[i + delta].map_ptr;
+			if (!map_ptr->ops->map_gen_lookup)
+				goto patch_call_imm;
+
+			cnt = map_ptr->ops->map_gen_lookup(map_ptr, insn_buf);
+			if (cnt == 0 || cnt >= ARRAY_SIZE(insn_buf)) {
+				verbose("bpf verifier is misconfigured\n");
+				return -EINVAL;
+			}
+
+			new_prog = bpf_patch_insn_data(env, i + delta, insn_buf,
+						       cnt);
+			if (!new_prog)
+				return -ENOMEM;
+
+			delta += cnt - 1;
+
+			/* keep walking new program and skip insns we just inserted */
+			env->prog = prog = new_prog;
+			insn      = new_prog->insnsi + i + delta;
+			continue;
+		}
+
+patch_call_imm:
 		fn = prog->aux->ops->get_func_proto(insn->imm);
 		/* all functions that have prototype and verifier allowed
 		 * programs to call them, must be real in-kernel functions