[PATCH bpf-next v2 1/2] bpf: Print breakdown of insns processed by subprogs

[Paul Chaignon <paul.chaignon@gmail.com>]

When using global functions (i.e. subprogs), the verifier performs
function-by-function verification. In that case, the sum of the
instructions processed in each global function and in the main program
counts towards the 1 million instructions limit. Only that sum is
reported in the verifier logs.

While starting to use global functions in Cilium (finally!), we found it
can be useful to have the breakdown per global function, to understand
exactly where the budget is currently spent. This patch implements this
breakdown, under BPF_LOG_STATS, as done for the stack depths.

Signed-off-by: Paul Chaignon <paul.chaignon@gmail.com>
---
Changes in v2:
  - None for this patch.

 include/linux/bpf_verifier.h |  1 +
 kernel/bpf/verifier.c        | 14 ++++++++++++++
 2 files changed, 15 insertions(+)

diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h
index 101ca6cc5424..976e2b2f40e8 100644
--- a/include/linux/bpf_verifier.h
+++ b/include/linux/bpf_verifier.h
@@ -779,6 +779,7 @@ struct bpf_subprog_info {
 	u32 exit_idx; /* Index of one of the BPF_EXIT instructions in this subprogram */
 	u16 stack_depth; /* max. stack depth used by this function */
 	u16 stack_extra;
+	u32 insn_processed;
 	/* offsets in range [stack_depth .. fastcall_stack_off)
 	 * are used for bpf_fastcall spills and fills.
 	 */
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 03f9e16c2abe..b48389b48eb6 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -18183,6 +18183,7 @@ static int do_check_common(struct bpf_verifier_env *env, int subprog)
 	}
 
 	ret = do_check(env);
+
 out:
 	if (!ret && pop_log)
 		bpf_vlog_reset(&env->log, 0);
@@ -18215,6 +18216,7 @@ static int do_check_subprogs(struct bpf_verifier_env *env)
 	struct bpf_prog_aux *aux = env->prog->aux;
 	struct bpf_func_info_aux *sub_aux;
 	int i, ret, new_cnt;
+	u32 insn_processed;
 
 	if (!aux->func_info)
 		return 0;
@@ -18229,6 +18231,8 @@ static int do_check_subprogs(struct bpf_verifier_env *env)
 		if (!bpf_subprog_is_global(env, i))
 			continue;
 
+		insn_processed = env->insn_processed;
+
 		sub_aux = subprog_aux(env, i);
 		if (!sub_aux->called || sub_aux->verified)
 			continue;
@@ -18236,6 +18240,7 @@ static int do_check_subprogs(struct bpf_verifier_env *env)
 		env->insn_idx = env->subprog_info[i].start;
 		WARN_ON_ONCE(env->insn_idx == 0);
 		ret = do_check_common(env, i);
+		env->subprog_info[i].insn_processed = env->insn_processed - insn_processed;
 		if (ret) {
 			return ret;
 		} else if (env->log.level & BPF_LOG_LEVEL) {
@@ -18262,10 +18267,12 @@ static int do_check_subprogs(struct bpf_verifier_env *env)
 
 static int do_check_main(struct bpf_verifier_env *env)
 {
+	u32 insn_processed = env->insn_processed;
 	int ret;
 
 	env->insn_idx = 0;
 	ret = do_check_common(env, 0);
+	env->subprog_info[0].insn_processed = env->insn_processed - insn_processed;
 	if (!ret)
 		env->prog->aux->stack_depth = env->subprog_info[0].stack_depth;
 	return ret;
@@ -18288,6 +18295,13 @@ static void print_verification_stats(struct bpf_verifier_env *env)
 				verbose(env, "+");
 		}
 		verbose(env, "\n");
+		verbose(env, "insns processed %d", env->subprog_info[0].insn_processed);
+		for (i = 1; i < env->subprog_cnt; i++) {
+			if (!bpf_subprog_is_global(env, i))
+				continue;
+			verbose(env, "+%d", env->subprog_info[i].insn_processed);
+		}
+		verbose(env, "\n");
 	}
 	verbose(env, "processed %d insns (limit %d) max_states_per_insn %d "
 		"total_states %d peak_states %d mark_read %d\n",
-- 
2.43.0