[PATCH net-next v3 3/4] bpf: add helper bpf_perf_prog_read_value

From: Yonghong Song <hidden>
Date: 2017-09-18 23:05:55
Subsystem: bpf [general] (safe dynamic programs and tools), bpf [security & lsm] (security audit and enforcement using bpf), bpf [tracing], performance events subsystem, the rest, tracing · Maintainers: Alexei Starovoitov, Daniel Borkmann, Andrii Nakryiko, Eduard Zingerman, Kumar Kartikeya Dwivedi, KP Singh, Matt Bobrowski, Song Liu, Peter Zijlstra, Ingo Molnar, Arnaldo Carvalho de Melo, Namhyung Kim, Linus Torvalds, Steven Rostedt, Masami Hiramatsu

This patch adds helper bpf_perf_prog_read_cvalue for perf event based bpf
programs, to read event counter and enabled/running time.
The enabled/running time is accumulated since the perf event open.

The typical use case for perf event based bpf program is to attach itself
to a single event. In such cases, if it is desirable to get scaling factor
between two bpf invocations, users can can save the time values in a map,
and use the value from the map and the current value to calculate
the scaling factor.

Signed-off-by: Yonghong Song <redacted>
---
 include/linux/perf_event.h |  1 +
 include/uapi/linux/bpf.h   |  8 ++++++++
 kernel/events/core.c       |  1 +
 kernel/trace/bpf_trace.c   | 23 +++++++++++++++++++++++
 4 files changed, 33 insertions(+)

diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 13f08ee..5ff3055 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h

@@ -806,6 +806,7 @@ struct perf_output_handle {
 struct bpf_perf_event_data_kern {
 	struct pt_regs *regs;
 	struct perf_sample_data *data;
+	struct perf_event *event;
 };
 
 #ifdef CONFIG_CGROUP_PERF

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 2c68b9e..ba77022 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h

@@ -590,6 +590,13 @@ union bpf_attr {
  *     @buf: buf to fill
  *     @buf_size: size of the buf
  *     Return: 0 on success or negative error code
+ *
+ * int bpf_perf_prog_read_value(ctx, buf, buf_size)
+ *     read perf prog attached perf event counter and enabled/running time
+ *     @ctx: pointer to ctx
+ *     @buf: buf to fill
+ *     @buf_size: size of the buf
+ *     Return : 0 on success or negative error code
  */
 #define __BPF_FUNC_MAPPER(FN)		\
 	FN(unspec),			\

@@ -647,6 +654,7 @@ union bpf_attr {
 	FN(sk_redirect_map),		\
 	FN(sock_map_update),		\
 	FN(perf_event_read_value),		\
+	FN(perf_prog_read_value),		\
 
 /* integer value in 'imm' field of BPF_CALL instruction selects which helper
  * function eBPF program intends to call

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 2d5bbe5..d039086 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c

@@ -8081,6 +8081,7 @@ static void bpf_overflow_handler(struct perf_event *event,
 	struct bpf_perf_event_data_kern ctx = {
 		.data = data,
 		.regs = regs,
+		.event = event,
 	};
 	int ret = 0;

diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index 39ce5d9..596b5c9 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c

@@ -603,6 +603,18 @@ BPF_CALL_3(bpf_get_stackid_tp, void *, tp_buff, struct bpf_map *, map,
 			       flags, 0, 0);
 }
 
+BPF_CALL_3(bpf_perf_prog_read_value_tp, void *, ctx, struct bpf_perf_event_value *,
+	buf, u32, size)
+{
+	struct bpf_perf_event_data_kern *kctx = (struct bpf_perf_event_data_kern *)ctx;
+
+	if (size != sizeof(struct bpf_perf_event_value))
+		return -EINVAL;
+
+	return perf_event_read_local(kctx->event, &buf->counter, &buf->enabled,
+				     &buf->running);
+}
+
 static const struct bpf_func_proto bpf_get_stackid_proto_tp = {
 	.func		= bpf_get_stackid_tp,
 	.gpl_only	= true,

@@ -612,6 +624,15 @@ static const struct bpf_func_proto bpf_get_stackid_proto_tp = {
 	.arg3_type	= ARG_ANYTHING,
 };
 
+static const struct bpf_func_proto bpf_perf_prog_read_value_proto_tp = {
+         .func           = bpf_perf_prog_read_value_tp,
+         .gpl_only       = true,
+         .ret_type       = RET_INTEGER,
+         .arg1_type      = ARG_PTR_TO_CTX,
+         .arg2_type      = ARG_PTR_TO_UNINIT_MEM,
+         .arg3_type      = ARG_CONST_SIZE,
+};
+
 static const struct bpf_func_proto *tp_prog_func_proto(enum bpf_func_id func_id)
 {
 	switch (func_id) {

@@ -619,6 +640,8 @@ static const struct bpf_func_proto *tp_prog_func_proto(enum bpf_func_id func_id)
 		return &bpf_perf_event_output_proto_tp;
 	case BPF_FUNC_get_stackid:
 		return &bpf_get_stackid_proto_tp;
+	case BPF_FUNC_perf_prog_read_value:
+		return &bpf_perf_prog_read_value_proto_tp;
 	default:
 		return tracing_func_proto(func_id);
 	}

-- 
2.9.5

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