[PATCH v2 bpf-next 0/2] introduce BPF_F_PRESERVE_ELEMS

[PATCH v2 bpf-next 0/2] introduce BPF_F_PRESERVE_ELEMS

[Song Liu]

This set introduces BPF_F_PRESERVE_ELEMS to perf event array for better
sharing of perf event. By default, perf event array removes the perf event
when the map fd used to add the event is closed. With BPF_F_PRESERVE_ELEMS
set, however, the perf event will stay in the array until it is removed, or
the map is closed.

---
Changes v1 => v2:
1. Rename the flag as BPF_F_PRESERVE_ELEMS. (Alexei, Daniel)
2. Simplify the code and selftest. (Daniel, Alexei)

Song Liu (2):
  bpf: introduce BPF_F_PRESERVE_ELEMS for perf event array
  selftests/bpf: add tests for BPF_F_PRESERVE_ELEMS

 include/uapi/linux/bpf.h                      |  3 +
 kernel/bpf/arraymap.c                         | 21 +++++-
 tools/include/uapi/linux/bpf.h                |  3 +
 .../bpf/prog_tests/pe_preserve_elems.c        | 66 +++++++++++++++++++
 .../bpf/progs/test_pe_preserve_elems.c        | 44 +++++++++++++
 5 files changed, 135 insertions(+), 2 deletions(-)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/pe_preserve_elems.c
 create mode 100644 tools/testing/selftests/bpf/progs/test_pe_preserve_elems.c

--
2.24.1

[PATCH v2 bpf-next 1/2] bpf: introduce BPF_F_PRESERVE_ELEMS for perf event array

[Song Liu]

Currently, perf event in perf event array is removed from the array when
the map fd used to add the event is closed. This behavior makes it
difficult to the share perf events with perf event array.

Introduce perf event map that keeps the perf event open with a new flag
BPF_F_PRESERVE_ELEMS. With this flag set, perf events in the array are not
removed when the original map fd is closed. Instead, the perf event will
stay in the map until 1) it is explicitly removed from the array; or 2)
the array is freed.

Signed-off-by: Song Liu <songliubraving@fb.com>
---
 include/uapi/linux/bpf.h       |  3 +++
 kernel/bpf/arraymap.c          | 21 +++++++++++++++++++--
 tools/include/uapi/linux/bpf.h |  3 +++
 3 files changed, 25 insertions(+), 2 deletions(-)

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 82522f05c0213..ea78eb89f8d67 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -414,6 +414,9 @@ enum {
 
 /* Enable memory-mapping BPF map */
 	BPF_F_MMAPABLE		= (1U << 10),
+
+/* Share perf_event among processes */
+	BPF_F_PRESERVE_ELEMS	= (1U << 11),
 };
 
 /* Flags for BPF_PROG_QUERY. */
diff --git a/kernel/bpf/arraymap.c b/kernel/bpf/arraymap.c
index e5fd31268ae02..644ceb67350a6 100644
--- a/kernel/bpf/arraymap.c
+++ b/kernel/bpf/arraymap.c
@@ -15,7 +15,8 @@
 #include "map_in_map.h"
 
 #define ARRAY_CREATE_FLAG_MASK \
-	(BPF_F_NUMA_NODE | BPF_F_MMAPABLE | BPF_F_ACCESS_MASK)
+	(BPF_F_NUMA_NODE | BPF_F_MMAPABLE | BPF_F_ACCESS_MASK | \
+	 BPF_F_PRESERVE_ELEMS)
 
 static void bpf_array_free_percpu(struct bpf_array *array)
 {
@@ -64,6 +65,10 @@ int array_map_alloc_check(union bpf_attr *attr)
 	    attr->map_flags & BPF_F_MMAPABLE)
 		return -EINVAL;
 
+	if (attr->map_type != BPF_MAP_TYPE_PERF_EVENT_ARRAY &&
+	    attr->map_flags & BPF_F_PRESERVE_ELEMS)
+		return -EINVAL;
+
 	if (attr->value_size > KMALLOC_MAX_SIZE)
 		/* if value_size is bigger, the user space won't be able to
 		 * access the elements.
@@ -778,6 +783,15 @@ static int fd_array_map_delete_elem(struct bpf_map *map, void *key)
 	}
 }
 
+static void bpf_fd_array_map_clear(struct bpf_map *map);
+
+static void perf_event_fd_array_map_free(struct bpf_map *map)
+{
+	if (map->map_flags & BPF_F_PRESERVE_ELEMS)
+		bpf_fd_array_map_clear(map);
+	fd_array_map_free(map);
+}
+
 static void *prog_fd_array_get_ptr(struct bpf_map *map,
 				   struct file *map_file, int fd)
 {
@@ -1134,6 +1148,9 @@ static void perf_event_fd_array_release(struct bpf_map *map,
 	struct bpf_event_entry *ee;
 	int i;
 
+	if (map->map_flags & BPF_F_PRESERVE_ELEMS)
+		return;
+
 	rcu_read_lock();
 	for (i = 0; i < array->map.max_entries; i++) {
 		ee = READ_ONCE(array->ptrs[i]);
@@ -1148,7 +1165,7 @@ const struct bpf_map_ops perf_event_array_map_ops = {
 	.map_meta_equal = bpf_map_meta_equal,
 	.map_alloc_check = fd_array_map_alloc_check,
 	.map_alloc = array_map_alloc,
-	.map_free = fd_array_map_free,
+	.map_free = perf_event_fd_array_map_free,
 	.map_get_next_key = array_map_get_next_key,
 	.map_lookup_elem = fd_array_map_lookup_elem,
 	.map_delete_elem = fd_array_map_delete_elem,
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index 82522f05c0213..ea78eb89f8d67 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -414,6 +414,9 @@ enum {
 
 /* Enable memory-mapping BPF map */
 	BPF_F_MMAPABLE		= (1U << 10),
+
+/* Share perf_event among processes */
+	BPF_F_PRESERVE_ELEMS	= (1U << 11),
 };
 
 /* Flags for BPF_PROG_QUERY. */
-- 
2.24.1

[PATCH v2 bpf-next 2/2] selftests/bpf: add tests for BPF_F_PRESERVE_ELEMS

[Song Liu]

Add tests for perf event array with and without BPF_F_PRESERVE_ELEMS.

Add a perf event to array via fd mfd. Without BPF_F_PRESERVE_ELEMS, the
perf event is removed when mfd is closed. With BPF_F_PRESERVE_ELEMS, the
perf event is removed when the map is freed.

Signed-off-by: Song Liu <songliubraving@fb.com>
---
 .../bpf/prog_tests/pe_preserve_elems.c        | 66 +++++++++++++++++++
 .../bpf/progs/test_pe_preserve_elems.c        | 44 +++++++++++++
 2 files changed, 110 insertions(+)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/pe_preserve_elems.c
 create mode 100644 tools/testing/selftests/bpf/progs/test_pe_preserve_elems.c

diff --git a/tools/testing/selftests/bpf/prog_tests/pe_preserve_elems.c b/tools/testing/selftests/bpf/prog_tests/pe_preserve_elems.c
new file mode 100644
index 0000000000000..673d38395253b
--- /dev/null
+++ b/tools/testing/selftests/bpf/prog_tests/pe_preserve_elems.c
@@ -0,0 +1,66 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/* Copyright (c) 2019 Facebook */
+#include <test_progs.h>
+#include <linux/bpf.h>
+#include "test_pe_preserve_elems.skel.h"
+
+static int duration;
+
+static void test_one_map(struct bpf_map *map, struct bpf_program *prog,
+			 bool has_share_pe)
+{
+	int err, key = 0, pfd = -1, mfd = bpf_map__fd(map);
+	DECLARE_LIBBPF_OPTS(bpf_test_run_opts, opts);
+	struct perf_event_attr attr = {
+		.size = sizeof(struct perf_event_attr),
+		.type = PERF_TYPE_SOFTWARE,
+		.config = PERF_COUNT_SW_CPU_CLOCK,
+	};
+
+	pfd = syscall(__NR_perf_event_open, &attr, 0 /* pid */,
+		      -1 /* cpu 0 */, -1 /* group id */, 0 /* flags */);
+	if (CHECK(pfd < 0, "perf_event_open", "failed\n"))
+		return;
+
+	err = bpf_map_update_elem(mfd, &key, &pfd, BPF_ANY);
+	close(pfd);
+	if (CHECK(err < 0, "bpf_map_update_elem", "failed\n"))
+		return;
+
+	err = bpf_prog_test_run_opts(bpf_program__fd(prog), &opts);
+	if (CHECK(err < 0, "bpf_prog_test_run_opts", "failed\n"))
+		return;
+	if (CHECK(opts.retval != 0, "bpf_perf_event_read_value",
+		  "failed with %d\n", opts.retval))
+		return;
+
+	/* closing mfd, prog still holds a reference on map */
+	close(mfd);
+
+	err = bpf_prog_test_run_opts(bpf_program__fd(prog), &opts);
+	if (CHECK(err < 0, "bpf_prog_test_run_opts", "failed\n"))
+		return;
+
+	if (has_share_pe) {
+		CHECK(opts.retval != 0, "bpf_perf_event_read_value",
+		      "failed with %d\n", opts.retval);
+	} else {
+		CHECK(opts.retval != -ENOENT, "bpf_perf_event_read_value",
+		      "should have failed with %d, but got %d\n", -ENOENT,
+		      opts.retval);
+	}
+}
+
+void test_pe_preserve_elems(void)
+{
+	struct test_pe_preserve_elems *skel;
+
+	skel = test_pe_preserve_elems__open_and_load();
+	if (CHECK(!skel, "skel_open", "failed to open skeleton\n"))
+		return;
+
+	test_one_map(skel->maps.array_1, skel->progs.read_array_1, false);
+	test_one_map(skel->maps.array_2, skel->progs.read_array_2, true);
+
+	test_pe_preserve_elems__destroy(skel);
+}
diff --git a/tools/testing/selftests/bpf/progs/test_pe_preserve_elems.c b/tools/testing/selftests/bpf/progs/test_pe_preserve_elems.c
new file mode 100644
index 0000000000000..dc77e406de41f
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/test_pe_preserve_elems.c
@@ -0,0 +1,44 @@
+// SPDX-License-Identifier: GPL-2.0
+// Copyright (c) 2020 Facebook
+#include "vmlinux.h"
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_tracing.h>
+
+struct {
+	__uint(type, BPF_MAP_TYPE_PERF_EVENT_ARRAY);
+	__uint(max_entries, 1);
+	__uint(key_size, sizeof(int));
+	__uint(value_size, sizeof(int));
+} array_1 SEC(".maps");
+
+struct {
+	__uint(type, BPF_MAP_TYPE_PERF_EVENT_ARRAY);
+	__uint(max_entries, 1);
+	__uint(key_size, sizeof(int));
+	__uint(value_size, sizeof(int));
+	__uint(map_flags, BPF_F_PRESERVE_ELEMS);
+} array_2 SEC(".maps");
+
+SEC("raw_tp/sched_switch")
+int BPF_PROG(read_array_1)
+{
+	struct bpf_perf_event_value val;
+	long ret;
+
+	ret = bpf_perf_event_read_value(&array_1, 0, &val, sizeof(val));
+	bpf_printk("read_array_1 returns %ld", ret);
+	return ret;
+}
+
+SEC("raw_tp/task_rename")
+int BPF_PROG(read_array_2)
+{
+	struct bpf_perf_event_value val;
+	long ret;
+
+	ret = bpf_perf_event_read_value(&array_2, 0, &val, sizeof(val));
+	bpf_printk("read_array_2 returns %ld", ret);
+	return ret;
+}
+
+char LICENSE[] SEC("license") = "GPL";
-- 
2.24.1

Re: [PATCH v2 bpf-next 1/2] bpf: introduce BPF_F_PRESERVE_ELEMS for perf event array

[Daniel Borkmann]

On 9/29/20 11:56 PM, Song Liu wrote:
[...]
>   
> +static void bpf_fd_array_map_clear(struct bpf_map *map);
> +
> +static void perf_event_fd_array_map_free(struct bpf_map *map)
> +{
> +	if (map->map_flags & BPF_F_PRESERVE_ELEMS)
> +		bpf_fd_array_map_clear(map);
> +	fd_array_map_free(map);
> +}

Not quite sure why you place that here and added the fwd declaration? If you
place perf_event_fd_array_map_free() near perf_event_array_map_ops, then you
also don't need the additional bpf_fd_array_map_clear declaration.

>   static void *prog_fd_array_get_ptr(struct bpf_map *map,
>   				   struct file *map_file, int fd)
>   {
> @@ -1134,6 +1148,9 @@ static void perf_event_fd_array_release(struct bpf_map *map,
>   	struct bpf_event_entry *ee;
>   	int i;
>   
> +	if (map->map_flags & BPF_F_PRESERVE_ELEMS)
> +		return;
> +
>   	rcu_read_lock();
>   	for (i = 0; i < array->map.max_entries; i++) {
>   		ee = READ_ONCE(array->ptrs[i]);
> @@ -1148,7 +1165,7 @@ const struct bpf_map_ops perf_event_array_map_ops = {
>   	.map_meta_equal = bpf_map_meta_equal,
>   	.map_alloc_check = fd_array_map_alloc_check,
>   	.map_alloc = array_map_alloc,
> -	.map_free = fd_array_map_free,
> +	.map_free = perf_event_fd_array_map_free,
>   	.map_get_next_key = array_map_get_next_key,
>   	.map_lookup_elem = fd_array_map_lookup_elem,
>   	.map_delete_elem = fd_array_map_delete_elem,
> diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
> index 82522f05c0213..ea78eb89f8d67 100644
> --- a/tools/include/uapi/linux/bpf.h
> +++ b/tools/include/uapi/linux/bpf.h
> @@ -414,6 +414,9 @@ enum {
>   
>   /* Enable memory-mapping BPF map */
>   	BPF_F_MMAPABLE		= (1U << 10),
> +
> +/* Share perf_event among processes */
> +	BPF_F_PRESERVE_ELEMS	= (1U << 11),
>   };
>   
>   /* Flags for BPF_PROG_QUERY. */
> 

Re: [PATCH v2 bpf-next 1/2] bpf: introduce BPF_F_PRESERVE_ELEMS for perf event array

[Song Liu]

> On Sep 30, 2020, at 7:49 AM, Daniel Borkmann <daniel@iogearbox.net> wrote:
> 
> On 9/29/20 11:56 PM, Song Liu wrote:
> [...]
>>  +static void bpf_fd_array_map_clear(struct bpf_map *map);
>> +
>> +static void perf_event_fd_array_map_free(struct bpf_map *map)
>> +{
>> +	if (map->map_flags & BPF_F_PRESERVE_ELEMS)
>> +		bpf_fd_array_map_clear(map);
>> +	fd_array_map_free(map);
>> +}
> 
> Not quite sure why you place that here and added the fwd declaration? If you
> place perf_event_fd_array_map_free() near perf_event_array_map_ops, then you
> also don't need the additional bpf_fd_array_map_clear declaration.

Yeah.. I misread the line number...

Fixing it in v3.

Thanks,
Song