[PATCH bpf-next] selftests/bpf: Add a test for mmap-able map in map

[PATCH bpf-next] selftests/bpf: Add a test for mmap-able map in map

[Song Liu]

Regular BPF hash map is not mmap-able from user space. However, map-in-map
with outer map of type BPF_MAP_TYPE_HASH_OF_MAPS and mmap-able array as
inner map can perform similar operations as a mmap-able hash map. This
can be used by applications that benefit from fast accesses to some local
data.

Add a selftest to show this use case.

Signed-off-by: Song Liu <song@kernel.org>
---
 .../bpf/prog_tests/test_mmap_inner_array.c    | 57 ++++++++++++++++++
 .../selftests/bpf/progs/mmap_inner_array.c    | 59 +++++++++++++++++++
 2 files changed, 116 insertions(+)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/test_mmap_inner_array.c
 create mode 100644 tools/testing/selftests/bpf/progs/mmap_inner_array.c

diff --git a/tools/testing/selftests/bpf/prog_tests/test_mmap_inner_array.c b/tools/testing/selftests/bpf/prog_tests/test_mmap_inner_array.c
new file mode 100644
index 000000000000..ce745776ed18
--- /dev/null
+++ b/tools/testing/selftests/bpf/prog_tests/test_mmap_inner_array.c
@@ -0,0 +1,57 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2024 Meta Platforms, Inc. and affiliates. */
+#include <test_progs.h>
+#include <sys/mman.h>
+#include "mmap_inner_array.skel.h"
+
+void test_mmap_inner_array(void)
+{
+	const long page_size = sysconf(_SC_PAGE_SIZE);
+	struct mmap_inner_array *skel;
+	int inner_array_fd, err;
+	void *tmp;
+	__u64 *val;
+
+	skel = mmap_inner_array__open_and_load();
+
+	if (!ASSERT_OK_PTR(skel, "open_and_load"))
+		return;
+
+	inner_array_fd = bpf_map__fd(skel->maps.inner_array);
+	tmp = mmap(NULL, page_size, PROT_READ | PROT_WRITE, MAP_SHARED, inner_array_fd, 0);
+	if (!ASSERT_OK_PTR(tmp, "inner array mmap"))
+		goto out;
+	val = (void *)tmp;
+
+	err = mmap_inner_array__attach(skel);
+	if (!ASSERT_OK(err, "attach"))
+		goto out_unmap;
+
+	skel->bss->pid = getpid();
+	usleep(1);
+
+	/* pid is set, pid_match == true and outer_map_match == false */
+	ASSERT_TRUE(skel->bss->pid_match, "pid match 1");
+	ASSERT_FALSE(skel->bss->outer_map_match, "outer map match 1");
+	ASSERT_FALSE(skel->bss->done, "done 1");
+	ASSERT_EQ(*val, 0, "value match 1");
+
+	err = bpf_map__update_elem(skel->maps.outer_map,
+				   &skel->bss->pid, sizeof(skel->bss->pid),
+				   &inner_array_fd, sizeof(inner_array_fd),
+				   BPF_ANY);
+	if (!ASSERT_OK(err, "update elem"))
+		goto out_unmap;
+	usleep(1);
+
+	/* outer map key is set, outer_map_match == true */
+	ASSERT_TRUE(skel->bss->pid_match, "pid match 2");
+	ASSERT_TRUE(skel->bss->outer_map_match, "outer map match 2");
+	ASSERT_TRUE(skel->bss->done, "done 2");
+	ASSERT_EQ(*val, skel->data->match_value, "value match 2");
+
+out_unmap:
+	munmap(tmp, page_size);
+out:
+	mmap_inner_array__destroy(skel);
+}
diff --git a/tools/testing/selftests/bpf/progs/mmap_inner_array.c b/tools/testing/selftests/bpf/progs/mmap_inner_array.c
new file mode 100644
index 000000000000..db8ca2aa4347
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/mmap_inner_array.c
@@ -0,0 +1,59 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2024 Meta Platforms, Inc. and affiliates. */
+
+#include "vmlinux.h"
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_tracing.h>
+
+#include "bpf_misc.h"
+#include "bpf_experimental.h"
+
+char _license[] SEC("license") = "GPL";
+
+struct inner_array_type {
+	__uint(type, BPF_MAP_TYPE_ARRAY);
+	__uint(map_flags, BPF_F_MMAPABLE);
+	__type(key, __u32);
+	__type(value, __u64);
+	__uint(max_entries, 1);
+} inner_array SEC(".maps");
+
+struct {
+	__uint(type, BPF_MAP_TYPE_HASH_OF_MAPS);
+	__uint(key_size, 4);
+	__uint(value_size, 4);
+	__uint(max_entries, 1);
+	__array(values, struct inner_array_type);
+} outer_map SEC(".maps");
+
+int pid = 0;
+__u64 match_value = 0x13572468;
+bool done = false;
+bool pid_match = false;
+bool outer_map_match = false;
+
+SEC("fentry/" SYS_PREFIX "sys_nanosleep")
+int add_to_list_in_inner_array(void *ctx)
+{
+	__u32 curr_pid, zero = 0;
+	struct bpf_map *map;
+	__u64 *value;
+
+	curr_pid = (u32)bpf_get_current_pid_tgid();
+	if (done || curr_pid != pid)
+		return 0;
+
+	pid_match = true;
+	map = bpf_map_lookup_elem(&outer_map, &curr_pid);
+	if (!map)
+		return 0;
+
+	outer_map_match = true;
+	value = bpf_map_lookup_elem(map, &zero);
+	if (!value)
+		return 0;
+
+	*value = match_value;
+	done = true;
+	return 0;
+}
-- 
2.43.0

Re: [PATCH bpf-next] selftests/bpf: Add a test for mmap-able map in map

[bot+bpf-ci]

[-- Attachment #1: Type: text/plain, Size: 532 bytes --]

Dear patch submitter,

CI has tested the following submission:
Status:     SUCCESS
Name:       [bpf-next] selftests/bpf: Add a test for mmap-able map in map
Patchwork:  https://patchwork.kernel.org/project/netdevbpf/list/?series=873122&state=*
Matrix:     https://github.com/kernel-patches/bpf/actions/runs/10053209093

No further action is necessary on your part.


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Re: [PATCH bpf-next] selftests/bpf: Add a test for mmap-able map in map

[Martin KaFai Lau]

On 7/22/24 10:14 PM, Song Liu wrote:
> diff --git a/tools/testing/selftests/bpf/progs/mmap_inner_array.c b/tools/testing/selftests/bpf/progs/mmap_inner_array.c
> new file mode 100644
> index 000000000000..db8ca2aa4347
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/progs/mmap_inner_array.c
> @@ -0,0 +1,59 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/* Copyright (c) 2024 Meta Platforms, Inc. and affiliates. */
> +
> +#include "vmlinux.h"
> +#include <bpf/bpf_helpers.h>
> +#include <bpf/bpf_tracing.h>

nit. bpf_tracing.h is not needed.

> +
> +#include "bpf_misc.h"
> +#include "bpf_experimental.h"

Same for bpf_experimental.h. Removed before applying. Thanks.

Re: [PATCH bpf-next] selftests/bpf: Add a test for mmap-able map in map

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to bpf/bpf-next.git (master)
by Martin KaFai Lau <martin.lau@kernel.org>:

On Mon, 22 Jul 2024 22:14:55 -0700 you wrote:
> Regular BPF hash map is not mmap-able from user space. However, map-in-map
> with outer map of type BPF_MAP_TYPE_HASH_OF_MAPS and mmap-able array as
> inner map can perform similar operations as a mmap-able hash map. This
> can be used by applications that benefit from fast accesses to some local
> data.
> 
> Add a selftest to show this use case.
> 
> [...]

Here is the summary with links:
  - [bpf-next] selftests/bpf: Add a test for mmap-able map in map
    https://git.kernel.org/bpf/bpf-next/c/541b135010ce

You are awesome, thank you!
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