[PATCH bpf-next 14/16] selftests/bpf: Add test for arena percpu-only object

[Xu Kuohai]

From: Xu Kuohai <xukuohai@xxxxxxxxxx>

Add the __arena_percpu macro to bpf_arena_common.h and a test object
with only a arena percpu variable.

Signed-off-by: Xu Kuohai <xukuohai@xxxxxxxxxx>
---
 .../bpf/libarena/include/bpf_arena_common.h   |   2 +
 .../selftests/bpf/prog_tests/arena_percpu.c   | 148 ++++++++++++++++++
 .../selftests/bpf/progs/arena_percpu_only.c   |  21 +++
 3 files changed, 171 insertions(+)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/arena_percpu.c
 create mode 100644 tools/testing/selftests/bpf/progs/arena_percpu_only.c

diff --git a/tools/testing/selftests/bpf/libarena/include/bpf_arena_common.h b/tools/testing/selftests/bpf/libarena/include/bpf_arena_common.h
index 82aafe879fae..7cdee141764e 100644
--- a/tools/testing/selftests/bpf/libarena/include/bpf_arena_common.h
+++ b/tools/testing/selftests/bpf/libarena/include/bpf_arena_common.h
@@ -35,11 +35,13 @@
 #if defined(__BPF_FEATURE_ADDR_SPACE_CAST) && !defined(BPF_ARENA_FORCE_ASM)
 #define __arena __attribute__((address_space(1))) __attribute__((btf_type_tag("arena")))
 #define __arena_global __attribute__((address_space(1)))
+#define __arena_percpu __attribute__((address_space(1))) __attribute__((section(".arena.percpu")))
 #define cast_kern(ptr) /* nop for bpf prog. emitted by LLVM */
 #define cast_user(ptr) /* nop for bpf prog. emitted by LLVM */
 #else
 #define __arena __attribute__((btf_type_tag("arena")))
 #define __arena_global SEC(".addr_space.1")
+#define __arena_percpu SEC(".arena.percpu")
 #define cast_kern(ptr) bpf_addr_space_cast(ptr, 0, 1)
 #define cast_user(ptr) bpf_addr_space_cast(ptr, 1, 0)
 #endif
diff --git a/tools/testing/selftests/bpf/prog_tests/arena_percpu.c b/tools/testing/selftests/bpf/prog_tests/arena_percpu.c
new file mode 100644
index 000000000000..27d4721c7ae9
--- /dev/null
+++ b/tools/testing/selftests/bpf/prog_tests/arena_percpu.c
@@ -0,0 +1,148 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2026 Huawei Technologies Inc. */
+#include <test_progs.h>
+#include <unistd.h>
+#include <sched.h>
+#include <sys/mman.h>
+#include "bpf/libbpf_internal.h"
+#include "arena_percpu_only.skel.h"
+
+static cpu_set_t affinity_save;
+
+static int pin_to(int cpu)
+{
+	cpu_set_t cpuset;
+
+	CPU_ZERO(&cpuset);
+	CPU_SET(cpu, &cpuset);
+	return sched_setaffinity(0, sizeof(cpuset), &cpuset);
+}
+
+static int run_on_cpu(int cpu, struct bpf_program *prog, const char *name)
+{
+	LIBBPF_OPTS(bpf_test_run_opts, opts);
+	int err;
+
+	if (pin_to(cpu))
+		return -1;
+
+	err = bpf_prog_test_run_opts(bpf_program__fd(prog), &opts);
+
+	if (!ASSERT_OK(err, name))
+		return -1;
+	if (!ASSERT_OK(opts.retval, name))
+		return -1;
+	return 0;
+}
+
+static int save_affinity(void)
+{
+	if (!ASSERT_OK(sched_getaffinity(0, sizeof(affinity_save), &affinity_save),
+		       "save_affinity"))
+		return -1;
+	return 0;
+}
+
+static void restore_affinity(void)
+{
+	sched_setaffinity(0, sizeof(affinity_save), &affinity_save);
+}
+
+static int parse_possible_cpus(bool **possible, int *nr_possible)
+{
+	if (!ASSERT_OK(parse_cpu_mask_file("/sys/devices/system/cpu/possible",
+					   possible, nr_possible),
+		       "parse_possible"))
+		return -1;
+	return 0;
+}
+
+/* check one cpu's copy of a per-cpu global */
+static void check_percpu_value(struct bpf_map *arena, void *var, int cpu,
+			       __u64 expected, const char *name)
+{
+	__u64 *p = bpf_map__arena_percpu_ptr(arena, var, cpu);
+
+	if (!ASSERT_OK_PTR(p, name))
+		return;
+	ASSERT_EQ(*p, expected, name);
+}
+
+static void test_arena_percpu_only(void)
+{
+	struct arena_percpu_only *skel;
+	struct bpf_map *arena;
+	bool *possible = NULL;
+	int possible_cpus, cpu, picked_cpu = -1, i, err;
+
+	if (save_affinity())
+		return;
+
+	skel = arena_percpu_only__open();
+	if (!ASSERT_OK_PTR(skel, "open"))
+		return;
+
+	if (parse_possible_cpus(&possible, &possible_cpus))
+		goto out;
+
+	/* size the arena for the per-cpu chunks and load the object */
+	if (!ASSERT_OK(bpf_map__set_max_entries(skel->maps.arena, possible_cpus),
+		       "set_max_entries"))
+		goto out;
+	if (!ASSERT_OK(arena_percpu_only__load(skel), "load"))
+		goto out;
+	arena = skel->maps.arena;
+
+	if (!ASSERT_OK_PTR(skel->arena_percpu, "arena_percpu"))
+		goto out;
+
+	/* every chunk starts as a copy of the initialized section */
+	for (cpu = 0; cpu < possible_cpus; cpu++) {
+		if (!possible[cpu])
+			continue;
+		check_percpu_value(arena, &skel->arena_percpu->counter, cpu,
+				   0x123456, "counter_init");
+	}
+
+	/* pick one cpu to pin */
+	for (i = 0; i < CPU_SETSIZE; i++) {
+		if (CPU_ISSET(i, &affinity_save)) {
+			picked_cpu = i;
+			break;
+		}
+	}
+	if (!ASSERT_GE(picked_cpu, 0, "pick_cpu"))
+		goto out;
+
+	err = run_on_cpu(picked_cpu, skel->progs.arena_percpu_only_write, "run on cpu");
+	if (err < 0)
+		goto out;
+
+	/* only the cpu the program ran on got written */
+	for (cpu = 0; cpu < possible_cpus; cpu++) {
+		if (!possible[cpu])
+			continue;
+
+		if (cpu == picked_cpu)
+			check_percpu_value(arena, &skel->arena_percpu->counter,
+					   cpu, picked_cpu, "counter_written");
+		else
+			check_percpu_value(arena, &skel->arena_percpu->counter,
+					   cpu, 0x123456, "counter_untouched");
+	}
+
+out:
+	free(possible);
+	arena_percpu_only__destroy(skel);
+	restore_affinity();
+}
+
+void test_arena_percpu(void)
+{
+	if (!feat_supported(NULL, FEAT_ARENA_PERCPU_DATA)) {
+		test__skip();
+		return;
+	}
+	if (test__start_subtest("percpu_only"))
+		test_arena_percpu_only();
+}
diff --git a/tools/testing/selftests/bpf/progs/arena_percpu_only.c b/tools/testing/selftests/bpf/progs/arena_percpu_only.c
new file mode 100644
index 000000000000..35e4ff983e65
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/arena_percpu_only.c
@@ -0,0 +1,21 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2026 Huawei Technologies Inc. */
+#include <vmlinux.h>
+#include <bpf/bpf_helpers.h>
+#include "bpf_arena_common.h"
+
+struct {
+	__uint(type, BPF_MAP_TYPE_ARENA);
+	__uint(map_flags, BPF_F_MMAPABLE);
+} arena SEC(".maps");
+
+__u64 __arena_percpu counter = 0x123456;
+
+SEC("syscall")
+int arena_percpu_only_write(void *ctx)
+{
+	counter = bpf_get_smp_processor_id();
+	return 0;
+}
+
+char LICENSE[] SEC("license") = "GPL";
-- 
2.47.3