selftests/bpf: extend existing map resize tests for per-cpu use case

Add a per-cpu array resizing use case and demonstrate how
bpf_get_smp_processor_id() can be used to directly access proper data
with no extra checks.
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/r/20230711232400.1658562-2-andrii@kernel.orgSigned-off-by: Alexei Starovoitov <ast@kernel.org>

tools/testing/selftests/bpf/prog_tests/global_map_resize.c

@@ -22,7 +22,7 @@ static void global_map_resize_bss_subtest(void)
 	struct test_global_map_resize *skel;
 	struct bpf_map *map;
 	const __u32 desired_sz = sizeof(skel->bss->sum) + sysconf(_SC_PAGE_SIZE) * 2;
-	size_t array_len, actual_sz;
+	size_t array_len, actual_sz, new_sz;
 
 	skel = test_global_map_resize__open();
 	if (!ASSERT_OK_PTR(skel, "test_global_map_resize__open"))
@@ -42,6 +42,10 @@ static void global_map_resize_bss_subtest(void)
 	if (!ASSERT_EQ(bpf_map__value_size(map), desired_sz, "resize"))
 		goto teardown;
 
+	new_sz = sizeof(skel->data_percpu_arr->percpu_arr[0]) * libbpf_num_possible_cpus();
+	err = bpf_map__set_value_size(skel->maps.data_percpu_arr, new_sz);
+	ASSERT_OK(err, "percpu_arr_resize");
+
 	/* set the expected number of elements based on the resized array */
 	array_len = (desired_sz - sizeof(skel->bss->sum)) / sizeof(skel->bss->array[0]);
 	if (!ASSERT_GT(array_len, 1, "array_len"))
@@ -84,11 +88,11 @@ static void global_map_resize_bss_subtest(void)
 
 static void global_map_resize_data_subtest(void)
 {
-	int err;
 	struct test_global_map_resize *skel;
 	struct bpf_map *map;
 	const __u32 desired_sz = sysconf(_SC_PAGE_SIZE) * 2;
-	size_t array_len, actual_sz;
+	size_t array_len, actual_sz, new_sz;
+	int err;
 
 	skel = test_global_map_resize__open();
 	if (!ASSERT_OK_PTR(skel, "test_global_map_resize__open"))
@@ -108,6 +112,10 @@ static void global_map_resize_data_subtest(void)
 	if (!ASSERT_EQ(bpf_map__value_size(map), desired_sz, "resize"))
 		goto teardown;
 
+	new_sz = sizeof(skel->data_percpu_arr->percpu_arr[0]) * libbpf_num_possible_cpus();
+	err = bpf_map__set_value_size(skel->maps.data_percpu_arr, new_sz);
+	ASSERT_OK(err, "percpu_arr_resize");
+
 	/* set the expected number of elements based on the resized array */
 	array_len = (desired_sz - sizeof(skel->bss->sum)) / sizeof(skel->data_custom->my_array[0]);
 	if (!ASSERT_GT(array_len, 1, "array_len"))

tools/testing/selftests/bpf/progs/test_global_map_resize.c

@@ -29,13 +29,16 @@ int my_int SEC(".data.non_array");
 int my_array_first[1] SEC(".data.array_not_last");
 int my_int_last SEC(".data.array_not_last");
 
+int percpu_arr[1] SEC(".data.percpu_arr");
+
 SEC("tp/syscalls/sys_enter_getpid")
 int bss_array_sum(void *ctx)
 {
 	if (pid != (bpf_get_current_pid_tgid() >> 32))
 		return 0;
 
-	sum = 0;
+	/* this will be zero, we just rely on verifier not rejecting this */
+	sum = percpu_arr[bpf_get_smp_processor_id()];
 
 	for (size_t i = 0; i < bss_array_len; ++i)
 		sum += array[i];
@@ -49,7 +52,8 @@ int data_array_sum(void *ctx)
 	if (pid != (bpf_get_current_pid_tgid() >> 32))
 		return 0;
 
-	sum = 0;
+	/* this will be zero, we just rely on verifier not rejecting this */
+	sum = percpu_arr[bpf_get_smp_processor_id()];
 
 	for (size_t i = 0; i < data_array_len; ++i)
 		sum += my_array[i];