selftests/bpf: Use value with enough-size when updating per-cpu map

When updating per-cpu map in map_percpu_stats test, patch_map_thread()
only passes 4-bytes-sized value to bpf_map_update_elem(). The expected
size of the value is 8 * num_possible_cpus(), so fix it by passing a
value with enough-size for per-cpu map update.

Signed-off-by: Hou Tao <houtao1@huawei.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20231101032455.3808547-2-houtao@huaweicloud.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

tools/testing/selftests/bpf/map_tests/map_percpu_stats.c

@@ -131,6 +131,12 @@ static bool is_lru(__u32 map_type)
 	       map_type == BPF_MAP_TYPE_LRU_PERCPU_HASH;
 }
 
+static bool is_percpu(__u32 map_type)
+{
+	return map_type == BPF_MAP_TYPE_PERCPU_HASH ||
+	       map_type == BPF_MAP_TYPE_LRU_PERCPU_HASH;
+}
+
 struct upsert_opts {
 	__u32 map_type;
 	int map_fd;
@@ -150,17 +156,26 @@ static int create_small_hash(void)
 
 static void *patch_map_thread(void *arg)
 {
+	/* 8KB is enough for 1024 CPUs. And it is shared between N_THREADS. */
+	static __u8 blob[8 << 10];
 	struct upsert_opts *opts = arg;
+	void *val_ptr;
 	int val;
 	int ret;
 	int i;
 
 	for (i = 0; i < opts->n; i++) {
-		if (opts->map_type == BPF_MAP_TYPE_HASH_OF_MAPS)
+		if (opts->map_type == BPF_MAP_TYPE_HASH_OF_MAPS) {
 			val = create_small_hash();
-		else
+			val_ptr = &val;
+		} else if (is_percpu(opts->map_type)) {
+			val_ptr = blob;
+		} else {
 			val = rand();
-		ret = bpf_map_update_elem(opts->map_fd, &i, &val, 0);
+			val_ptr = &val;
+		}
+
+		ret = bpf_map_update_elem(opts->map_fd, &i, val_ptr, 0);
 		CHECK(ret < 0, "bpf_map_update_elem", "key=%d error: %s\n", i, strerror(errno));
 
 		if (opts->map_type == BPF_MAP_TYPE_HASH_OF_MAPS)