[PATCH bpf-next v2 5/5] selftests/bpf: Add tests to verify no unintended eviction when updating lru_[percpu_,]hash maps

[Leon Hwang <leon.hwang@linux.dev>]

Add four tests to verify that updating an existing element in LRU hash
maps does not cause unintended eviction of other elements.

The test creates lru_hash/lru_percpu_hash maps with max_entries slots and
populates all of them. It then updates an existing key and verifies that:
1. The update succeeds without error
2. The updated key has the new value
3. All other keys still exist with their original values

This validates the fix that prevents unnecessary LRU eviction when
updating existing elements in full LRU hash maps.

Signed-off-by: Leon Hwang <leon.hwang@linux.dev>
---
 .../selftests/bpf/prog_tests/htab_update.c    | 129 ++++++++++++++++++
 1 file changed, 129 insertions(+)

diff --git a/tools/testing/selftests/bpf/prog_tests/htab_update.c b/tools/testing/selftests/bpf/prog_tests/htab_update.c
index d0b405eb2966..a0c93aae2b99 100644
--- a/tools/testing/selftests/bpf/prog_tests/htab_update.c
+++ b/tools/testing/selftests/bpf/prog_tests/htab_update.c
@@ -143,3 +143,132 @@ void test_htab_update(void)
 	if (test__start_subtest("concurrent_update"))
 		test_concurrent_update();
 }
+
+static void __setaffinity(cpu_set_t *cpus, int cpu)
+{
+	CPU_ZERO(cpus);
+	CPU_SET(cpu, cpus);
+	pthread_setaffinity_np(pthread_self(), sizeof(*cpus), cpus);
+}
+
+static void test_lru_hash_map_update_elem(enum bpf_map_type map_type, u64 map_flags)
+{
+	bool percpu = map_type == BPF_MAP_TYPE_LRU_PERCPU_HASH;
+	int err, map_fd, i, key, nr_cpus, max_entries = 128;
+	u64 *values, value = 0xDEADC0DE;
+	cpu_set_t cpus;
+	LIBBPF_OPTS(bpf_map_create_opts, opts,
+		    .map_flags = map_flags,
+	);
+
+	nr_cpus = libbpf_num_possible_cpus();
+	if (!ASSERT_GT(nr_cpus, 0, "libbpf_num_possible_cpus"))
+		return;
+
+	values = calloc(nr_cpus, sizeof(u64));
+	if (!ASSERT_OK_PTR(values, "calloc values"))
+		return;
+	for (i = 0; i < nr_cpus; i++)
+		values[i] = value;
+
+	map_fd = bpf_map_create(map_type, "test_lru", sizeof(int), sizeof(u64), max_entries, &opts);
+	if (!ASSERT_GE(map_fd, 0, "bpf_map_create")) {
+		free(values);
+		return;
+	}
+
+	/* populate all slots */
+	for (key = 0; key < max_entries; key++) {
+		__setaffinity(&cpus, key%nr_cpus);
+		err = bpf_map_update_elem(map_fd, &key, values, 0);
+		if (!ASSERT_OK(err, "bpf_map_update_elem"))
+			goto out;
+	}
+
+	/* LRU eviction should not happen */
+
+#define CHECK_OTHER_CPUS_VALUES(__val)							\
+	do {										\
+		if (!percpu)								\
+			break;								\
+		for (i = 1; i < nr_cpus; i++)						\
+			if (!ASSERT_EQ(values[i], __val, "bpf_map_lookup_elem value"))	\
+				goto out;						\
+	} while (0)
+
+	__setaffinity(&cpus, 0);
+	key = 0;
+	memset(values, 0, nr_cpus * sizeof(u64));
+	err = bpf_map_update_elem(map_fd, &key, values, 0);
+	if (!ASSERT_OK(err, "bpf_map_update_elem"))
+		goto out;
+
+	err = bpf_map_lookup_elem(map_fd, &key, values);
+	if (!ASSERT_OK(err, "bpf_map_lookup_elem"))
+		goto out;
+	if (!ASSERT_EQ(*values, 0, "bpf_map_lookup_elem value"))
+		goto out;
+	CHECK_OTHER_CPUS_VALUES(0);
+
+	for (key = 1; key < max_entries; key++) {
+		err = bpf_map_lookup_elem(map_fd, &key, values);
+		if (!ASSERT_OK(err, "bpf_map_lookup_elem"))
+			goto out;
+		if (!ASSERT_EQ(*values, value, "bpf_map_lookup_elem value"))
+			goto out;
+		CHECK_OTHER_CPUS_VALUES(value);
+	}
+
+	for (i = 0; i < nr_cpus; i++)
+		values[i] = value;
+
+	key = max_entries;
+	err = bpf_map_update_elem(map_fd, &key, values, 0);
+	if (!ASSERT_OK(err, "bpf_map_update_elem"))
+		goto out;
+
+	err = bpf_map_lookup_elem(map_fd, &key, values);
+	if (!ASSERT_OK(err, "bpf_map_lookup_elem"))
+		goto out;
+	if (!ASSERT_EQ(*values, value, "bpf_map_lookup_elem value"))
+		goto out;
+	CHECK_OTHER_CPUS_VALUES(value);
+
+#undef CHECK_OTHER_CPUS_VALUES
+
+out:
+	close(map_fd);
+	free(values);
+}
+
+static void test_update_lru_hash_map_common_lru(void)
+{
+	test_lru_hash_map_update_elem(BPF_MAP_TYPE_LRU_HASH, 0);
+}
+
+static void test_update_lru_hash_map_percpu_lru(void)
+{
+	test_lru_hash_map_update_elem(BPF_MAP_TYPE_LRU_HASH, BPF_F_NO_COMMON_LRU);
+}
+
+static void test_update_lru_percpu_hash_map_common_lru(void)
+{
+	test_lru_hash_map_update_elem(BPF_MAP_TYPE_LRU_PERCPU_HASH, 0);
+}
+
+static void test_update_lru_percpu_hash_map_percpu_lru(void)
+{
+	test_lru_hash_map_update_elem(BPF_MAP_TYPE_LRU_PERCPU_HASH, BPF_F_NO_COMMON_LRU);
+}
+
+void test_update_lru_hash_maps(void)
+{
+	if (test__start_subtest("lru_hash/common_lru"))
+		test_update_lru_hash_map_common_lru();
+	if (test__start_subtest("lru_hash/percpu_lru"))
+		test_update_lru_hash_map_percpu_lru();
+	if (test__start_subtest("lru_percpu_hash/common_lru"))
+		test_update_lru_percpu_hash_map_common_lru();
+	if (test__start_subtest("lru_percpu_hash/percpu_lru"))
+		test_update_lru_percpu_hash_map_percpu_lru();
+}
-- 
2.52.0