selftests/bpf: Fix map_ptr test cases for CPUMAP, HASHMAP

The map_ptr test fails on a 4 vCPU QEMU/armhf system with error E2BIG:

  root@qemu-armhf:/usr/libexec/kselftests-bpf# ./test_progs -a map_ptr
  test_map_ptr:PASS:skel_open 0 nsec
  test_map_ptr:FAIL:skel_load unexpected error: -7 (errno 7)
  torvalds#192     map_ptr:FAIL

This results from trying to create a CPUMAP map with 'max_entries' set to
8, since the kernel limits this to the number of logical CPUs (i.e. 4).
Fix by determining the number of CPUs and setting 'max_entries' from
userspace, similar to the RINGBUF map setup.

The last fix reveals another bug where the HASHMAP subtest hard-codes
the expected htab element size assuming a 64-bit host, which fails on
32-bit armhf because 'struct htab_elem' depends on host word size. As
above, fix this by determining the correct element size and writing the
expected value from userspace. Since the 'struct htab_elem' declaration
is not in uapi, create a local version that captures the same type/size
and alignment variation with system word size. While not ideal, this is
still better than hard-coding a single value.

Signed-off-by: Tony Ambardar <tony.ambardar@gmail.com>

Author: guidosarducci

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

@@ -12,6 +12,21 @@ void test_map_ptr(void)
 	char buf[128];
 	int err;
 	int page_size = getpagesize();
+	int num_cpus = sysconf(_SC_NPROCESSORS_ONLN);
+	/*
+	 * Need to calc size of 'struct htab_elem' since it depends on
+	 * host word size, but it's neither in a header nor can we include
+	 * vmlinux.h here because that fails to compile.  Instead, use a
+	 * simplified version of the struct for 32/64-bit sizing info.
+	 */
+	struct dummy_htab_elem {
+		struct {
+			void* a[4];
+			int b;
+		};
+		int c;
+		char d[] __attribute__((__aligned__(8)));
+	};
 	LIBBPF_OPTS(bpf_test_run_opts, topts,
 		.data_in = &pkt_v4,
 		.data_size_in = sizeof(pkt_v4),
@@ -25,12 +40,19 @@ void test_map_ptr(void)
 		return;
 
 	skel->maps.m_ringbuf.max_entries = page_size;
+	skel->maps.m_cpumap.max_entries = num_cpus;
 
 	err = map_ptr_kern_lskel__load(skel);
 	if (!ASSERT_OK(err, "skel_load"))
 		goto cleanup;
 
 	skel->bss->page_size = page_size;
+	skel->bss->num_cpus = num_cpus;
+	/*
+	 * Determine size of struct htab_elem + key + val, noting the
+	 * kernel rounds up our u32 key and val sizes by 8.
+	 */
+	skel->bss->htab_elem_size = sizeof(struct dummy_htab_elem) + 8 + 8;
 
 	err = bpf_prog_test_run_opts(skel->progs.cg_skb.prog_fd, &topts);
 

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

@@ -12,7 +12,10 @@ _Static_assert(MAX_ENTRIES < LOOP_BOUND, "MAX_ENTRIES must be < LOOP_BOUND");
 
 enum bpf_map_type g_map_type = BPF_MAP_TYPE_UNSPEC;
 __u32 g_line = 0;
-int page_size = 0; /* userspace should set it */
+
+int page_size = 0; /* userspace should set these */
+int num_cpus = 0;
+int htab_elem_size = 0;
 
 #define VERIFY_TYPE(type, func) ({	\
 	g_map_type = type;		\
@@ -114,7 +117,7 @@ static inline int check_hash(void)
 	VERIFY(check_default_noinline(&hash->map, map));
 
 	VERIFY(hash->n_buckets == MAX_ENTRIES);
-	VERIFY(hash->elem_size == 64);
+	VERIFY(hash->elem_size == htab_elem_size);
 
 	VERIFY(hash->count.counter == 0);
 	VERIFY(bpf_map_sum_elem_count(map) == 0);
@@ -463,7 +466,7 @@ static inline int check_cpumap(void)
 	struct bpf_cpu_map *cpumap = (struct bpf_cpu_map *)&m_cpumap;
 	struct bpf_map *map = (struct bpf_map *)&m_cpumap;
 
-	VERIFY(check_default(&cpumap->map, map));
+	VERIFY(check(&cpumap->map, map, sizeof(__u32), sizeof(__u32), num_cpus));
 
 	return 1;
 }