selftests/bpf: Increase xdp data size for arm64 64K page size

With arm64 64K page size, the following 4 subtests failed:
  #97/25   dynptr/test_probe_read_user_dynptr:FAIL
  #97/26   dynptr/test_probe_read_kernel_dynptr:FAIL
  #97/27   dynptr/test_probe_read_user_str_dynptr:FAIL
  #97/28   dynptr/test_probe_read_kernel_str_dynptr:FAIL

These failures are due to function bpf_dynptr_check_off_len() in
include/linux/bpf.h where there is a test
  if (len > size || offset > size - len)
    return -E2BIG;
With 64K page size, the 'offset' is greater than 'size - len',
which caused the test failure.

For 64KB page size, this patch increased the xdp buffer size from 5000 to
90000. The above 4 test failures are fixed as 'size' value is increased.
But it introduced two new failures:
  #97/4    dynptr/test_dynptr_copy_xdp:FAIL
  #97/12   dynptr/test_dynptr_memset_xdp_chunks:FAIL

These two failures will be addressed in subsequent patches.

Signed-off-by: Yonghong Song <yonghong.song@linux.dev>
Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>
Acked-by: Mykyta Yatsenko <yatsenko@meta.com>
Link: https://patch.msgid.link/20250725043430.208469-1-yonghong.song@linux.dev

Author: Yonghong Song

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

@@ -51,6 +51,8 @@ static struct {
 	{"test_copy_from_user_task_str_dynptr", SETUP_SYSCALL_SLEEP},
 };
 
+#define PAGE_SIZE_64K 65536
+
 static void verify_success(const char *prog_name, enum test_setup_type setup_type)
 {
 	char user_data[384] = {[0 ... 382] = 'a', '\0'};
@@ -146,14 +148,18 @@ static void verify_success(const char *prog_name, enum test_setup_type setup_typ
 	}
 	case SETUP_XDP_PROG:
 	{
-		char data[5000];
+		char data[90000];
 		int err, prog_fd;
 		LIBBPF_OPTS(bpf_test_run_opts, opts,
 			    .data_in = &data,
-			    .data_size_in = sizeof(data),
 			    .repeat = 1,
 		);
 
+		if (getpagesize() == PAGE_SIZE_64K)
+			opts.data_size_in = sizeof(data);
+		else
+			opts.data_size_in = 5000;
+
 		prog_fd = bpf_program__fd(prog);
 		err = bpf_prog_test_run_opts(prog_fd, &opts);