selftests/mm: skip test for non-LPA2 and non-LVA systems

Post my improvement of the test in e4a4ba415419 ("selftests/mm:
va_high_addr_switch: dynamically initialize testcases to enable LPA2
testing"):

The test begins to fail on 4k and 16k pages, on non-LPA2 systems. To
reduce noise in the CI systems, let us skip the test when higher address
space is not implemented.

Link: https://lkml.kernel.org/r/[e-mail]
Fixes: e4a4ba415419 ("selftests/mm: va_high_addr_switch: dynamically initialize testcases to enable LPA2 testing")
Signed-off-by: Dev Jain <[e-mail]>
Reviewed-by: Ryan Roberts <[e-mail]>
Cc: Anshuman Khandual <[e-mail]>
Cc: Mark Brown <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>

tools/testing/selftests/mm/va_high_addr_switch.c

···
 	return ret;
 }
 
+#ifdef __aarch64__
+/* Check if userspace VA > 48 bits */
+static int high_address_present(void)
+{
+	void *ptr = mmap((void *)(1UL << 50), 1, PROT_READ | PROT_WRITE,
+			 MAP_PRIVATE | MAP_ANONYMOUS | MAP_FIXED, -1, 0);
+	if (ptr == MAP_FAILED)
+		return 0;
+
+	munmap(ptr, 1);
+	return 1;
+}
+#endif
+
 static int supported_arch(void)
 {
 #if defined(__powerpc64__)
···
 #elif defined(__x86_64__)
 	return 1;
 #elif defined(__aarch64__)
-	return 1;
+	return high_address_present();
 #else
 	return 0;
 #endif