selftests/mm: add platform independent in code comments

The in code comments for the selftest were made on the basis of 128TB
switch, an architecture feature specific to PowerPc and x86 platforms. 
Keeping in mind the support added for arm64 platforms which implements a
256TB switch, a more generic explanation has been provided.

Link: https://lkml.kernel.org/r/20230323105243.2807166-4-chaitanyas.prakash@arm.comSigned-off-by: Chaitanya S Prakash <chaitanyas.prakash@arm.com>
Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

tools/testing/selftests/mm/va_high_addr_switch.c

@@ -30,8 +30,8 @@
 #endif
 
 /*
- * >= 128TB is the hint addr value we used to select
- * large address space.
+ * The hint addr value is used to allocate addresses
+ * beyond the high address switch boundary.
  */
 
 #define ADDR_MARK_128TB	(1UL << 47)
@@ -73,9 +73,10 @@ static struct testcase testcases[] = {
 	},
 	{
 		/*
-		 * We should never allocate at the requested address or above it
-		 * The len cross the 128TB boundary. Without MAP_FIXED
-		 * we will always search in the lower address space.
+		 * Unless MAP_FIXED is specified, allocation based on hint
+		 * addr is never at requested address or above it, which is
+		 * beyond high address switch boundary in this case. Instead,
+		 * a suitable allocation is found in lower address space.
 		 */
 		.addr = ((void *)(ADDR_SWITCH_HINT - PAGE_SIZE)),
 		.size = 2 * PAGE_SIZE,
@@ -85,8 +86,8 @@ static struct testcase testcases[] = {
 	},
 	{
 		/*
-		 * Exact mapping at 128TB, the area is free we should get that
-		 * even without MAP_FIXED.
+		 * Exact mapping at high address switch boundary, should
+		 * be obtained even without MAP_FIXED as area is free.
 		 */
 		.addr = ((void *)(ADDR_SWITCH_HINT)),
 		.size = PAGE_SIZE,