selftests/mm: configure nr_hugepages for arm64

Arm64 has a default hugepage size of 512MB when CONFIG_ARM64_64K_PAGES=y
is enabled.  While testing on arm64 platforms having up to 4PB of virtual
address space, a minimum of 6 hugepages were required for all test cases
to pass.  Support for this requirement has been added.

Link: https://lkml.kernel.org/r/20230323105243.2807166-5-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/run_vmtests.sh

@@ -236,8 +236,16 @@ if [ $VADDR64 -ne 0 ]; then
 	CATEGORY="hugevm" run_test ./virtual_address_range
 	echo $prev_policy > /proc/sys/vm/overcommit_memory
 
-	# virtual address 128TB switch test
+	# va high address boundary switch test
+	ARCH_ARM64="arm64"
+	prev_nr_hugepages=$(cat /proc/sys/vm/nr_hugepages)
+	if [ "$ARCH" == "$ARCH_ARM64" ]; then
+		echo 6 > /proc/sys/vm/nr_hugepages
+	fi
 	CATEGORY="hugevm" run_test ./va_high_addr_switch.sh
+	if [ "$ARCH" == "$ARCH_ARM64" ]; then
+		echo $prev_nr_hugepages > /proc/sys/vm/nr_hugepages
+	fi
 fi # VADDR64
 
 # vmalloc stability smoke test