s390/kasan: add option for 4-level paging support

By default 3-level paging is used when the kernel is compiled with
kasan support. Add 4-level paging option to support systems with more
then 3TB of physical memory and to cover 4-level paging specific code
with kasan as well.

Reviewed-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
diff --git a/lib/Kconfig.kasan b/lib/Kconfig.kasan
index befb127..d0bad1b 100644
--- a/lib/Kconfig.kasan
+++ b/lib/Kconfig.kasan
@@ -57,6 +57,15 @@
 
 endchoice
 
+config KASAN_S390_4_LEVEL_PAGING
+	bool "KASan: use 4-level paging"
+	depends on KASAN && S390
+	help
+	  Compiling the kernel with KASan disables automatic 3-level vs
+	  4-level paging selection. 3-level paging is used by default (up
+	  to 3TB of RAM with KASan enabled). This options allows to force
+	  4-level paging instead.
+
 config TEST_KASAN
 	tristate "Module for testing kasan for bug detection"
 	depends on m && KASAN