Revert "s390/mm: Allow large pages for KASAN shadow mapping"

BugLink: https://bugs.launchpad.net/bugs/2103829

commit cc00550 upstream.

This reverts commit ff123eb.

Allowing large pages for KASAN shadow mappings isn't inherently wrong,
but adding POPULATE_KASAN_MAP_SHADOW to large_allowed() exposes an issue
in can_large_pud() and can_large_pmd().

Since commit d8073dc ("s390/mm: Allow large pages only for aligned
physical addresses"), both can_large_pud() and can_large_pmd() call _pa()
to check if large page physical addresses are aligned. However, _pa()
has a side effect: it allocates memory in POPULATE_KASAN_MAP_SHADOW
mode. This results in massive memory leaks.

The proper fix would be to address both large_allowed() and _pa()'s side
effects, but for now, revert this change to avoid the leaks.

Fixes: ff123eb ("s390/mm: Allow large pages for KASAN shadow mapping")
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Noah Wager <noah.wager@canonical.com>
Signed-off-by: Mehmet Basaran <mehmet.basaran@canonical.com>

Author: Vasily Gorbik

arch/s390/boot/vmem.c

@@ -264,17 +264,7 @@ static unsigned long _pa(unsigned long addr, unsigned long size, enum populate_m
 
 static bool large_allowed(enum populate_mode mode)
 {
-	switch (mode) {
-	case POPULATE_DIRECT:
-	case POPULATE_IDENTITY:
-	case POPULATE_KERNEL:
-#ifdef CONFIG_KASAN
-	case POPULATE_KASAN_MAP_SHADOW:
-#endif
-		return true;
-	default:
-		return false;
-	}
+	return (mode == POPULATE_DIRECT) || (mode == POPULATE_IDENTITY) || (mode == POPULATE_KERNEL);
 }
 
 static bool can_large_pud(pud_t *pu_dir, unsigned long addr, unsigned long end,