[patch 09/12] mm/mapping_dirty_helpers: guard hugepage pud's usage

[Andrew Morton <akpm@linux-foundation.org>]

From: Zack Rusin <zackr@vmware.com>
Subject: mm/mapping_dirty_helpers: guard hugepage pud's usage

Mapping dirty helpers have, so far, been only used on X86, but a port of
vmwgfx to ARM64 exposed a problem which results in a compilation error on
ARM64 systems:

mm/mapping_dirty_helpers.c: In function `wp_clean_pud_entry':
mm/mapping_dirty_helpers.c:172:32: error: implicit declaration of function `pud_dirty'; did you mean `pmd_dirty'? [-Werror=implicit-function-declaration]

This is due to the fact that mapping_dirty_helpers code assumes that
pud_dirty is always defined, which is not the case for architectures that
don't define CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD.

ARM64 arch is a little inconsistent when it comes to PUD hugepage helpers,
e.g.  it defines pud_young but not pud_dirty but regardless of that the
core kernel code shouldn't assume that any of the PUD hugepage helpers are
available unless CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD is defined. 
This prevents compilation errors whenever one of the drivers is ported to
new architectures.

Link: https://lkml.kernel.org/r/20210409165151.694574-1-zackr@vmware.com
Signed-off-by: Zack Rusin <zackr@vmware.com>
Reviewed-by: Thomas Hellstrm (Intel) <thomas_os@shipmail.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/mapping_dirty_helpers.c |    2 ++
 1 file changed, 2 insertions(+)

--- a/mm/mapping_dirty_helpers.c~mm-mapping_dirty_helpers-guard-hugepage-puds-usage
+++ a/mm/mapping_dirty_helpers.c
@@ -165,10 +165,12 @@ static int wp_clean_pud_entry(pud_t *pud
 		return 0;
 	}
 
+#ifdef CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD
 	/* Huge pud */
 	walk->action = ACTION_CONTINUE;
 	if (pud_trans_huge(pudval) || pud_devmap(pudval))
 		WARN_ON(pud_write(pudval) || pud_dirty(pudval));
+#endif
 
 	return 0;
 }
_