mm: gup: enable FOLL_MM_SYNC by default for FOLL_LONGTERM Drivers that for whatever reason can risk to lose coherency with the MM after taking readonly long term pins (as result of later COW faults), can specify __FOLL_LONGTERM to opt-out from FOLL_MM_SYNC. Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 46ce49b..95eb99e 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h

@@ -2873,13 +2873,15 @@ struct page *follow_page(struct vm_area_struct *vma, unsigned long address,
 #define FOLL_REMOTE	0x2000	/* we are working on non-current tsk/mm */
 #define FOLL_COW	0x4000	/* internal GUP flag */
 #define FOLL_ANON	0x8000	/* don't do file mappings */
-#define FOLL_LONGTERM	0x10000	/* mapping lifetime is indefinite: see below */
+#define __FOLL_LONGTERM	0x10000	/* mapping lifetime is indefinite: see below */
 #define FOLL_SPLIT_PMD	0x20000	/* split huge pmd before returning */
 #define FOLL_PIN	0x40000	/* pages must be released via unpin_user_page */
 #define FOLL_FAST_ONLY	0x80000	/* gup_fast: prevent fall-back to slow gup */
 #define FOLL_NOUNSHARE	0x100000 /* gup: don't trigger a COR fault */
 #define FOLL_MM_SYNC	0x200000/* gup: long term mm coherency to page pins */
 
+#define FOLL_LONGTERM (FOLL_MM_SYNC|__FOLL_LONGTERM)
+
 /*
  * FOLL_PIN and FOLL_LONGTERM may be used in various combinations with each
  * other. Here is what they mean, and how to use them: