mm: replace get_user_pages_remote() write/force parameters with gup_flags

This removes the 'write' and 'force' from get_user_pages_remote() and
replaces them with 'gup_flags' to make the use of FOLL_FORCE explicit in
callers as use of this flag can result in surprising behaviour (and
hence bugs) within the mm subsystem.

Signed-off-by: Lorenzo Stoakes <lstoakes@gmail.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/gup.c

@@ -915,9 +915,7 @@ EXPORT_SYMBOL(get_user_pages_unlocked);
  * @mm:		mm_struct of target mm
  * @start:	starting user address
  * @nr_pages:	number of pages from start to pin
- * @write:	whether pages will be written to by the caller
- * @force:	whether to force access even when user mapping is currently
- *		protected (but never forces write access to shared mapping).
+ * @gup_flags:	flags modifying lookup behaviour
  * @pages:	array that receives pointers to the pages pinned.
  *		Should be at least nr_pages long. Or NULL, if caller
  *		only intends to ensure the pages are faulted in.
@@ -946,9 +944,9 @@ EXPORT_SYMBOL(get_user_pages_unlocked);
  * or similar operation cannot guarantee anything stronger anyway because
  * locks can't be held over the syscall boundary.
  *
- * If write=0, the page must not be written to. If the page is written to,
- * set_page_dirty (or set_page_dirty_lock, as appropriate) must be called
- * after the page is finished with, and before put_page is called.
+ * If gup_flags & FOLL_WRITE == 0, the page must not be written to. If the page
+ * is written to, set_page_dirty (or set_page_dirty_lock, as appropriate) must
+ * be called after the page is finished with, and before put_page is called.
  *
  * get_user_pages is typically used for fewer-copy IO operations, to get a
  * handle on the memory by some means other than accesses via the user virtual
@@ -965,18 +963,12 @@ EXPORT_SYMBOL(get_user_pages_unlocked);
  */
 long get_user_pages_remote(struct task_struct *tsk, struct mm_struct *mm,
 		unsigned long start, unsigned long nr_pages,
-		int write, int force, struct page **pages,
+		unsigned int gup_flags, struct page **pages,
 		struct vm_area_struct **vmas)
 {
-	unsigned int flags = FOLL_TOUCH | FOLL_REMOTE;
-
-	if (write)
-		flags |= FOLL_WRITE;
-	if (force)
-		flags |= FOLL_FORCE;
-
 	return __get_user_pages_locked(tsk, mm, start, nr_pages, pages, vmas,
-				       NULL, false, flags);
+				       NULL, false,
+				       gup_flags | FOLL_TOUCH | FOLL_REMOTE);
 }
 EXPORT_SYMBOL(get_user_pages_remote);