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

BugLink: https://bugs.launchpad.net/bugs/1811080

commit 3b913179 upstream.

This removes the 'write' and 'force' use from get_user_pages_locked()
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>
[bwh: Backported to 4.4: adjust context]
Signed-off-by: Ben Hutchings <ben.hutchings@codethink.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Juerg Haefliger <juergh@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>

include/linux/mm.h

@@ -1225,8 +1225,7 @@ long get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
 		    struct vm_area_struct **vmas);
 long get_user_pages_locked(struct task_struct *tsk, struct mm_struct *mm,
 		    unsigned long start, unsigned long nr_pages,
-		    int write, int force, struct page **pages,
-		    int *locked);
+		    unsigned int gup_flags, struct page **pages, int *locked);
 long __get_user_pages_unlocked(struct task_struct *tsk, struct mm_struct *mm,
 			       unsigned long start, unsigned long nr_pages,
 			       struct page **pages, unsigned int gup_flags);

mm/frame_vector.c

@@ -41,10 +41,16 @@ int get_vaddr_frames(unsigned long start, unsigned int nr_frames,
 	int ret = 0;
 	int err;
 	int locked;
+	unsigned int gup_flags = 0;
 
 	if (nr_frames == 0)
 		return 0;
 
+	if (write)
+		gup_flags |= FOLL_WRITE;
+	if (force)
+		gup_flags |= FOLL_FORCE;
+
 	if (WARN_ON_ONCE(nr_frames > vec->nr_allocated))
 		nr_frames = vec->nr_allocated;
 
@@ -59,7 +65,7 @@ int get_vaddr_frames(unsigned long start, unsigned int nr_frames,
 		vec->got_ref = true;
 		vec->is_pfns = false;
 		ret = get_user_pages_locked(current, mm, start, nr_frames,
-			write, force, (struct page **)(vec->ptrs), &locked);
+			gup_flags, (struct page **)(vec->ptrs), &locked);
 		goto out;
 	}
 

mm/gup.c

@@ -737,18 +737,12 @@ static __always_inline long __get_user_pages_locked(struct task_struct *tsk,
  */
 long get_user_pages_locked(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,
 			   int *locked)
 {
-	unsigned int flags = FOLL_TOUCH;
-
-	if (write)
-		flags |= FOLL_WRITE;
-	if (force)
-		flags |= FOLL_FORCE;
-
 	return __get_user_pages_locked(tsk, mm, start, nr_pages,
-				       pages, NULL, locked, true, flags);
+				       pages, NULL, locked, true,
+				       gup_flags | FOLL_TOUCH);
 }
 EXPORT_SYMBOL(get_user_pages_locked);
 

mm/nommu.c

@@ -201,9 +201,12 @@ EXPORT_SYMBOL(get_user_pages);
 
 long get_user_pages_locked(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,
 			   int *locked)
 {
+	int write = gup_flags & FOLL_WRITE;
+	int force = gup_flags & FOLL_FORCE;
+
 	return get_user_pages(tsk, mm, start, nr_pages, write, force,
 			      pages, NULL);
 }