mm: remove write/force parameters from __get_user_pages_unlocked()

This removes the redundant 'write' and 'force' parameters from
__get_user_pages_unlocked() 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: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Acked-by: Michal Hocko <mhocko@suse.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/gup.c

@@ -875,17 +875,11 @@ EXPORT_SYMBOL(get_user_pages_locked);
  */
 __always_inline long __get_user_pages_unlocked(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, unsigned int gup_flags)
 {
 	long ret;
 	int locked = 1;
 
-	if (write)
-		gup_flags |= FOLL_WRITE;
-	if (force)
-		gup_flags |= FOLL_FORCE;
-
 	down_read(&mm->mmap_sem);
 	ret = __get_user_pages_locked(tsk, mm, start, nr_pages, pages, NULL,
 				      &locked, false, gup_flags);
@@ -915,8 +909,15 @@ EXPORT_SYMBOL(__get_user_pages_unlocked);
 long get_user_pages_unlocked(unsigned long start, unsigned long nr_pages,
 			     int write, int force, struct page **pages)
 {
+	unsigned int flags = FOLL_TOUCH;
+
+	if (write)
+		flags |= FOLL_WRITE;
+	if (force)
+		flags |= FOLL_FORCE;
+
 	return __get_user_pages_unlocked(current, current->mm, start, nr_pages,
-					 write, force, pages, FOLL_TOUCH);
+					 pages, flags);
 }
 EXPORT_SYMBOL(get_user_pages_unlocked);
 

mm/nommu.c

@@ -185,8 +185,7 @@ EXPORT_SYMBOL(get_user_pages_locked);
 
 long __get_user_pages_unlocked(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, unsigned int gup_flags)
 {
 	long ret;
 	down_read(&mm->mmap_sem);
@@ -200,8 +199,15 @@ EXPORT_SYMBOL(__get_user_pages_unlocked);
 long get_user_pages_unlocked(unsigned long start, unsigned long nr_pages,
 			     int write, int force, struct page **pages)
 {
+	unsigned int flags = 0;
+
+	if (write)
+		flags |= FOLL_WRITE;
+	if (force)
+		flags |= FOLL_FORCE;
+
 	return __get_user_pages_unlocked(current, current->mm, start, nr_pages,
-					 write, force, pages, 0);
+					 pages, flags);
 }
 EXPORT_SYMBOL(get_user_pages_unlocked);
 

mm/process_vm_access.c

@@ -88,12 +88,16 @@ static int process_vm_rw_single_vec(unsigned long addr,
 	ssize_t rc = 0;
 	unsigned long max_pages_per_loop = PVM_MAX_KMALLOC_PAGES
 		/ sizeof(struct pages *);
+	unsigned int flags = FOLL_REMOTE;
 
 	/* Work out address and page range required */
 	if (len == 0)
 		return 0;
 	nr_pages = (addr + len - 1) / PAGE_SIZE - addr / PAGE_SIZE + 1;
 
+	if (vm_write)
+		flags |= FOLL_WRITE;
+
 	while (!rc && nr_pages && iov_iter_count(iter)) {
 		int pages = min(nr_pages, max_pages_per_loop);
 		size_t bytes;
@@ -104,8 +108,7 @@ static int process_vm_rw_single_vec(unsigned long addr,
 		 * current/current->mm
 		 */
 		pages = __get_user_pages_unlocked(task, mm, pa, pages,
-						  vm_write, 0, process_pages,
-						  FOLL_REMOTE);
+						  process_pages, flags);
 		if (pages <= 0)
 			return -EFAULT;