mm: replace __access_remote_vm() write parameter with gup_flags

This removes the 'write' argument from __access_remote_vm() and replaces
it with 'gup_flags' as use of this function previously silently implied
FOLL_FORCE, whereas after this patch callers explicitly pass this flag.

We make this explicit as use of FOLL_FORCE 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>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/nommu.c

@@ -1809,9 +1809,10 @@ void filemap_map_pages(struct fault_env *fe,
 EXPORT_SYMBOL(filemap_map_pages);
 
 static int __access_remote_vm(struct task_struct *tsk, struct mm_struct *mm,
-		unsigned long addr, void *buf, int len, int write)
+		unsigned long addr, void *buf, int len, unsigned int gup_flags)
 {
 	struct vm_area_struct *vma;
+	int write = gup_flags & FOLL_WRITE;
 
 	down_read(&mm->mmap_sem);
 
@@ -1853,7 +1854,8 @@ static int __access_remote_vm(struct task_struct *tsk, struct mm_struct *mm,
 int access_remote_vm(struct mm_struct *mm, unsigned long addr,
 		void *buf, int len, int write)
 {
-	return __access_remote_vm(NULL, mm, addr, buf, len, write);
+	return __access_remote_vm(NULL, mm, addr, buf, len,
+			write ? FOLL_WRITE : 0);
 }
 
 /*
@@ -1871,7 +1873,8 @@ int access_process_vm(struct task_struct *tsk, unsigned long addr, void *buf, in
 	if (!mm)
 		return 0;
 
-	len = __access_remote_vm(tsk, mm, addr, buf, len, write);
+	len = __access_remote_vm(tsk, mm, addr, buf, len,
+			write ? FOLL_WRITE : 0);
 
 	mmput(mm);
 	return len;