mm: remove write/force parameters from __get_user_pages_unlocked()

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

commit d4944b0e upstream.

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>
[bwh: Backported to 4.4:
 - Defer changes in process_vm_rw_single_vec() and async_pf_execute() since
   they use get_user_pages_unlocked() here
 - 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

@@ -1229,8 +1229,7 @@ long get_user_pages_locked(struct task_struct *tsk, struct mm_struct *mm,
 		    int *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 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);

mm/gup.c

@@ -764,17 +764,11 @@ 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);
@@ -805,8 +799,15 @@ 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)
 {
-	return __get_user_pages_unlocked(tsk, mm, start, nr_pages, write,
-					 force, pages, FOLL_TOUCH);
+	unsigned int flags = FOLL_TOUCH;
+
+	if (write)
+		flags |= FOLL_WRITE;
+	if (force)
+		flags |= FOLL_FORCE;
+
+	return __get_user_pages_unlocked(tsk, mm, start, nr_pages,
+					 pages, flags);
 }
 EXPORT_SYMBOL(get_user_pages_unlocked);
 

mm/nommu.c

@@ -211,8 +211,7 @@ 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);
@@ -227,8 +226,15 @@ 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)
 {
-	return __get_user_pages_unlocked(tsk, mm, start, nr_pages, write,
-					 force, pages, 0);
+	unsigned int flags = 0;
+
+	if (write)
+		flags |= FOLL_WRITE;
+	if (force)
+		flags |= FOLL_FORCE;
+
+	return __get_user_pages_unlocked(tsk, mm, start, nr_pages,
+					 pages, flags);
 }
 EXPORT_SYMBOL(get_user_pages_unlocked);
 

virt/kvm/kvm_main.c

@@ -1352,10 +1352,15 @@ static int hva_to_pfn_slow(unsigned long addr, bool *async, bool write_fault,
 		npages = get_user_page_nowait(current, current->mm,
 					      addr, write_fault, page);
 		up_read(&current->mm->mmap_sem);
-	} else
+	} else {
+		unsigned int flags = FOLL_TOUCH | FOLL_HWPOISON;
+
+		if (write_fault)
+			flags |= FOLL_WRITE;
+
 		npages = __get_user_pages_unlocked(current, current->mm, addr, 1,
-						   write_fault, 0, page,
-						   FOLL_TOUCH|FOLL_HWPOISON);
+						   page, flags);
+	}
 	if (npages != 1)
 		return npages;