diff options
Diffstat (limited to 'arch/s390/mm/gup.c')
| -rw-r--r-- | arch/s390/mm/gup.c | 9 |
1 files changed, 8 insertions, 1 deletions
diff --git a/arch/s390/mm/gup.c b/arch/s390/mm/gup.c index 9b5b866d8adf..5389bf5bc828 100644 --- a/arch/s390/mm/gup.c +++ b/arch/s390/mm/gup.c @@ -287,7 +287,14 @@ int get_user_pages_fast(unsigned long start, int nr_pages, int write, might_sleep(); start &= PAGE_MASK; - nr = __get_user_pages_fast(start, nr_pages, write, pages); + /* + * The FAST_GUP case requires FOLL_WRITE even for pure reads, + * because get_user_pages() may need to cause an early COW in + * order to avoid confusing the normal COW routines. So only + * targets that are already writable are safe to do by just + * looking at the page tables. + */ + nr = __get_user_pages_fast(start, nr_pages, 1, pages); if (nr == nr_pages) return nr; |