UPSTREAM: gup: Introduce FOLL_NOFAULT flag to disable page faults

commit 55b8fe70 upstream

Introduce a new FOLL_NOFAULT flag that causes get_user_pages to return
-EFAULT when it would otherwise trigger a page fault.  This is roughly
similar to FOLL_FAST_ONLY but available on all architectures, and less
fragile.

Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
Signed-off-by: Anand Jain <anand.jain@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
(cherry picked from commit 6e213bc6)
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>
Change-Id: I9042539b7125cfbbd60f2329b19a3016031a81a0