UPSTREAM: iov_iter: Introduce nofault flag to disable page faults

commit 3337ab08 upstream

Introduce a new nofault flag to indicate to iov_iter_get_pages not to
fault in user pages.

This is implemented by passing the FOLL_NOFAULT flag to get_user_pages,
which causes get_user_pages to fail when it would otherwise fault in a
page. We'll use the ->nofault flag to prevent iomap_dio_rw from faulting
in pages when page faults are not allowed.

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 f86f8d27)
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>
Change-Id: I6a03ed603ee208ea1b1d515ab500ab6349ffd7cb