userfaultfd: hugetlbfs: add copy_huge_page_from_user for hugetlb userfaultfd support

userfaultfd: hugetlbfs: add copy_huge_page_from_user for hugetlb userfaultfd support

Orabug: 21685254

userfaultfd UFFDIO_COPY allows user level code to copy data to a page at
fault time.  The data is copied from user space to a newly allocated huge
page.  The new routine copy_huge_page_from_user performs this copy.

Link: http://lkml.kernel.org/r/20161216144821.5183-17-aarcange@redhat.com
Signed-off-by: Mike Kravetz <mike.kravetz@oracle.com>
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Cc: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
Cc: Hillf Danton <hillf.zj@alibaba-inc.com>
Cc: Michael Rapoport <RAPOPORT@il.ibm.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Pavel Emelyanov <xemul@parallels.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
(cherry picked from linux-next next-20170117
 commit 33424a2bf04a630438a7bb8d53a2477ba7527164)
Signed-off-by: Mike Kravetz <mike.kravetz@oracle.com>
Reviewed-by: Dhaval Giani <dhaval.giani@oracle.com>
Signed-off-by: Dhaval Giani <dhaval.giani@oracle.com>