mm: add a pmd_fault handler

mm: add a pmd_fault handler

Orabug: 22913653

Allow non-anonymous VMAs to provide huge pages in response to a page fault.

Signed-off-by: Matthew Wilcox <willy@linux.intel.com>
Cc: Hillf Danton <dhillf@gmail.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Theodore Ts'o <tytso@mit.edu>
Cc: Jan Kara <jack@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
(cherry picked from commit b96375f74a6d4f39fc6cbdc0bce5175115c7f96f)
Signed-off-by: Dan Duval <dan.duval@oracle.com>
NOTE: Moved new member to the end of the vm_operations_struct and
surrounded their definitions with #ifdef __GENKSYMS__/#endif so as
to maintain kABI.  - Dan Duval <dan.duval@oracle.com>