kaiser: ENOMEM if kaiser_pagetable_walk() NULL

kaiser: ENOMEM if kaiser_pagetable_walk() NULL

kaiser_add_user_map() took no notice when kaiser_pagetable_walk() failed.
And avoid its might_sleep() when atomic (though atomic at present unused).

Signed-off-by: Hugh Dickins <hughd@google.com>
Acked-by: Jiri Kosina <jkosina@suse.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
(cherry picked from commit 407c3ff6a24c7cb418b77a124d17e282f9622037)
Signed-off-by: Pavel Tatashin <pasha.tatashin@oracle.com>
Orabug: 27333760
CVE: CVE-2017-5754

Conflicts:
	arch/x86/mm/kaiser.c

Signed-off-by: Kirtikar Kashyap <kirtikar.kashyap@oracle.com>