KVM: s390/mm: Fix storage key corruption during swapping

KVM: s390/mm: Fix storage key corruption during swapping

commit 3e03d4c46daa849880837d802e41c14132a03ef9 upstream.

Since 3.12 or more precisely  commit 0944fe3f4a32 ("s390/mm:
implement software referenced bits") guest storage keys get
corrupted during paging. This commit added another valid->invalid
translation for page tables - namely ptep_test_and_clear_young.
We have to transfer the storage key into the pgste in that case.

Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Acked-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>