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

Since 3.12 or more precisely  commit 0944fe3f ("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>
Cc: stable@vger.kernel.org # v3.12+

arch/s390/include/asm/pgtable.h

@@ -1127,7 +1127,7 @@ static inline int ptep_test_and_clear_young(struct vm_area_struct *vma,
 					    unsigned long addr, pte_t *ptep)
 {
 	pgste_t pgste;
-	pte_t pte;
+	pte_t pte, oldpte;
 	int young;
 
 	if (mm_has_pgste(vma->vm_mm)) {
@@ -1135,12 +1135,13 @@ static inline int ptep_test_and_clear_young(struct vm_area_struct *vma,
 		pgste = pgste_ipte_notify(vma->vm_mm, ptep, pgste);
 	}
 
-	pte = *ptep;
+	oldpte = pte = *ptep;
 	ptep_flush_direct(vma->vm_mm, addr, ptep);
 	young = pte_young(pte);
 	pte = pte_mkold(pte);
 
 	if (mm_has_pgste(vma->vm_mm)) {
+		pgste = pgste_update_all(&oldpte, pgste, vma->vm_mm);
 		pgste = pgste_set_pte(ptep, pgste, pte);
 		pgste_set_unlock(ptep, pgste);
 	} else