KVM: s390: Fix dat_crste_walk_range() early return

If a walk entry handler for a lower level returns a value,
dat_crste_walk_range() will not return immediately, but instead loop
again and move to the next entry.

This means that some entries are potentially skipped, and early return
is ignored. Skipped entries might lead to all kinds of issues, given
that the caller expects them to not be skipped. Early return is often
used to interrupt a walk when a rescheduling is needed; if it is
ignored it can lead to stalls.

Fix by breaking from the loop immediately if the walk to a lower level
returned non-zero.

Fixes: 2db149a0a6 ("KVM: s390: KVM page table management functions: walks")
Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Reviewed-by: Christian Borntraeger <borntraeger@linux.ibm.com>
Signed-off-by: Christian Borntraeger <borntraeger@linux.ibm.com>

arch/s390/kvm/dat.c

@@ -570,6 +570,8 @@ static long dat_crste_walk_range(gfn_t start, gfn_t end, struct crst_table *tabl
 			else if (walk->ops->pte_entry)
 				rc = dat_pte_walk_range(max(start, cur), min(end, next),
 							dereference_pmd(crste.pmd), walk);
+			if (rc)
+				break;
 		}
 	}
 	return rc;