s390/vmemmap: fallback to PTEs if mapping large PMD fails

Let's fallback to single pages if short on huge pages. No need to stop
memory hotplug.

Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: Christian Borntraeger <borntraeger@de.ibm.com>
Cc: Gerald Schaefer <gerald.schaefer@de.ibm.com>
Signed-off-by: NDavid Hildenbrand <david@redhat.com>
Message-Id: <20200722094558.9828-8-david@redhat.com>
Signed-off-by: NHeiko Carstens <hca@linux.ibm.com>

arch/s390/mm/vmem.c

@@ -180,11 +180,11 @@ static int __ref modify_pmd_table(pud_t *pud, unsigned long addr,
 				 */
 				new_page = vmemmap_alloc_block(PMD_SIZE,
 							       NUMA_NO_NODE);
-				if (!new_page)
-					goto out;
+				if (new_page) {
 					pmd_val(*pmd) = __pa(new_page) | prot;
 					continue;
 				}
+			}
 			pte = vmem_pte_alloc();
 			if (!pte)
 				goto out;