diff --git a/hw/s390x/s390-virtio-ccw.c b/hw/s390x/s390-virtio-ccw.c
index 1c56b70dcd..2ba66be018 100644
--- a/hw/s390x/s390-virtio-ccw.c
+++ b/hw/s390x/s390-virtio-ccw.c
@@ -149,6 +149,7 @@ static void s390_memory_init(MachineState *machine)
     MemoryRegion *sysmem = get_system_memory();
     MemoryRegion *ram = machine->ram;
     uint64_t ram_size = memory_region_size(ram);
+    uint64_t devmem_base, devmem_size;
 
     if (!QEMU_IS_ALIGNED(ram_size, 1 * MiB)) {
         /*
@@ -161,11 +162,31 @@ static void s390_memory_init(MachineState *machine)
         exit(EXIT_FAILURE);
     }
 
-    s390_set_memory_limit(s390ms, ram_size);
+    devmem_size = 0;
+    devmem_base = ram_size;
+#ifdef CONFIG_MEM_DEVICE
+    if (machine->ram_size < machine->maxram_size) {
+
+        /*
+         * Make sure memory devices have a sane default alignment, even
+         * when weird initial memory sizes are specified.
+         */
+        devmem_base = QEMU_ALIGN_UP(devmem_base, 1 * GiB);
+        devmem_size = machine->maxram_size - machine->ram_size;
+    }
+#endif
+    s390_set_memory_limit(s390ms, devmem_base + devmem_size);
 
     /* Map the initial memory. Must happen after setting the memory limit. */
     memory_region_add_subregion(sysmem, 0, ram);
 
+    /* Initialize address space for memory devices. */
+#ifdef CONFIG_MEM_DEVICE
+    if (devmem_size) {
+        machine_memory_devices_init(machine, devmem_base, devmem_size);
+    }
+#endif /* CONFIG_MEM_DEVICE */
+
     /*
      * Configure the maximum page size. As no memory devices were created
      * yet, this is the page size of initial memory only.
diff --git a/hw/s390x/sclp.c b/hw/s390x/sclp.c
index 73e88ab4eb..5945c9b1d8 100644
--- a/hw/s390x/sclp.c
+++ b/hw/s390x/sclp.c
@@ -161,7 +161,11 @@ static void read_SCP_info(SCLPDevice *sclp, SCCB *sccb)
         read_info->rnsize2 = cpu_to_be32(rnsize);
     }
 
-    /* we don't support standby memory, maxram_size is never exposed */
+    /*
+     * We don't support standby memory. maxram_size is used for sizing the
+     * memory device region, which is not exposed through SCLP but through
+     * diag500.
+     */
     rnmax = machine->ram_size >> sclp->increment_size;
     if (rnmax < 0x10000) {
         read_info->rnmax = cpu_to_be16(rnmax);