diff --git a/hw/s390x/s390-skeys.c b/hw/s390x/s390-skeys.c
index 5da6e52..a9a4ae7 100644
--- a/hw/s390x/s390-skeys.c
+++ b/hw/s390x/s390-skeys.c
@@ -176,7 +176,7 @@
     QEMUS390SKeysState *skeys = QEMU_S390_SKEYS(obj);
     MachineState *machine = MACHINE(qdev_get_machine());
 
-    skeys->key_count = machine->maxram_size / TARGET_PAGE_SIZE;
+    skeys->key_count = machine->ram_size / TARGET_PAGE_SIZE;
     skeys->keydata = g_malloc0(skeys->key_count);
 }
 
diff --git a/hw/s390x/s390-stattrib-kvm.c b/hw/s390x/s390-stattrib-kvm.c
index c7e1f35..f89d8d9 100644
--- a/hw/s390x/s390-stattrib-kvm.c
+++ b/hw/s390x/s390-stattrib-kvm.c
@@ -85,7 +85,7 @@
 {
     KVMS390StAttribState *sas = KVM_S390_STATTRIB(sa);
     MachineState *machine = MACHINE(qdev_get_machine());
-    unsigned long max = machine->maxram_size / TARGET_PAGE_SIZE;
+    unsigned long max = machine->ram_size / TARGET_PAGE_SIZE;
 
     if (start_gfn + count > max) {
         error_report("Out of memory bounds when setting storage attributes");
@@ -104,7 +104,7 @@
 {
     KVMS390StAttribState *sas = KVM_S390_STATTRIB(sa);
     MachineState *machine = MACHINE(qdev_get_machine());
-    unsigned long max = machine->maxram_size / TARGET_PAGE_SIZE;
+    unsigned long max = machine->ram_size / TARGET_PAGE_SIZE;
     /* We do not need to reach the maximum buffer size allowed */
     unsigned long cx, len = KVM_S390_SKEYS_MAX / 2;
     int r;
diff --git a/hw/s390x/s390-virtio-ccw.c b/hw/s390x/s390-virtio-ccw.c
index 895498c..0fa00a9 100644
--- a/hw/s390x/s390-virtio-ccw.c
+++ b/hw/s390x/s390-virtio-ccw.c
@@ -26,6 +26,7 @@
 #include "qemu/ctype.h"
 #include "qemu/error-report.h"
 #include "qemu/option.h"
+#include "qemu/qemu-print.h"
 #include "s390-pci-bus.h"
 #include "sysemu/reset.h"
 #include "hw/s390x/storage-keys.h"
@@ -439,6 +440,26 @@
     s390_cpu_restart(S390_CPU(cs));
 }
 
+static ram_addr_t s390_fixup_ram_size(ram_addr_t sz)
+{
+    /* same logic as in sclp.c */
+    int increment_size = 20;
+    ram_addr_t newsz;
+
+    while ((sz >> increment_size) > MAX_STORAGE_INCREMENTS) {
+        increment_size++;
+    }
+    newsz = sz >> increment_size << increment_size;
+
+    if (sz != newsz) {
+        qemu_printf("Ram size %" PRIu64 "MB was fixed up to %" PRIu64
+                    "MB to match machine restrictions. Consider updating "
+                    "the guest definition.\n", (uint64_t) (sz / MiB),
+                    (uint64_t) (newsz / MiB));
+    }
+    return newsz;
+}
+
 static void ccw_machine_class_init(ObjectClass *oc, void *data)
 {
     MachineClass *mc = MACHINE_CLASS(oc);
@@ -668,6 +689,7 @@
 static void ccw_machine_4_2_class_options(MachineClass *mc)
 {
     ccw_machine_5_0_class_options(mc);
+    mc->fixup_ram_size = s390_fixup_ram_size;
     compat_props_add(mc->compat_props, hw_compat_4_2, hw_compat_4_2_len);
 }
 DEFINE_CCW_MACHINE(4_2, "4.2", false);
diff --git a/hw/s390x/sclp.c b/hw/s390x/sclp.c
index af0bfbc..f0c35aa 100644
--- a/hw/s390x/sclp.c
+++ b/hw/s390x/sclp.c
@@ -327,27 +327,20 @@
 static void sclp_memory_init(SCLPDevice *sclp)
 {
     MachineState *machine = MACHINE(qdev_get_machine());
+    MachineClass *machine_class = MACHINE_GET_CLASS(qdev_get_machine());
     ram_addr_t initial_mem = machine->ram_size;
     int increment_size = 20;
 
     /* The storage increment size is a multiple of 1M and is a power of 2.
-     * The number of storage increments must be MAX_STORAGE_INCREMENTS or fewer.
+     * For some machine types, the number of storage increments must be
+     * MAX_STORAGE_INCREMENTS or fewer.
      * The variable 'increment_size' is an exponent of 2 that can be
      * used to calculate the size (in bytes) of an increment. */
-    while ((initial_mem >> increment_size) > MAX_STORAGE_INCREMENTS) {
+    while (machine_class->fixup_ram_size != NULL &&
+           (initial_mem >> increment_size) > MAX_STORAGE_INCREMENTS) {
         increment_size++;
     }
     sclp->increment_size = increment_size;
-
-    /* The core memory area needs to be aligned with the increment size.
-     * In effect, this can cause the user-specified memory size to be rounded
-     * down to align with the nearest increment boundary. */
-    initial_mem = initial_mem >> increment_size << increment_size;
-
-    machine->ram_size = initial_mem;
-    machine->maxram_size = initial_mem;
-    /* let's propagate the changed ram size into the global variable. */
-    ram_size = initial_mem;
 }
 
 static void sclp_init(Object *obj)
diff --git a/include/hw/boards.h b/include/hw/boards.h
index 236d239..fd4d62b 100644
--- a/include/hw/boards.h
+++ b/include/hw/boards.h
@@ -152,6 +152,12 @@
  *    It also will be used as a way to optin into "-m" option support.
  *    If it's not set by board, '-m' will be ignored and generic code will
  *    not create default RAM MemoryRegion.
+ * @fixup_ram_size:
+ *    Amends user provided ram size (with -m option) using machine
+ *    specific algorithm. To be used by old machine types for compat
+ *    purposes only.
+ *    Applies only to default memory backend, i.e., explicit memory backend
+ *    wasn't used.
  */
 struct MachineClass {
     /*< private >*/
@@ -218,6 +224,7 @@
                                                          unsigned cpu_index);
     const CPUArchIdList *(*possible_cpu_arch_ids)(MachineState *machine);
     int64_t (*get_default_cpu_node_id)(const MachineState *ms, int idx);
+    ram_addr_t (*fixup_ram_size)(ram_addr_t size);
 };
 
 /**
diff --git a/softmmu/vl.c b/softmmu/vl.c
index 4f71ac1..58a40bc 100644
--- a/softmmu/vl.c
+++ b/softmmu/vl.c
@@ -2600,6 +2600,9 @@
     }
 
     sz = QEMU_ALIGN_UP(sz, 8192);
+    if (mc->fixup_ram_size) {
+        sz = mc->fixup_ram_size(sz);
+    }
     ram_size = sz;
     if (ram_size != sz) {
         error_report("ram size too large");
diff --git a/target/s390x/kvm.c b/target/s390x/kvm.c
index 1d6fd6a..7f7ebab 100644
--- a/target/s390x/kvm.c
+++ b/target/s390x/kvm.c
@@ -1768,8 +1768,10 @@
 
 static void insert_stsi_3_2_2(S390CPU *cpu, __u64 addr, uint8_t ar)
 {
+    const MachineState *ms = MACHINE(qdev_get_machine());
+    uint16_t conf_cpus = 0, reserved_cpus = 0;
     SysIB_322 sysib;
-    int del;
+    int del, i;
 
     if (s390_cpu_virt_mem_read(cpu, addr, ar, &sysib, sizeof(sysib))) {
         return;
@@ -1789,6 +1791,19 @@
         memset(sysib.ext_names[del], 0,
                sizeof(sysib.ext_names[0]) * (sysib.count - del));
     }
+
+    /* count the cpus and split them into configured and reserved ones */
+    for (i = 0; i < ms->possible_cpus->len; i++) {
+        if (ms->possible_cpus->cpus[i].cpu) {
+            conf_cpus++;
+        } else {
+            reserved_cpus++;
+        }
+    }
+    sysib.vm[0].total_cpus = conf_cpus + reserved_cpus;
+    sysib.vm[0].conf_cpus = conf_cpus;
+    sysib.vm[0].reserved_cpus = reserved_cpus;
+
     /* Insert short machine name in EBCDIC, padded with blanks */
     if (qemu_name) {
         memset(sysib.vm[0].name, 0x40, sizeof(sysib.vm[0].name));