Older QEMU versions did fixup the ram size to match what can be reported
via sclp. We need to mimic this behaviour for machine types 4.2 and
older to not fail on inbound migration for memory sizes that do not fit.
Old machines with proper aligned memory sizes are not affected.

Alignment table:
 VM size (<=) | Alignment
--------------------------
      1020M   |     1M
      2040M   |     2M
      4080M   |     4M
      8160M   |     8M
     16320M   |    16M
     32640M   |    32M
     65280M   |    64M
    130560M   |   128M
    261120M   |   256M
    522240M   |   512M
   1044480M   |     1G
   2088960M   |     2G
   4177920M   |     4G
   8355840M   |     8G

Suggested action is to replace unaligned -m value with a suitable
aligned one or if a change to a newer machine type is possible, use a
machine version >= 5.0.

A future version might remove the compatibility handling.

For machine types >= 5.0 we can simply use an increment size of 1M and
use the full range of increment number which allows for all possible
memory sizes. The old limitation of having a maximum of 1020 increments
was added for standby memory, which we no longer support. With that we
can now support even weird memory sizes like 10001234 MB.

As we no longer fixup maxram_size as well, make other users use ram_size
instead. Keep using maxram_size when setting the maximum ram size in KVM,
as that will come in handy in the future when supporting memory hotplug
(in contrast, storage keys and storage attributes for hotplugged memory
will have to be migrated per RAM block in the future).

Fixes: 3a12fc61 ("390x/s390-virtio-ccw: use memdev for RAM")
Reported-by: Lukáš Doktor <ldoktor@redhat.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Acked-by: Igor Mammedov <imammedo@redhat.com>
Cc: Igor Mammedov <imammedo@redhat.com>
Cc: Dr. David Alan Gilbert <dgilbert@redhat.com>
Message-Id: <20200401123754.109602-1-borntraeger@de.ibm.com>
[CH: fixed up message on memory size fixup]
Signed-off-by: Cornelia Huck <cohuck@redhat.com>