Comment 9 for bug 1734856

I tried to verify the case and fix myself which is a prereq for good steps to reproduce for the SRU anyway.
I came up with test steps based on what was initially reported.
$ uvt-simplestreams-libvirt --verbose sync --source http://cloud-images.ubuntu.com/daily arch=ppc64el label=daily release=bionic
$ uvt-kvm create --password=ubuntu cpaelzer-bionic release=bionic arch=ppc64el label=daily
$ for i in {1..20}; do
  h=$(printf "\x$(printf %x $((98+$i)))");
  echo "<disk type='file' device='disk'><driver name='qemu' type='qcow2'/><source file='/var/lib/uvtool/libvirt/images/cpaelzer-bionic-t$i.qcow'/><alias name='virtio-disk0'/><target dev='vd$h' bus='virtio'/></disk>" > disk.xml;
  qemu-img create -f qcow2 /var/lib/uvtool/libvirt/images/cpaelzer-bionic-t$i.qcow 1M;
  virsh attach-device artful-testguest disk.xml;
done
$ virsh console <guest>
# in guest then
$ sudo reboot

That works for me with overall 22 disks.
I see a bunch of those:
  virtioblk_transfer: Access beyond end of device!
  virtioblk_transfer failed! type=0, status = 1

But it boots fine still and all disks are attached just fine.
If instead I add all disks to the device statically before starting it it is the same.
Do I just need more devices - any options to be set?

Please also help to provide working steps to reproduce (that if possible does not contain having 20+ real disks reachable).