Virtualization

Running 64k guests on 4k hosts

When trying to start a VM on a host running with 4k pages, you might see the following error message:

qemu-system-ppc64: Can't support 64 kiB guest pages with 4 kiB host pages with this KVM implementation

There is an easy workaround for this. If running QEMU directly, add the argument -machine pseries,cap-hpt-max-page-size=4096. If running QEMU via libvirt, add the following section to the guest's libvirt XML (via virsh edit [guest name] or the XML tab in virt-manager):

  <features>
    <hpt>
      <maxpagesize unit='KiB'>4</maxpagesize>
    </hpt>
  </features>

Nested KVM

In order to be able to run nested KVM, two things must be satisfied:

1. The kvm_hv kernel module must be loaded with the nested=1 module argument
2. The L1 guest must be started with -machine pseries,cap-nested-hv=on as argument to qemu. If running qemu via libvirt, add the following XML fragment to the XML:

  <features>
    <nested-hv state="on"/>
  </features>

Further Information

• VoidLinux PPC documentation on Virtualization
• QEMU documentation about POWER guests

https://gitlab.com/libvirt/libvirt/-/issues/227#note_705948269