Comment 23 for bug 1769053

Description of problem:
Based on a discussion about Qemus ability to work with Guests >1TB [1] it was identified that it might be wise to have libvirt be able to:
  a) add a setting to the XML to specify the phys-bits
  b) It should be possible for libvirt to check the host it's on can
     satisfy that requirement (enough HW phys bits)
  c) libvirt can check that if RAM > 2^phys-bits it can complain

It is known that (c) can't catch all, as it might still fail if RAM+rounding+pci+hotplug space goes over the limit. Figuring that limit out is tricky and should not be part of the scope here.

[1]: https://bugs.launchpad.net/ubuntu/+source/libvirt/+bug/1769053

Version-Release number of selected component (if applicable):
Up to latest 4.3

How reproducible:
100% - well it essentially is a feature request not an error

Steps to Reproduce:
1. try to control phys-bits through libvirt xml/api

Actual results:
No option exposed to do so.

Expected results:
Be able to control phys-bits

Additional info:
See the discussion on Launchpad [1] for more details of the qemu side of this.