cpu-model for custom and host-model would fail on ARM64

[Zhanglei Mao]

Nova-compute cpu-mode can only use “host-passthrough” for arm64 servers, both both “customer” and “host-model” would fail.

[Zhanglei Mao (zhanglei-mao)]

https://docs.openstack.org/nova/latest/user/support-matrix.html
( live migration for aarch64 are not supported)

[Zhanglei Mao (zhanglei-mao)]

To set cpu-mode to customer, need to set cpu-model as well. Normally, we can get as below for x86 servrs.

For example:
ubuntu@hc01:~$ sudo virsh capabilities | awk '/<cpu>/,/<\/cpu>/' | awk '/<model>/,/<\/model>/'
      <model>Skylake-Server-IBRS</model>
ubuntu@hc01:~$

On arm64 server:
ubuntu@nova-a01:~$ sudo virsh capabilities | awk '/<cpu>/,/<\/cpu>/'
    <cpu>
      <arch>aarch64</arch>
      <topology sockets='1' cores='32' threads='1'/>
      <pages unit='KiB' size='4'/>
      <pages unit='KiB' size='64'/>
      <pages unit='KiB' size='2048'/>
      <pages unit='KiB' size='32768'/>
      <pages unit='KiB' size='1048576'/>
    </cpu>
ubuntu@nova-a01:~$

On the arm server, it can't list or show a suitable model.

[Zhanglei Mao (zhanglei-mao)]

To set cpu-mode to host-mode, the server create would fail and log shows as below:

ERROR nova.compute.manager [instance: f779bd3c-dda5-4e10-8916-bd0b8928513b] libvirt.libvirtError: unsupported configuration: CPU mode 'host-model' for aarch64 kvm domain on aarch64 host is not supported by hypervisor