Comment 27 for bug 1921754

Thanks Markus.
Also testing groovy here ...

Before:
++-=====================-================-============-=========================================
ii libvirt-daemon-system 6.6.0-1ubuntu3.4 amd64 Libvirt daemon configuration files
ii qemu-system-x86 1:5.0-5ubuntu9.7 amd64 QEMU full system emulation binaries (x86)

$ qemu-system-x86_64 -cpu ? | grep EPYC-Rome
x86 EPYC-Rome (alias configured by machine type)
x86 EPYC-Rome-v1 AMD EPYC-Rome Processor

After
+++-=====================-================-============-=========================================
ii libvirt-daemon-system 6.6.0-1ubuntu3.5 amd64 Libvirt daemon configuration files
ii qemu-system-x86 1:5.0-5ubuntu9.8 amd64 QEMU full system emulation binaries (x86)

$ qemu-system-x86_64 -cpu ? | grep EPYC-Rome
x86 EPYC-Rome (alias configured by machine type)
x86 EPYC-Rome-v1 AMD EPYC-Rome Processor
x86 EPYC-Rome-v2 AMD EPYC-Rome Processor

Guest with Rome can now control IBRS, both following cpu definitions worked.

  <cpu mode='custom' match='exact' check='partial'>
    <model fallback='forbid'>EPYC-Rome</model>
    <vendor>AMD</vendor>
    <feature policy='require' name='ibrs'/>
  </cpu>

  <cpu mode='custom' match='exact' check='partial'>
    <model fallback='forbid'>EPYC-Rome</model>
    <vendor>AMD</vendor>
    <feature policy='disable' name='ibrs'/>
  </cpu>

Regression tests are still running (on proposed this time), I'll mark it overall verified once those completed as well.