Comment 16 for bug 1921880

I haven't went into too much depth on this for this sniff test, but
migrations also didn't trigger issues for me into the new builds and back.

I tried a host-passthrough and a host-model migration, the latter was expanded
to (started on the old host):
    <model fallback='forbid'>EPYC-Rome</model>
    <vendor>AMD</vendor>
    <feature policy='require' name='pcid'/>
    <feature policy='require' name='x2apic'/>
    <feature policy='require' name='tsc-deadline'/>
    <feature policy='require' name='hypervisor'/>
    <feature policy='require' name='tsc_adjust'/>
    <feature policy='require' name='erms'/>
    <feature policy='require' name='vaes'/>
    <feature policy='require' name='vpclmulqdq'/>
    <feature policy='require' name='spec-ctrl'/>
    <feature policy='require' name='stibp'/>
    <feature policy='require' name='arch-capabilities'/>
    <feature policy='require' name='ssbd'/>
    <feature policy='require' name='xsaves'/>
    <feature policy='require' name='cmp_legacy'/>
    <feature policy='require' name='amd-ssbd'/>
    <feature policy='require' name='virt-ssbd'/>
    <feature policy='require' name='rdctl-no'/>
    <feature policy='require' name='skip-l1dfl-vmentry'/>
    <feature policy='require' name='mds-no'/>
    <feature policy='require' name='pschange-mc-no'/>
    <feature policy='require' name='topoext'/>
  </cpu>

No problem due to the new type being around.
Migration forward and back worked fine.

Obviously new types can't be migrated back, but that never was required.