Recent CPU models were specified using invalid vendor element
<vendor>NAME</vendor>, which was silently ignored due to a bug in the
code which was parsing it.
Some features provided by the recently added CPU models were mentioned
twice for each model. This was a result of automatic generation of the
XML from qemu's CPU configuration file without noticing this redundancy.
By specifying <vendor> element in CPU requirements a guest can be
restricted to run only on CPUs by a given vendor. Host CPU vendor is
also specified in capabilities XML.
The vendor is checked when migrating a guest but it's not forced, i.e.,
guests configured without <vendor> element can be freely migrated.
