[libvirt] inquiry, get native capabilities of the host

Hello, I'm interested in getting native capabilities of host CPU using libvirt. I've looked at .../src/cpu/cpu_map.xml. And it does describe native capabilities of host CPU very well. But, libvirt always returns a subset of the native capabilities which is far different from the feature lists in the xml file. (I'm testing with <model name='Westmere'>.) The sponsor of my project is interested is high-performance computing. And knowing native feature of the host CPU that can also be available to a virtual machine is very important for performance reason. I couldn't find how to get the native features of the host that is described in .../src/cpu/cpu_map.xml. Is there a way or libvirt API to get the native capabilities of host CPU that is well described in .../src/cpu/cpu_map.xml? Thanks, David.