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Windows has support for several paravirt features that it will use when running on Hyper-V, Microsoft's hypervisor. These features are called enlightenments. Many of the features are similar to paravirt functionality that exists with Linux on KVM (virtio, kvmclock, PV EOI, etc.) Nowadays QEMU/KVM can also enable support for several Hyper-V enlightenments. When enabled, Windows VMs running on KVM will use many of the same paravirt optimizations they would use when running on Hyper-V. A number of years ago, a PR was introduced that added a good portion of the code to enable this feature set, but it was never completed. This PR enables the existing features. The previous patch set detailed in #1013 also included the tests. By selecting Windows PV, the enlightenment additions will be applied to the libvirt configuration. This is support on Windows Server 2008 and beyond, so all currently supported versions of Windows Server. In our testing, we've seen benchmark improvements of around 20-25% running on Centos 7 hosts and it is also supported on Centos/RHEL 6.5 and later. Testing on Ubuntu would be appreciated.