Copying BZ for libvirt, as we need libvirt to support the new boolean flag once we implement it.
This bug was initially created as a copy of Bug #1877467
The set of available hyperv options depend on the host kernel, but this doesn't mean we can't provide a reasonable default set of hyperv features with a simple hyperv=on option.
The default set of hyperv features can depend on the machine type, so new upstream machine types can start enabling newer features, and downstream we can define the default set of hyperv features by just adding compat properties to the rhel machine types.
This way, we'll be able to provide a more reasonable interface for enabling hyperv features (just a boolean option) instead of the complex hyperv flag configuration interface we have today.