RFE: enable more Hyper-V enlightenments by default

[crobinso]

Originally filed here: https://bugzilla.redhat.com/show_bug.cgi?id=1851244

virt-install currently enables hv-time,hv-relaxed,hv-vapic,hv-spinlocks=0x1fff for guests which
support Hyper-V. There are several additional Hyper-V enlightenments supported by
QEMU and libvirt (see https://github.com/qemu/qemu/blob/master/docs/hyperv.txt and
https://libvirt.org/formatdomain.html#elementsFeatures) which could be useful to enable.
In particular, hv_stimer significantly reduces CPU usage when supporting
VMs are paused (see https://lore.kernel.org/kvm/20200625201046.GA179502@kevinolos/).

[crobinso]

There's also this RHEL virt-manager bug: https://bugzilla.redhat.com/show_bug.cgi?id=1717616
And this qemu discussion may be relevant: https://www.spinics.net/lists/kvm/msg219359.html

We need to start a discussion with qemu devs to understand what should be enabled by
default, and what things we need to consider to do so, like OS support, host support, etc

[crobinso]

Latest plan seems to be to add a convenience option like hyperv=on to qemu comand line: https://bugzilla.redhat.com/show_bug.cgi?id=1877467

That let's qemu determine a reasonable default set based on host capabilities. When that lands and is wired up through libvirt that's what virt-manager should use.

[bryantclcqq]

Does Hyper-V enlightenments supported in arm/aarch64 machine with windows 11 for arm guest? How to enable them to get better performance?