Hi,

I have a Windows 7 SP1 Pro 64-bit VM which works fine on libvirt 2.3.0 and Qemu 2.7.0.

If I enable HyperV features (https://libvirt.org/formatdomain.html#elementsFeatures) like "relaxed", "spinlocks" etc - VM doesn't boot. "Starting Windows" text appears for ~2 seconds (no flying dots, no logo) and then it just goes to black screen. If I switch HyperV features back off, it boots normally again.

Running VM with debuggging enabled (virsh --log win7_hyperv.log --debug 1 start win7) doesn't produce any errors in the log. There are no logs for that attempted boot in the guest either - apparently it doesn't get to the point when Windows starts logging.

Attaching VM xml definition (with HyperV features enabled).