Windows Guest on KVM running "single core" after windows update

Hey all, I have a Windows 10 pro (64bit) long time running as a libvirt/KVM guest that I think Windows Update finally narfed. The hardware is a supermicro motherboard with dual Intel E5-2640 CPUs for a total of 40 threads and 64GB The guest is allocated 2sockets, 5cores, 2 threads and 32GB of RAM. (I've also tried 1 socket, 20 cores, 1 thread and 1s10c2t -- no help) In an SSH session to the linux host (CentOS7 - up to date), htop shows 1 core pegged and abnormal distribution of load (like it used to) even with fun little tools in Windows like the PowerToy -> CPUStress64.exe (i.e. the head CPU will show 90-99% and next thread in HTOP will show like 10% which then trails off to like 5%) Even if I tell CPUStress64.exe to load up 10 or 15 threads worth of 100%. Has anyone else seen this? Thanks,  -Ben