Gannet, SPICE Guest Tools is certainly a different problem, you should report that to the spice project instead. And since the original problem was apparently fixed via hv_synic / hv_stimer (if I got the comments right), I'm closing this ticket now.
** Changed in: qemu Status: New => Fix Released -- You received this bug notification because you are a member of qemu- devel-ml, which is subscribed to QEMU. https://bugs.launchpad.net/bugs/1775702 Title: High host CPU load and slower guest after upgrade guest OS Windows 10 to ver 1803 Status in QEMU: Fix Released Bug description: After upgrading Windows 10 guest to version 1803, guests VM runs slower and there is high host CPU load even when guest is almost idle. Did not happened with windows 10 up to version 1709. See my 1st report here: https://askubuntu.com/questions/1033985/kvm-high-host-cpu-load-after-upgrading-vm-to-windows-10-1803 Another user report is here: https://lime-technology.com/forums/topic/71479-windows-10-vm-cpu-usage/ Tested on: Ubuntu 16.04 with qemu 2.5.0 and i3-3217U, Arch with qemu 2.12 i5-7200U, Ubuntu 18.04 qemu 2.11.1 AMD FX-4300. All three platform showing the same slowdown and higher host cpu load with windows 10 1803 VM compared to windows 10 1709 VM. To manage notifications about this bug go to: https://bugs.launchpad.net/qemu/+bug/1775702/+subscriptions