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Description of problem:
idle windows 10 guests consume > 50%cpu

Version-Release number of selected component (if applicable):
http://cbs.centos.org/kojifiles/packages/qemu-kvm-ev/2.10.0/21.el7_5.4.1/src/qemu-kvm-ev-2.10.0-21.el7_5.4.1.src.rpm

How reproducible:
always

Steps to Reproduce:
1. run windows 1803 (or server 2019 insider) guest, uefi q35
2.
3.

Actual results:
idle guest takes >50% of host cpu

Expected results:
windows idle guest consumes 2-3% cpu (ideally zero like linux, but that's a different bug)

Additional info:
#1336517 disabled several hyper-v features.
the impact is windows 10 idle guests take big cpu cycles on host.
After learning from https://bugs.launchpad.net/qemu/+bug/1775702/comments/3 that I need hv-synic and hv-stimer, I've rebuilt locally qemu-kvm-ev-2.10.0-21.el7_5.4.1.src.rpm by reverting the "if 0" to "if 1" around these lines:

    DEFINE_PROP_BOOL("hv-synic", X86CPU, hyperv_synic, false),
    DEFINE_PROP_BOOL("hv-stimer", X86CPU, hyperv_stimer, false),

now guest cpu usage is down to 2-3% (needs kernel 4.2+ because ovmf secure boot needed by win10 images downloaded from ms ie modern.ie is supported only by kvm in kernel 4.2 or later)

please revert #1336517

thanks.