KVM machines freeze with 99% Host CPU

[Jens Neu]

Hi list,
I run two relatively small KVM machines with CentOS 7 on a FC27 Server. 
After some days, both machines freeze - both of them, with short delay 
if at all. On the host the kvm/qemu processes show 99% CPU and they have 
to be removed with e.g. "virsh destroy".

I have this scenario: 
https://forums.fedoraforum.org/showthread.php?317123-qemu-takes-100-of-a-cor...

It happens on kernels 4.14 as well as 4.15. The host itself has no 
problems, there are no errors in logs. Any hints where to debug this?

regards
Jens