Comment # 6 on bug 1172541 from James Carter

"Good" news from a test: I have these two identical machines, one with a
VM and one without; the VM host freezes reliably and the leaf node has
never been seen to freeze.  OK, on the leaf note (Iris) I installed 
qemu-kvm-5.0.0-3.1.x86_64 libvirt-daemon-6.4.0-1.1.x86_64 and numerous
friends (the latest) and created a new VM called Orion, basically 
copying the XML and software selection from my other VMs.  For testing
I ran a console session on the guest (VNC through virt-viewer) and set 
the guest's screensaver to show random eye candy, giving the guest and
host consistent but not excessive net traffic and CPU load.  (I have the
impression that the eye candy is not necessary; just being booted is
enough; but that's not assured and it's more prudent to load up the
guest, to maybe avoid a false negative.)  

With kernel 5.6.12 on the host and 5.7.1 on the guest, it ran for 14 
hours without freezing.  With 5.7.1 on both the host and the guest, it
ran for 5 hours and the host froze up, being rebooted by its watchdog
timer.  I can't tell if the guest had any issues just before the host
froze; I was in bed at the time.  As usual, the log files on both the
host and guest look perfectly normal, then end with a block of \0, 
and continue on with normal-looking output from the rebooted session.  

So this does support the hypothesis that machines running kernel 5.6.14+
(here, 5.7.1) will freeze if and only if they are host to a VM.  It does
not support the alternative fact that the recent update to libvirt and
qemu may have made the host stop freezing.  In the upgrades to 5.6.14
and kernel-default-5.7.0-3.1.gad96a07.x86_64 two of the VM hosts would
freeze within 5 minutes of booting (tried several times each), but hosts
that are less mission critical and more convenient for testing also take
a long time to freeze, if they're going to.

It's going to be hard to get developers to pay attention to this problem
if they can't reproduce it in-house, and I'm going to try to put
together an easily describable software and VM configuration that will
freeze up. 

@tiwai, I retrieved kernel-default-5.6.12-1.3.x86_64 from 
http://download.opensuse.org/history/ , thanks for the link!