How recent? Is it present in Xen 4.8-fc25 (R4.0)? Xen 4.12-fc29 (R4.1)?

Well, maybe the "recent" was not accurate, as in R4.0 this started after 
xen- - from mid 2018.
In R4.1 this issue is there from the beginning, as it was not fixed since - 
being a minor problem affecting few (not so modern Fam15h) systems.

> For many AMD systems (eg. Trinity/Richland) CPUID changes after suspend 
> (some of the high bits),
> > resulting in Xen Panic (see xen/arch/x86/acpi/power.c). So, more 
> investigation would be needed to
> > check why the CPUID bits are changing after resume and whether it had 
> any security implications or
> > not.
> > For the time being - if you accept the possible security implications - 
> you can disable that check
> > eg. by commenting the panic line out after "recheck_cpu_features" in the 
> above mentioned power.c
> > file, compile xen for dom0 via qubes builder and test it in your system.
> Thanks for the info.
> I'm not sure this is the problem, though, because I get the same symptoms 
> when suspending in a Fedora 25 livecd. Which makes me think it's a Fedora 
> problem not a Xen problem, at least for R4.0. In Fedora 29 I think the 
> symptoms were slightly different, the system was responsive but the screen 
> just didn't power back on after resume. I don't think suspend/resume 
> actually worked correctly until Fedora 30. We should have an F31-based R4.1 
> developer release by the end of the month, which would be a more accurate 
> test.
> What are the symptoms of a Xen panic? Would it prevent the screen from 
> powering back on? Would it reboot after five seconds? Or would it just hang?
> I'll try booting qubes R4.1 on bare metal without Xen and try 
> suspend/resume. If it works I'll post cpuinfo before and after. 

As I remember, distribution releases (Fedora, Debian) without Xen were OK 
for me, however, with upstream Xen installed, obviously all had this 
suspend issue.
I don't have a debug card, so the symptoms are: when the computer wakes up 
with this issue, the screen remains blank and the processor start to heat 
up and the PC remains unresponsive. It doesn't turn off automatically you 
have to forcibly turn it off using the power button >5 sec.

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