RE: [Xen-devel] Kernel BUGatarch/x86_64/mm/../../i386/mm/hypervisor.c:197

[Christophe Saout <christophe@xxxxxxxx>]

Hello Ian,

> > When running on 4GB of total memory instead of 12GB, 
> > everything is just fine. (the three virtual machines, Dom0 + 
> > 2 x DomU are assigned 1GB of memory each, in both test runs). 
> > Does that help?
> 
> Are you setting mem=4096M on the Xen command line? If you removed DIMMs
> to get 4GB in the machine some of the memory willl still be mapped above
> 4GB.
> 
> It seems hard to imagine this is a lurking 4GB issue (especially on
> x86_64 rather tha PAE).

The good news is that we were able to fix this problem by changing BIOS
settings concerning "memory holes". There were two settings "hardware
memory hole" and "software memory hole" that "enable software/hardware
remapping around memory hole", whatever that is. They were both turned
on by default, and I just turned them off. I didn't see any downsides
except that I'm unable to crash the machine any more. It's surviving my
stress tests for several hours now without crashes.

The BIOS help also says that the "hardware memory hole" only works on
REV E0 processors, so perhaps this configures some weird mapping that
Xen doesn't understand? Anyway, I'll stick with this setting now, given
that it just works.

Sorry for all the confusion.

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