32-bit PV guests and 168 GB boundary

[Nick Pegg <npegg@linode.com>]

Hello,

I've recently ran into a problem on a physical machine with a large
amount of memory where 32-bit PV guests would refuse to boot with this
error message:

xm create: Error: (4, 'Out of memory', "panic: xc_dom_boot.c:159:
xc_dom_boot_mem_init: can't allocate low memory for domain")

We discovered that there's a boundary where 32-bit PV guests can't be
allocated memory above 168GB, along with the work-around config option
to reserve memory for these guests (total_available_memory in
xend-config.sxp).

Could someone clarify why this is a restriction? Is this some sort of
hardware limitation?


Thanks,
Nick