Bug#622306: 2.6.32-33 Xen amd64 kernel fails to boot as Xen guest

[Reid Barton <rwbarton@ksplice.com>]

Package: linux-image-2.6.32-5-xen-amd64
Version: 2.6.32-33

We were unable to boot the Xen amd64 flavor of the 2.6.32-32 or
2.6.32-33 proposed kernels as a Xen guest.  The failure occurs very
early, before the kernel prints any messages to the console; the guest
machine shows up in xm list as "crashed".

git bisect indicated that the commit "x86: Cleanup highmap after brk
is concluded" is the probable culprit.  It seems this patch has caused
problems for others as well, see for example
https://bugs.launchpad.net/system76/+bug/752870.  We haven't yet
tested whether the "x86, hibernate: Initialize mmu_cr4_features during
boot" commit mentioned in that thread fixes the boot as a Xen guest.

Regards,
Reid Barton