Description of problem:
One particular system doesn't boot when xen and kernel-xen are installed and configured to boot by default. 

Version-Release number of selected component (if applicable):
Xen version 3.1.2-186.el5
kernel-xen-2.6.18-186.el5

How reproducible:
Always on particular hardware/ia64 only

Steps to Reproduce:
1. Install @everything (or just xen, kernel-xen)
2. Reboot after install
3.
  
Actual results:
system doesn't boot. Xen debug messages say panic on CPU0.

Expected results:
System boots.

Additional info:
ELILO boot: Uncompressing Linux... |/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-done
Loading file initrd-2.6.18-186.el5xen.img...|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\done
Loading file vmlinuz-2.6.18-186.el5xen...|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|/-\|done
Uncompressing... done
 __  __            _____  _   ____     _  ___   __        _ ____  
 \ \/ /___ _ __   |___ / / | |___ \   / |( _ ) / /_   ___| | ___| 
  \  // _ \ '_ \    |_ \ | |   __) |__| |/ _ \| '_ \ / _ \ |___ \ 
  /  \  __/ | | |  ___) || |_ / __/|__| | (_) | (_) |  __/ |___) |
 /_/\_\___|_| |_| |____(_)_(_)_____|  |_|\___/ \___(_)___|_|____/ 
                                                                  
 http://www.cl.cam.ac.uk/netos/xen
 University of Cambridge Computer Laboratory

 Xen version 3.1.2-186.el5 (mockbuild) (gcc version 4.1.2 20080704 (Red Hat 4.1.2-46)) Wed Jan 27 18:10:54 EST 2010
 Latest ChangeSet: unavailable

(XEN) Xen command line: BOOT_IMAGE=scsi0:EFI\redhat\xen.gz-2.6.18-186.el5  
(XEN) xen image pstart: 0x4000000, xenheap pend: 0x8000000
(XEN) Xen patching physical address access by offset: 0x0
(XEN) find_memory: efi_memmap_walk returns max_page=221feff9
(XEN) Before xen_heap_start: f0000000041e0c80
(XEN) After xen_heap_start: f000000008624000
(XEN) warning: skipping physical page 0
(XEN) Init boot pages: 0x4000 -> 0x4000000.
(XEN) Init boot pages: 0x8000000 -> 0x1fffc000.
(XEN) Init boot pages: 0x70020000000 -> 0x705fb000000.
(XEN) Init boot pages: 0x78000000000 -> 0x787fc000000.
(XEN) Init boot pages: 0x80000000000 -> 0x807fc000000.
(XEN) Init boot pages: 0x88000000000 -> 0x887f9b91000.
(XEN) Init boot pages: 0x887fa6240a0 -> 0x887fa9b2018.
(XEN) Init boot pages: 0x887fa9b2078 -> 0x887fa9b5fb6.
(XEN) Init boot pages: 0x887fa9b5fea -> 0x887fa9b9000.
(XEN) Init boot pages: 0x887faf9755b -> 0x887faf9e018.
(XEN) Init boot pages: 0x887faf9ee58 -> 0x887fbd9c000.
(XEN) Init boot pages: 0x887fbe80000 -> 0x887fbfe4000.
(XEN) System RAM: 122606MB (125549552kB)
(XEN) size of virtual frame_table: 306736kB
(XEN) virtual machine to physical table: f3fffffeef008038 size: 61488kB
(XEN) max_page: 0x221feff9
(XEN) Xen heap: 17592186044409MB (18014398509475696kB)
(XEN) Cannot handle page request order 1!
(XEN) Xen BUG at page_alloc.c:343
(XEN) FIXME: implement ia64 dump_execution_state()
(XEN) 
(XEN) ****************************************
(XEN) Panic on CPU 0:
(XEN) Xen BUG at page_alloc.c:343
(XEN) ****************************************
(XEN) 
(XEN) Reboot in five seconds...
 MCA event occurred ....