Description of problem:
panic occurred when running kernel tier1 testing on xen guest
there were the issue on RHLE5.7GA and RHEL5.8 beta.
 - beaker job:
https://beaker.engineering.redhat.com/jobs/150833 - RHEL5.8 beta
https://beaker.engineering.redhat.com/jobs/150958 - RHEL5.7 GA

also I reserved an ia64 machine with RHEL5.8-Server-20111030.0 tree,
after installing xen, and switch into xen kernel, the system hung with these console info:
...
SAL ACPI: generating DSDT...DONE.
SAL ACPI: generating SSDTs...DONE.
(XEN) Using scheduler: SMP Credit Scheduler (credit)
(XEN) Time init:
(XEN) .... System Time: 63040ns
(XEN) .... scale:               AAAAAAAA
(XEN) num_online_cpus=1, max_cpus=64
(XEN) Brought up 4 CPUs
(XEN) xenoprof: using perfmon.
(XEN) perfmon: version 2.0 IRQ 238
(XEN) perfmon: Itanium 2 PMU detected, 16 PMCs, 18 PMDs, 4 counters (47 bits)
(XEN) Maximum number of domains: 63; 18 RID bits per domain
(XEN) *** LOADING DOMAIN 0 ***
(XEN) Maximum permitted dom0 size: 7584MB
(XEN) elf_parse_binary: phdr: paddr=0x4000000 memsz=0x8e1d00
(XEN) elf_parse_binary: phdr: paddr=0x48f0000 memsz=0x8c10
(XEN) elf_parse_binary: phdr: paddr=0x4900000 memsz=0x62b5a8
(XEN) elf_parse_binary: memory: 0x4000000 -> 0x4f2b5a8
(XEN) elf_xen_addr_calc_check: VIRT_BASE unset, using 0x0
(XEN) elf_xen_addr_calc_check: ELF_PADDR_OFFSET unset, using 0x0
(XEN) elf_xen_addr_calc_check: addresses:
(XEN)     virt_base        = 0x0
(XEN)     elf_paddr_offset = 0x0
(XEN)     virt_offset      = 0x0
(XEN)     virt_kstart      = 0x4000000
(XEN)     virt_kend        = 0x4f2b5a8
(XEN)     virt_entry       = 0x400ff20
(XEN)  Dom0 kernel: 64-bit, lsb, paddr 0x4000000 -> 0x4f2b5a8
(XEN) METAPHYSICAL MEMORY ARRANGEMENT:
(XEN)  Kernel image:  4000000->4f2b5a8
(XEN)  Entry address: 400ff20
(XEN)  Init. ramdisk: 4f30000 len 56d9e3
(XEN)  Start info.:   4f2c000->4f30000
(XEN) Dom0 max_vcpus=4
(XEN) Dom0: 0xf000003017c2c280
(XEN) enable lsapic entry: 0xf000003002a098cc
(XEN) enable lsapic entry: 0xf000003002a098d8
(XEN) enable lsapic entry: 0xf000003002a098e4
(XEN) enable lsapic entry: 0xf000003002a098f0
(XEN) Success Disabling SRAT
(XEN) Success Disabling SLIT
(XEN) Domain0 EFI passthrough: ACPI 2.0=0x3002a09800
(XEN) Scrubbing Free RAM: ....................................done.
(XEN) Xen trace buffers: disabled
(XEN) Std. Loglevel: Errors and warnings
(XEN) Guest Loglevel: Nothing (Rate-limited: Errors and warnings)
(XEN) Xen is relinquishing VGA console.
(XEN) *** Serial input -> DOM0 (type 'CTRL-a' three times to switch input to Xen).

Version-Release number of selected component (if applicable):
RHEL5.7GA & RHEL5.8beta on ia64 arch

How reproducible:
100%

Steps to Reproduce:
1. yum install -y xen
2. reboot and switch into xen kernel
3.
  
Actual results:
the xen kernel boot successfully

Expected results:
the system hung when booting.

Additional info: