xenU - FreeBSD 8.0 CURRENT rev. 197720 kernel panic

I'm trying to get FreeBSD CURRENT working under Xen 3.4.1 using the 
Gentoo dom0 kernel 2.6.29.6
I downloaded and compiled the 8.0 svn version revision 197720 from 
http://svn.freebsd.org/base/head with the KERNCONF=XEN option but when 
I'm starting my domU I'm getting the following panic:

WARNING: loader(8) metadata is missing!
GDB: no debug ports present
KDB: debugger backends: ddb
KDB: current backend: ddb
Copyright (c) 1992-2009 The FreeBSD Project.
Copyright (c) 1979, 1980, 1983, 1986, 1988, 1989, 1991, 1992, 1993, 1994
        The Regents of the University of California. All rights reserved.
FreeBSD is a registered trademark of The FreeBSD Foundation.
FreeBSD 9.0-CURRENT #1 r197720: Sat Oct  3 14:09:31 CEST 2009
    
root_at_freebsd.winnipeg.nl:/usr/local/xen/current-obj/usr/src/sys/XEN-LOTJUH 
i386
WARNING: WITNESS option enabled, expect reduced performance.
Xen reported: 2611.800 MHz processor.
Timecounter "ixen" frequency 1000000000 Hz quality 0
CPU: AMD Phenom(tm) II X4 810 Processor (2611.80-MHz 686-class CPU)
  Origin = "AuthenticAMD"  Id = 0x100f42  Stepping = 2
  
Features=0x178bfbff<FPU,VME,DE,PSE,TSC,MSR,PAE,MCE,CX8,APIC,SEP,MTRR,PGE,MCA,CMOV,PAT,PSE36,CLFLUSH,MMX,FXSR,SSE,SSE2,HTT>
  Features2=0x802009<SSE3,MON,CX16,POPCNT>
  AMD 
Features=0xee500800<SYSCALL,NX,MMX+,FFXSR,Page1GB,RDTSCP,LM,3DNow!+,3DNow!>
  AMD 
Features2=0x37ff<LAHF,CMP,SVM,ExtAPIC,CR8,ABM,SSE4A,MAS,Prefetch,OSVW,IBS,SKINIT,WDT>
  TSC: P-state invariant
Data TLB: 48 entries, fully associative
Instruction TLB: 32 entries, fully associative
L1 data cache: 64 kbytes, 64 bytes/line, 1 lines/tag, 2-way associative
L1 instruction cache: 64 kbytes, 64 bytes/line, 1 lines/tag, 2-way 
associative
L2 internal cache: 512 kbytes, 64 bytes/line, 1 lines/tag, 8-way associative
real memory  = 1073741824 (1024 MB)
Physical memory chunk(s):
0x00000000008ab000 - 0x000000003ecb2fff, 1044414464 bytes (254984 pages)
avail memory = 1040429056 (992 MB)
APIC: Using the MPTable enumerator.
SMP: Added CPU 0 (BSP)
SMP: Added CPU 1 (AP)
SMP: Added CPU 2 (AP)
SMP: Added CPU 3 (AP)
panic: HYPERVISOR_update_va_mapping(((unsigned long)(va)), (pa | 0x002 | 
0x001 | pgeflag | pmap_cache_bits(mode, 0)), UVMF_INVLPG| UVMF_ALL) < 0: 
/usr/src/sys/i386/xen/pmap.c:1269
cpuid = 0
KDB: enter: panic
[thread pid 0 tid 0 ]
Stopped at      kdb_enter+0x3a: movl    $0,kdb_why
db> bt
Tracing pid 0 tid 0 td 0xc03e10f0
kdb_enter(c03698a8,c03698a8,c038e3f1,c06f9cd4,0,...) at kdb_enter+0x3a
panic(c038e3f1,c0396429,c0396207,4f5,0,...) at panic+0x136
pmap_mapdev_attr(0,0,100000,6,c06f9d44,...) at pmap_mapdev_attr+0x13d
pmap_mapbios(0,0,100000,1,c03c946c,...) at pmap_mapbios+0x27
x86bios_intr(c36e4840,0,0,76,c0395e2b,...) at x86bios_intr+0x1b0
module_register_init(c03dbe88,3040800,3040800,6fe000,0,...) at 
module_register_init+0xa7
mi_startup(6fe000,0,0,0,0,...) at mi_startup+0x96
btext() at btext+0x95
db>

I'm getting the same panic when I add only 1 cpu.
I'm using the following boot line for pygrub:
kernel /boot/kernel/kernel 
vfs.root.mountfrom=ufs:xbd0,kern.hz=100,kern.smp.disabled=1,boot_verbose=1,boot_single=1
I've tried it with and without the kern.smp.disabled option

Does anyone have any ideas about what's going wrong?

Lotte-Sara Laan