Description of problem:
"kernel panic - not syncing: Attempted to kill init!" when boot rhel6-i386 with sse4.2 on host not support sse4.2

Version-Release number of selected component (if applicable):
kvm-83-223.el5

How reproducible:
100% 

Steps to Reproduce:
1. cmd
/usr/libexec/qemu-kvm -drive file=/images/RHEL-Server-6.0-32.qcow2,index=0,if=ide,media=disk,cache=none,format=qcow2 -net nic,vlan=0,model=rtl8139,macaddr=00:1a:20:68:80:e6 -net tap,vlan=0,script=/kvm/scripts/qemu-ifup-switch,downscript=no -m 2048 -smp 2,cores=1,threads=1,sockets=2 -cpu qemu64,+sse2,+sse4.2 -vnc :1 -rtc-td-hack -M rhel5.6.0 -usbdevice tablet -no-kvm-pit-reinjection -boot c -monitor stdio
2.
3.
  
Actual results:
"kernel panic - not syncing: Attempted to kill init!"

Expected results:


Additional info:
1. host
kernel: 2.6.18-237.el5

cpu:
processor	: 3
vendor_id	: GenuineIntel
cpu family	: 6
model		: 23
model name	: Intel(R) Core(TM)2 Quad CPU    Q9400  @ 2.66GHz
stepping	: 10
cpu MHz		: 2000.000
cache size	: 3072 KB

flags		: fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm syscall nx lm constant_tsc pni monitor ds_cpl vmx smx est tm2 ssse3 cx16 xtpr sse4_1 lahf_lm

[root@intel-q9400-4-2 kvm]# cat /proc/cmdline 
ro root=/dev/VolGroup00/LogVol00 console=ttyS0,115200 console=tty0

2. can not reproduce when boot without sse4.2
3. can not reproduce on i7 host (support sse4.2)

processor	: 7
vendor_id	: GenuineIntel
cpu family	: 6
model		: 26
model name	: Intel(R) Core(TM) i7 CPU         920  @ 2.67GHz

flags		: fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm syscall nx rdtscp lm constant_tsc ida nonstop_tsc pni monitor ds_cpl vmx est tm2 ssse3 cx16 xtpr sse4_1 sse4_2 popcnt lahf_lm

3. guest
2.6.32-71.el6.i686