Description of problem:
guest which start on 7.3 fail to migrate to migrate to 7.4 host after update 

Version-Release number of selected component (if applicable):
libvirt-3.2.0-14.el7.x86_64

How reproducible:
100%

Steps to Reproduce:
1. start a guest on libvirt-2.0.0-10 (rhel7.3) and qemu-kvm-rhev-2.6.0-28.el7_3.12.x86_64 with host-model:

  <cpu mode='host-model'>
    <model fallback='allow'/>
    <numa>
      <cell id='0' cpus='0-2' memory='524288' unit='KiB'/>
      <cell id='1' cpus='3-5' memory='524288' unit='KiB'/>
    </numa>
  </cpu>

# virsh start r7-mig
Domain r7-mig started

2. check qemu command line:

# ps aux|grep qemu
...-cpu Opteron_G5,+vme,+ht,+monitor,+osxsave,+bmi1,+mmxext,+fxsr_opt,+cmp_legacy,+extapic,+cr8legacy,+osvw,+ibs,+skinit,+wdt,+lwp,+tce,+nodeid_msr,+topoext,+perfctr_core,+perfctr_nb

3. update libvirt to libvirt-3.2.0-14.el7 (rhel 7.4):

4. recheck the running guest xml:
# virsh dumpxml r7-mig

  <cpu mode='host-model' check='partial'>
    <model fallback='allow'/>

# virsh dumpxml r7-mig --migratable

  <cpu mode='host-model' check='partial'>
    <model fallback='allow'/>


5. migrate guest to 7.4 host without --xml:

# virsh migrate r7-mig qemu+tcp://target/system --live
error: internal error: qemu unexpectedly closed the monitor: -no-user-config -nodefaults -chardev socket,id=charmonitor,path=/var/lib/libvirt/qemu/domain-12-r7-mig/monitor.sock,server,nowait -mon chardev=charmonitor,id=monitor,mode=control -rtc base=utc,driftfix=slew -global kvm-pit.lost_tick_policy=delay -no-hpet -no-shutdown -global PIIX4_PM.disable_s3=0 -global PIIX4_PM.disable_s4=0 -boot strict=on -device ich9-usb-ehci1,id=usb,bus=pci.0,addr=0x6.0x7 -device ich9-usb-uhci1,masterbus=usb.0,firstport=0,bus=pci.0,multifunction=on,addr=0x6 -device ich9-usb-uhci2,masterbus=usb.0,firstport=2,bus=pci.0,addr=0x6.0x1 -device ich9-usb-uhci3,masterbus=usb.0,firstport=4,bus=pci.0,addr=0x6.0x2 -device virtio-serial-pci,id=virtio-serial0,bus=pci.0,addr=0x5 -chardev pty,id=charserial0 -device pci-serial,chardev=charserial0,id=serial0,bus=pci.0,addr=0x9 -chardev spicevmc,id=charchannel0,name=vdagent -device virtserialport,bus=virtio-serial0.0,nr=1,chardev=charchannel0,id=channel0,name=com.redhat.spice.0 -chardev socket,id=charchannel1,path=

6. check the target host guest log:

2017-06-28T01:25:00.982589Z qemu-kvm: State blocked by non-migratable device 'cpu'
2017-06-28T01:25:00.982703Z qemu-kvm: load of migration failed: Invalid argument

7. check the target qemu command line:

-cpu Opteron_G5,vme=on,ht=on,monitor=on,osxsave=on,bmi1=on,mmxext=on,fxsr_opt=on,cmp_legacy=on,extapic=on,cr8legacy=on,osvw=on,ibs=on,skinit=on,wdt=on,lwp=on,tce=on,nodeid_msr=on,topoext=on,perfctr_core=on,perfctr_nb=on,invtsc=on

you can see that libvirt add a invtsc=on in the qemu command line.

8. src and tgt host have the same cpu:

virsh # capabilities 
...
      <model>Opteron_G5</model>
      <vendor>AMD</vendor>
      <topology sockets='1' cores='4' threads='1'/>
      <feature name='vme'/>
      <feature name='ht'/>
      <feature name='monitor'/>
      <feature name='osxsave'/>
      <feature name='bmi1'/>
      <feature name='mmxext'/>
      <feature name='fxsr_opt'/>
      <feature name='cmp_legacy'/>
      <feature name='extapic'/>
      <feature name='cr8legacy'/>
      <feature name='osvw'/>
      <feature name='ibs'/>
      <feature name='skinit'/>
      <feature name='wdt'/>
      <feature name='lwp'/>
      <feature name='tce'/>
      <feature name='nodeid_msr'/>
      <feature name='topoext'/>
      <feature name='perfctr_core'/>
      <feature name='perfctr_nb'/>
      <feature name='invtsc'/>


Actual results:
guest fail to migrate to target host

Expected results:
migrate success

Additional info: