I have managed to compile Xen, the kernel, COLO, following the 
information in this thread.
http://lists.xenproject.org/archives/html/xen-devel/2016-02/msg03507.html

Github branche : changlox/colo_v12
https://github.com/Pating/xen/tree/changlox/colo_v12

Xen (COLO version) is now compiled and installed, the kernel patched and 
network cards are configured as in the documentation below:
http://wiki.xen.org/wiki/COLO_-_Coarse_Grain_Lock_Stepping


When I try to start a virtual machine, I receive this error message:

[root@xen1 ~]# xl create /var/virtualStore/test/test.cfg
Parsing config from /var/virtualStore/test/test.cfg
libxl: warning: libxl_dm.c:1447:libxl__build_device_model_args_new: 
Could not find user xen-qemuuser-shared, starting QEMU as root
libxl: error: libxl_device.c:963:device_backend_callback: unable to add 
device with path /local/domain/0/backend/vif/3/0
libxl: error: libxl_create.c:1443:domcreate_attach_vtpms: unable to add 
nic devices
libxl: error: libxl_device.c:963:device_backend_callback: unable to 
remove device with path /local/domain/0/backend/vif/3/0
libxl: error: libxl.c:1638:devices_destroy_cb: libxl__devices_destroy 
failed for 3
libxl: error: libxl.c:1565:libxl__destroy_domid: non-existant domain 3
libxl: error: libxl.c:1523:domain_destroy_callback: unable to destroy 
guest with domid 3
libxl: error: libxl.c:1452:domain_destroy_cb: destruction of domain 3 failed

When I commented the network line in the virtual machine configuration 
file, it works correctly.

I tried with or without COLO in the virtual machine configuration file, 
without success.

Attached, the virtual machine configuration file.

Someone an idea for this problem?