i faced two serious issues when used Virtualizor in Multi Virtualization mode (BETA) (http://virtualizor.com/wiki/Multi_Virtualization)

My setup: CentOS 6.x 64bit ; Virtualizor installed with kvm flag (--kernel=kvm), then i enabled OpenVZ Multi Virtualization inside Virtualizor and after reboot, i was in old OpenVZ 6 kernel (2.6.3*)

ISSUE 1 - KVM VPS SSH connection was not working, in VNC console i seen black screen, boot menu, grub menu or black/white screen. The CPU was like 99 % used on the VPS, but it extremely slowly boot (not finished booting over night).

SOLUTION: edit KVM VPS configuration and the KVM VPS Plan configuration inside Virtualizor and change value of the "CPU %" variable to "0".

ISSUE 2 - KVM VPS started failing to boot/start with error (found in Virtualizor / Tasks):
error: Failed to create domain from /etc/libvirt/qemu/v100*.xml
error: Unable to create cgroup for v100*: No such file or directory
SOLUTION: open KVM VPS configuration (and "VPS Plans" configuration) in Virtualizor and make sure "CPU units" variables are set to "1000" (not less) and CPU % set to "0" (in KVM VPS's, OpenVZ seems not to be affected). Then do command "service libvirtd restart".

ISSUE 3 - KVM VPS will not work / be killed/stopped if it has too much memory (18000 or 19000 + MB for example)

SOLUTION: "OpenVZ kernel kills KVM VM process if it finds system memory is too low and this VM has a high score of OOM (Out Of Memory), which can be checked for a process using following command:
cat /proc/PID/oom_score

If you dont want kernel to kill processes having this score, you can set
vm.memory_overcommit to 2 both under sysctl.conf and /proc/sys/vm.memory_overcommit

Note, this has a consequence of the whole node to halt (or reboot) if there is high memory usage.

You can search more about OOM_KILLER and configure your server accordingly."