Oracle Solaris kernel zones on x86-based systems make use of hardware-assisted virtualization features like Oracle VM VirtualBox does. However, for kernel zones and Oracle VM VirtualBox to share this hardware resource, they need to cooperate.

By default, due to performance reasons, Oracle VM VirtualBox acquires the hardware-assisted virtualization resource (VT-x/AMD-V) globally on the host machine and uses it until the last Oracle VM VirtualBox VM that requires it is powered off. This prevents other software from using VT-x/AMD-V during the time Oracle VM VirtualBox has taken control of it.

Oracle VM VirtualBox can be instructed to relinquish use of hardware-assisted virtualization features when not executing guest code, thereby allowing kernel zones to make use of them. To do this, shutdown all Oracle VM VirtualBox VMs and execute the following command:

$ VBoxManage setproperty hwvirtexclusive off

This command needs to be executed only once as the setting is stored as part of the global Oracle VM VirtualBox settings which will continue to persist across host-reboots and Oracle VM VirtualBox upgrades.