While installing RHEV Hypervisor 3.3 on Oracle VirtualBox I am getting following message:

```
Failed to open a session for the virtual machine RhevH1
VT-x is used by another hypervisor.
(VERR_VMX__IN_VMX_ROOT_MODE).
VirtualBox Can't operate in VMX root mode. Please disable the KVM
kernel extension, recompile your kernel and reboot
(VERR_VMX_IN_VMX_ROOT_MODE).

```

What are the possible solutions are there for this?