VirtualBox can't operate in VMX root mode if KVM package is installed

If you installed before a vm using virt-install and try to set up a vm using VirtualBox you obtain the follwoing result: VirtualBox can't operate in VMX root mode
VBox status code: -4011 (VERR_VMX_IN_VMX_ROOT_MODE).
SOLUTION
- uninstall kvm from package manager
- kill all processes that have kvm
- disable kvm module "modprobe -r kvm_intel" with root privileges
In this way you can install ubuntu in Virtual Box