Wednesday, February 6, 2013

Enable Nested KVM Machines with Fedora 18

KVM on top of KVM

Nested KVM allows you to run a KVM virtual machine on top of an already virtualized machine (yo dawg). Why would you want to do this? Well for me it is simple I want to test some KVM tools out without using actual hardware. Another use case might be for somebody who purchases a beefy "cloud" machine and wants to split that up into smaller pieces.

How To Do It?

Some configuration needs to happen on the Fedora 18 physical host. You need to enable kvm nested if you are using an Intel processor (AMD has it enabled by default). To do that create or edit /etc/modprobe.d/kvm-intel.conf. Add the line "options kvm-intel nested=1" (without quotes) and reboot your machine. Once the machine has rebooted check to make sure the change took by "cat /sys/module/kvm_intel/parameters/nested". That should return "Y", once you see that you are good to go. Edit your KVM machine and add "vmx" to your CPU features. Bam! virtual machines inside your virtual machines.