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Nested Virtualization in Xen | A Guide

Did you know that the concept of nested virtualization lets us execute a hypervisor within a virtual machine?

This layered approach, with levels denoted as L0, L1, and L2, opens several possibilities for debugging hypervisors in constrained environments and testing expansive virtual deployments on limited physical resources.

Today, we are going to take a close look at nested virtualization, its applications, and how to enable and configure it within XenServer and XCP-ng environments.

Understanding Nested Virtualization Levels

Before we begin, let’s take a look at the different nesting virtualization levels:

• L0 (Level 0):

  The hypervisor runs directly on the physical hardware.
• L1 (Level 1):

  The hypervisor operates as a guest on L0.
• L2 (Level 2):

  The guest runs on the L1 hypervisor.

Applications of Nested Virtualization

Although nested virtualization is handy in different situations like debugging and testing, it is not recommended for production user environments.

In fact, it is primarily used in development and testing activities. In order to enable nested virtualization, our XenServer/XCP-ng hosts must have virtualization extensions enabled.

Xen Orchestra is a user-friendly administration tool for Xen Servers. It simplifies the process of enabling nested virtualization as seen here:

1. First, log in to the Xen Orchestra console for your XenServer/XCP-ng infrastructure.
2. Then, head to VMs under Home and click the VM name. Then stop the VM instance.
3. Now, we have to go to the Advanced tab of the Virtual Machine.
4. Next, toggle the switch to turn on nested virtualization.
5. Then, boot the virtual machine.

Validating Nested Virtualization

To confirm if nested virtualization is available on our host system, follow these steps:

1. First, log in to the instance.
2. Then, run this command:

   $ cat /sys/module/kvm_intel/parameters/nested

   If the command returns ‘Y’ or ‘1,’ the nested virtualization feature is successfully enabled.

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Conclusion

Today, our Support Engineers introduced us to Nested Virtualization in Xen.