Learn how to enable Nested Virtualization in QEMU. Our KVM Support team is here to help you with your questions and concerns.

Enable Nested Virtualization in QEMU

Did you know that mastering the configuration of nested virtualization using the KVM (Kernel-based Virtual Machine) hypervisor can be a game changer?

Today, we will look at enabling and optimizing nested virtual machines on compatible hardware.

Checking Nested Virtualization Status

Before we begin, we have to check whether nested virtualization is already enabled on our hypervisor. This can be done with a terminal command:

• For Intel:

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

• For AMD:

  $ cat /sys/module/kvm_amd/parameters/nested

If the output is “Y,” nested virtualization is already active. If it’s “N,” the next section tells us how to enable it.

Enabling Nested Virtualization

Did you know that a KVM kernel module parameter controls Nested virtualization?

In fact, we have to open the configuration file which is often located at /etc/modprobe.d/qemu-system-x86.conf.

Then, we will find options related to kvm_intel or kvm_amd. So, this lets us know that nesting is currently disabled.

To enable nesting, we have to modify the nested parameter to a value of 1:

• For Intel:

  options kvm_intel nested=1

• For AMD systems only:

  options kvm_amd nested=1

Then, reload the KVM kernel module to apply the new settings. Furthermore, we have to make sure that no virtual machines are running during this process:

# Unload the module
$ sudo modprobe -r kvm_intel
# Reload the module with new settings
$ sudo modprobe kvm_intel


Here, we must replace kvm_intel with kvm_amd if we have an AMD processor.

Then, repeat the command to check whether nesting is now enabled.

Additionally, we can enable nesting persistently by adding a config file in /etc/modprobe.d

In fact, this is necessary for nested virtualization. In addition to that, you need to tell QEMU to enable virtualization support in the outermost VM by supplying the right CPU argument, e.g.:

nested virtualization. The configuration persists across reboots until we remove nested=1 from the KVM module’s parameters.

Here are some additional Verification and Optimizations:

• • Verify virtualization support in the outermost VM using CPU arguments.
  • Supply the right CPU argument to enable virtualization support, for example:
    -cpu host

    or a more specific option like:

    -cpu Haswell-noTSX-IBRS,vmx=on
  • Also, check for virtualization support inside the outermost VM:

    $ grep -o 'vmx\|svm' /proc/cpuinfo
$ kvm-ok


[Need assistance with a different issue? Our team is available 24/7.]

Conclusion

Today, our Support Engineers demonstrated how to enable Nested Virtualization in QEMU.