Chapter 22. Creating nested virtual machines

• Creating a nested virtual machine on Intel
• Creating a nested virtual machine on AMD

• Creating a nested virtual machine on Intel
• Creating a nested virtual machine on AMD
• Creating a nested virtual machine on IBM Z

• Currently, Red Hat tests nesting only on RHEL-KVM. When RHEL is used as the L0 hypervisor, you can use RHEL or Windows as the L1 hypervisor.
• When using an L1 RHEL VM on a non-KVM L0 hypervisor, such as VMware ESXi or Amazon Web Services (AWS), creating L2 VMs in the RHEL guest operating system has not been tested and might not work.

• Use of L2 VMs as hypervisors and creating L3 guests has not been properly tested and is not expected to work.
• Migrating VMs currently does not work on AMD systems if nested virtualization has been enabled on the L0 host.

• On an IBM Z system, huge-page backing storage and nested virtualization cannot be used at the same time.

  # modprobe kvm hpage=1 nested=1
  modprobe: ERROR: could not insert 'kvm': Invalid argument
  # dmesg |tail -1
  [90226.508366] kvm-s390: A KVM host that supports nesting cannot back its KVM guests with huge pages

• Some features available on the L0 host might be unavailable for the L1 hypervisor.

Prerequisites

• An L0 RHEL 9 host running an L1 virtual machine (VM).
• The hypervisor CPU must support nested virtualization. To verify, use the cat /proc/cpuinfo command on the L0 hypervisor. If the output of the command includes the vmx and ept flags, creating L2 VMs is possible. This is generally the case on Intel Xeon v3 cores and later.

• Ensure that nested virtualization is enabled on the L0 host:

  # cat /sys/module/kvm_intel/parameters/nested

  • If the command returns 1 or Y, the feature is enabled. Skip the remaining prerequisite steps, and continue with the Procedure section.

  • If the command returns 0 or N but your system supports nested virtualization, use the following steps to enable the feature.

    1. Unload the kvm_intel module:

       # modprobe -r kvm_intel

    2. Activate the nesting feature:

       # modprobe kvm_intel nested=1

    3. The nesting feature is now enabled, but only until the next reboot of the L0 host. To enable it permanently, add the following line to the /etc/modprobe.d/kvm.conf file:

       options kvm_intel nested=1

Prerequisites

• An L0 RHEL 9 host running an L1 virtual machine (VM).
• The hypervisor CPU must support nested virtualization. To verify, use the cat /proc/cpuinfo command on the L0 hypervisor. If the output of the command includes the svm and npt flags, creating L2 VMs is possible. This is generally the case on AMD EPYC cores and later.

• Ensure that nested virtualization is enabled on the L0 host:

  # cat /sys/module/kvm_amd/parameters/nested

  • If the command returns 1 or Y, the feature is enabled. Skip the remaining prerequisite steps, and continue with the Procedure section.

  • If the command returns 0 or N, use the following steps to enable the feature.

    1. Stop all running VMs on the L0 host.

    2. Unload the kvm_amd module:

       # modprobe -r kvm_amd

    3. Activate the nesting feature:

       # modprobe kvm_amd nested=1

    4. The nesting feature is now enabled, but only until the next reboot of the L0 host. To enable it permanently, add the following to the /etc/modprobe.d/kvm.conf file:

       options kvm_amd nested=1

Prerequisites

• An L0 RHEL 9 host running an L1 virtual machine (VM).
• The hypervisor CPU must support nested virtualization. To verify this is the case, use the cat /proc/cpuinfo command on the L0 hypervisor. If the output of the command includes the sie flag, creating L2 VMs is possible.

• Ensure that nested virtualization is enabled on the L0 host:

  # cat /sys/module/kvm/parameters/nested

  • If the command returns 1 or Y, the feature is enabled. Skip the remaining prerequisite steps, and continue with the Procedure section.

  • If the command returns 0 or N, use the following steps to enable the feature.

    1. Stop all running VMs on the L0 host.

    2. Unload the kvm module:

       # modprobe -r kvm

    3. Activate the nesting feature:

       # modprobe kvm nested=1

    4. The nesting feature is now enabled, but only until the next reboot of the L0 host. To enable it permanently, add the following line to the /etc/modprobe.d/kvm.conf file:

       options kvm nested=1

Procedure

• Create an L2 VM within the L1 VM. To do this, follow the same procedure as when creating the L1 VM.