KVM¶

For x86 based systems¶

1. To determine whether the svm or vmx CPU extensions are present, run this command:

   # grep -E 'svm|vmx' /proc/cpuinfo
   

   This command generates output if the CPU is capable of hardware-virtualization. Even if output is shown, you might still need to enable virtualization in the system BIOS for full support.

   If no output appears, consult your system documentation to ensure that your CPU and motherboard support hardware virtualization. Verify that any relevant hardware virtualization options are enabled in the system BIOS.

   The BIOS for each manufacturer is different. If you must enable virtualization in the BIOS, look for an option containing the words virtualization, VT, VMX, or SVM.

2. To list the loaded kernel modules and verify that the kvm modules are loaded, run this command:

   # lsmod | grep kvm
   

   If the output includes kvm_intel or kvm_amd, the kvm hardware virtualization modules are loaded and your kernel meets the module requirements for OpenStack Compute.

   If the output does not show that the kvm module is loaded, run this command to load it:

   # modprobe -a kvm
   

   Run the command for your CPU. For Intel, run this command:

   # modprobe -a kvm-intel
   

   For AMD, run this command:

   # modprobe -a kvm-amd
   

   Because a KVM installation can change user group membership, you might need to log in again for changes to take effect.

   If the kernel modules do not load automatically, use the procedures listed in these subsections.

If the checks indicate that required hardware virtualization support or kernel modules are disabled or unavailable, you must either enable this support on the system or find a system with this support.

If KVM acceleration is not supported, configure Compute to use a different hypervisor, such as QEMU or Xen. See QEMU or XenServer (and other XAPI based Xen variants) for details.

These procedures help you load the kernel modules for Intel-based and AMD-based processors if they do not load automatically during KVM installation.

Intel-based processors

If your compute host is Intel-based, run these commands as root to load the kernel modules:

# modprobe kvm
# modprobe kvm-intel

Add these lines to the /etc/modules file so that these modules load on reboot:

kvm
kvm-intel

AMD-based processors

If your compute host is AMD-based, run these commands as root to load the kernel modules:

# modprobe kvm
# modprobe kvm-amd

Add these lines to /etc/modules file so that these modules load on reboot:

kvm
kvm-amd

For POWER based systems¶

KVM as a hypervisor is supported on POWER system's PowerNV platform.

1. To determine if your POWER platform supports KVM based virtualization run the following command:

   # cat /proc/cpuinfo | grep PowerNV
   

   If the previous command generates the following output, then CPU supports KVM based virtualization.

   platform: PowerNV
   

   If no output is displayed, then your POWER platform does not support KVM based hardware virtualization.

2. To list the loaded kernel modules and verify that the kvm modules are loaded, run the following command:

   # lsmod | grep kvm
   

   If the output includes kvm_hv, the kvm hardware virtualization modules are loaded and your kernel meets the module requirements for OpenStack Compute.

   If the output does not show that the kvm module is loaded, run the following command to load it:

   # modprobe -a kvm
   

   For PowerNV platform, run the following command:

   # modprobe -a kvm-hv
   

   Because a KVM installation can change user group membership, you might need to log in again for changes to take effect.

Host model (default for KVM & QEMU)¶

If your nova.conf file contains cpu_mode=host-model, libvirt identifies the CPU model in /usr/share/libvirt/cpu_map.xml file that most closely matches the host, and requests additional CPU flags to complete the match. This configuration provides the maximum functionality and performance and maintains good reliability and compatibility if the guest is migrated to another host with slightly different host CPUs.

Host pass through¶

If your nova.conf file contains cpu_mode=host-passthrough, libvirt tells KVM to pass through the host CPU with no modifications. The difference to host-model, instead of just matching feature flags, every last detail of the host CPU is matched. This gives the best performance, and can be important to some apps which check low level CPU details, but it comes at a cost with respect to migration. The guest can only be migrated to a matching host CPU.

Custom¶

If your nova.conf file contains cpu_mode=custom, you can explicitly specify one of the supported named models using the cpu_model configuration option. For example, to configure the KVM guests to expose Nehalem CPUs, your nova.conf file should contain:

[libvirt]
cpu_mode = custom
cpu_model = Nehalem

None (default for all libvirt-driven hypervisors other than KVM & QEMU)¶

If your nova.conf file contains cpu_mode=none, libvirt does not specify a CPU model. Instead, the hypervisor chooses the default model.

Guest agent support¶

Use guest agents to enable optional access between compute nodes and guests through a socket, using the QMP protocol.

To enable this feature, you must set hw_qemu_guest_agent=yes as a metadata parameter on the image you wish to use to create the guest-agent-capable instances from. You can explicitly disable the feature by setting hw_qemu_guest_agent=no in the image metadata.