=== KVM === KVM is configured as the default hypervisor for Compute. .. note:: This document contains several sections about hypervisor selection. If you are reading this document linearly, you do not want to load the KVM module before you install ``nova-compute``. The ``nova-compute`` service depends on qemu-kvm, which installs ``/lib/udev/rules.d/45-qemu-kvm.rules``, which sets the correct permissions on the ``/dev/kvm`` device node. To enable KVM explicitly, add the following configuration options to the ``/etc/nova/nova.conf`` file: .. code-block:: ini compute_driver = libvirt.LibvirtDriver [libvirt] virt_type = kvm The KVM hypervisor supports the following virtual machine image formats: * Raw * QEMU Copy-on-write (qcow2) * QED Qemu Enhanced Disk * VMware virtual machine disk format (vmdk) This section describes how to enable KVM on your system. For more information, see the following distribution-specific documentation: * `Fedora: Virtualization Getting Started Guide `_ from the Fedora 22 documentation. * `Ubuntu: KVM/Installation `_ from the Community Ubuntu documentation. * `Debian: Virtualization with KVM `_ from the Debian handbook. * `Red Hat Enterprise Linux: Installing virtualization packages on an existing Red Hat Enterprise Linux system `_ from the ``Red Hat Enterprise Linux Virtualization Host Configuration and Guest Installation Guide``. * `openSUSE: Installing KVM `_ from the openSUSE Virtualization with KVM manual. * `SLES: Installing KVM `_ from the SUSE Linux Enterprise Server ``Virtualization Guide``. Enable KVM ~~~~~~~~~~ The following sections outline how to enable KVM based hardware virtualization on different architectures and platforms. To perform these steps, you must be logged in as the ``root`` user. For x86 based systems --------------------- #. To determine whether the ``svm`` or ``vmx`` CPU extensions are present, run this command: .. code-block:: console # 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``. #. To list the loaded kernel modules and verify that the ``kvm`` modules are loaded, run this command: .. code-block:: console # 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: .. code-block:: console # modprobe -a kvm Run the command for your CPU. For Intel, run this command: .. code-block:: console # modprobe -a kvm-intel For AMD, run this command: .. code-block:: console # 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. .. note:: Some systems require that you enable VT support in the system BIOS. If you believe your processor supports hardware acceleration but the previous command did not produce output, reboot your machine, enter the system BIOS, and enable the VT option. If KVM acceleration is not supported, configure Compute to use a different hypervisor, such as ``QEMU`` or ``Xen``. See :ref:`compute_qemu` or :ref:`compute_xen_api` 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: .. code-block:: console # modprobe kvm # modprobe kvm-intel Add these lines to the ``/etc/modules`` file so that these modules load on reboot: .. code-block:: console kvm kvm-intel **AMD-based processors** If your compute host is AMD-based, run these commands as root to load the kernel modules: .. code-block:: console # modprobe kvm # modprobe kvm-amd Add these lines to ``/etc/modules`` file so that these modules load on reboot: .. code-block:: console kvm kvm-amd For POWER based systems ----------------------- KVM as a hypervisor is supported on POWER system's PowerNV platform. #. To determine if your POWER platform supports KVM based virtualization run the following command: .. code-block:: console # cat /proc/cpuinfo | grep PowerNV If the previous command generates the following output, then CPU supports KVM based virtualization. .. code-block:: console platform: PowerNV If no output is displayed, then your POWER platform does not support KVM based hardware virtualization. #. To list the loaded kernel modules and verify that the ``kvm`` modules are loaded, run the following command: .. code-block:: console # 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: .. code-block:: console # modprobe -a kvm For PowerNV platform, run the following command: .. code-block:: console # 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. Configure Compute backing storage ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Backing Storage is the storage used to provide the expanded operating system image, and any ephemeral storage. Inside the virtual machine, this is normally presented as two virtual hard disks (for example, ``/dev/vda`` and ``/dev/vdb`` respectively). However, inside OpenStack, this can be derived from one of three methods: ``lvm``, ``qcow`` or ``raw``, chosen using the ``images_type`` option in ``nova.conf`` on the compute node. QCOW is the default backing store. It uses a copy-on-write philosophy to delay allocation of storage until it is actually needed. This means that the space required for the backing of an image can be significantly less on the real disk than what seems available in the virtual machine operating system. RAW creates files without any sort of file formatting, effectively creating files with the plain binary one would normally see on a real disk. This can increase performance, but means that the entire size of the virtual disk is reserved on the physical disk. Local `LVM volumes `__ can also be used. Set ``images_volume_group = nova_local`` where ``nova_local`` is the name of the LVM group you have created. Specify the CPU model of KVM guests ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ The Compute service enables you to control the guest CPU model that is exposed to KVM virtual machines. Use cases include: * To maximize performance of virtual machines by exposing new host CPU features to the guest * To ensure a consistent default CPU across all machines, removing reliance of variable QEMU defaults In libvirt, the CPU is specified by providing a base CPU model name (which is a shorthand for a set of feature flags), a set of additional feature flags, and the topology (sockets/cores/threads). The libvirt KVM driver provides a number of standard CPU model names. These models are defined in the ``/usr/share/libvirt/cpu_map.xml`` file. Check this file to determine which models are supported by your local installation. Two Compute configuration options in the ``[libvirt]`` group of ``nova.conf`` define which type of CPU model is exposed to the hypervisor when using KVM: ``cpu_mode`` and ``cpu_model``. The ``cpu_mode`` option can take one of the following values: ``none``, ``host-passthrough``, ``host-model``, and ``custom``. 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: .. code-block:: ini [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. KVM performance tweaks ~~~~~~~~~~~~~~~~~~~~~~ The `VHostNet `_ kernel module improves network performance. To load the kernel module, run the following command as root: .. code-block:: console # modprobe vhost_net Troubleshoot KVM ~~~~~~~~~~~~~~~~ Trying to launch a new virtual machine instance fails with the ``ERROR`` state, and the following error appears in the ``/var/log/nova/nova-compute.log`` file: .. code-block:: console libvirtError: internal error no supported architecture for os type 'hvm' This message indicates that the KVM kernel modules were not loaded. If you cannot start VMs after installation without rebooting, the permissions might not be set correctly. This can happen if you load the KVM module before you install ``nova-compute``. To check whether the group is set to ``kvm``, run: .. code-block:: console # ls -l /dev/kvm If it is not set to ``kvm``, run: .. code-block:: console # udevadm trigger