========================================
Attaching physical PCI devices to guests
========================================

The PCI passthrough feature in OpenStack allows full access and direct control
of a physical PCI device in guests. This mechanism is generic for any kind of
PCI device, and runs with a Network Interface Card (NIC), Graphics Processing
Unit (GPU), or any other devices that can be attached to a PCI bus. Correct
driver installation is the only requirement for the guest to properly use the
devices.

Some PCI devices provide Single Root I/O Virtualization and Sharing (SR-IOV)
capabilities. When SR-IOV is used, a physical device is virtualized and appears
as multiple PCI devices. Virtual PCI devices are assigned to the same or
different guests. In the case of PCI passthrough, the full physical device is
assigned to only one guest and cannot be shared.

.. note::

   For information on creating servers with virtual SR-IOV devices, refer to
   the :neutron-doc:`Networking Guide <admin/config-sriov>`.

   **Limitations**

   * Attaching SR-IOV ports to existing servers is not currently supported, see
     `bug 1708433 <https://bugs.launchpad.net/nova/+bug/1708433>`_ for details.
   * Cold migration (resize) of servers with SR-IOV devices attached was not
     supported until the 14.0.0 Newton release, see
     `bug 1512800 <https://bugs.launchpad.net/nova/+bug/1512880>`_ for details.

To enable PCI passthrough, follow the steps below:

#. Configure nova-scheduler (Controller)

#. Configure nova-api (Controller)**

#. Configure a flavor (Controller)

#. Enable PCI passthrough (Compute)

#. Configure PCI devices in nova-compute (Compute)

.. note::

   The PCI device with address ``0000:41:00.0`` is used as an example. This
   will differ between environments.

Configure nova-scheduler (Controller)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

#. Configure ``nova-scheduler`` as specified in :neutron-doc:`Configure
   nova-scheduler
   <admin/config-sriov.html#configure-nova-scheduler-controller>`.

#. Restart the ``nova-scheduler`` service.

Configure nova-api (Controller)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

#. Specify the PCI alias for the device.

   Configure a PCI alias ``a1`` to request a PCI device with a ``vendor_id`` of
   ``0x8086`` and a ``product_id`` of ``0x154d``. The ``vendor_id`` and
   ``product_id`` correspond the PCI device with address ``0000:41:00.0``.

   Edit ``/etc/nova/nova.conf``:

   .. code-block:: ini

      [pci]
      alias = { "vendor_id":"8086", "product_id":"154d", "device_type":"type-PF", "name":"a1" }

   Refer to :oslo.config:option:`pci.alias` for syntax information.

#. Restart the ``nova-api`` service.

Configure a flavor (Controller)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Configure a flavor to request two PCI devices, each with ``vendor_id`` of
``0x8086`` and ``product_id`` of ``0x154d``:

.. code-block:: console

   # openstack flavor set m1.large --property "pci_passthrough:alias"="a1:2"

For more information about the syntax for ``pci_passthrough:alias``, refer to
:ref:`Flavors <extra-spec-pci-passthrough>`.

Enable PCI passthrough (Compute)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Enable VT-d and IOMMU. For more information, refer to steps one and two in
:neutron-doc:`Create Virtual Functions
<admin/config-sriov.html#create-virtual-functions-compute>`.

For Hyper-V compute nodes, the requirements are as follows:

* Windows 10 or Windows / Hyper-V Server 2016 or newer.
* VT-d and SR-IOV enabled on the host.
* Assignable PCI devices.

In order to check the requirements above and if there are any assignable PCI
devices, run the following Powershell commands:

.. code-block:: console

    Start-BitsTransfer https://raw.githubusercontent.com/Microsoft/Virtualization-Documentation/master/hyperv-samples/benarm-powershell/DDA/survey-dda.ps1
     .\survey-dda.ps1

If the compute node passes all the requirements, the desired assignable PCI
devices to be disabled and unmounted from the host, in order to be assignable
by Hyper-V. The following can be read for more details: `Hyper-V PCI
passthrough`__.

.. __: https://blogs.technet.microsoft.com/heyscriptingguy/2016/07/14/passing-through-devices-to-hyper-v-vms-by-using-discrete-device-assignment/

Configure PCI devices (Compute)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

#. Configure ``nova-compute`` to allow the PCI device to pass through to
   VMs. Edit ``/etc/nova/nova.conf``:

   .. code-block:: ini

      [pci]
      passthrough_whitelist = { "address": "0000:41:00.0" }

   Alternatively specify multiple PCI devices using whitelisting:

   .. code-block:: ini

      [pci]
      passthrough_whitelist = { "vendor_id": "8086", "product_id": "10fb" }

   All PCI devices matching the ``vendor_id`` and ``product_id`` are added to
   the pool of PCI devices available for passthrough to VMs.

   Refer to :oslo.config:option:`pci.passthrough_whitelist` for syntax
   information.

#. Specify the PCI alias for the device.

   From the Newton release, to resize guest with PCI device, configure the PCI
   alias on the compute node as well.

   Configure a PCI alias ``a1`` to request a PCI device with a ``vendor_id`` of
   ``0x8086`` and a ``product_id`` of ``0x154d``. The ``vendor_id`` and
   ``product_id`` correspond the PCI device with address ``0000:41:00.0``.

   Edit ``/etc/nova/nova.conf``:

   .. code-block:: ini

      [pci]
      alias = { "vendor_id":"8086", "product_id":"154d", "device_type":"type-PF", "name":"a1" }

   Refer to :oslo.config:option:`pci.alias` for syntax information.

#. Restart the ``nova-compute`` service.

Create instances with PCI passthrough devices
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The ``nova-scheduler`` selects a destination host that has PCI devices
available with the specified ``vendor_id`` and ``product_id`` that matches the
``alias`` from the flavor.

.. code-block:: console

   # openstack server create --flavor m1.large --image cirros-0.3.5-x86_64-uec --wait test-pci
