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.

PCI devices are requested through flavor extra specs, specifically via the pci_passthrough:alias=<alias> flavor extra spec. This guide demonstrates how to enable PCI passthrough for a type of PCI device with a vendor ID of 8086 and a product ID of 154d - an Intel X520 Network Adapter - by mapping them to the alias a1. You should adjust the instructions for other devices with potentially different capabilities.

Note

For information on creating servers with SR-IOV network interfaces, refer to the Networking Guide.

Limitations

  • Attaching SR-IOV ports to existing servers is not currently supported. This is now rejected by the API but previously it fail later in the process. See 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 for details.

Note

Nova only supports PCI addresses where the fields are restricted to the following maximum value:

  • domain - 0xFFFF

  • bus - 0xFF

  • slot - 0x1F

  • function - 0x7

Nova will ignore PCI devices reported by the hypervisor if the address is outside of these ranges.

Configure host (Compute)

To enable PCI passthrough on an x86, Linux-based compute node, the following are required:

  • VT-d enabled in the BIOS

  • IOMMU enabled on the host OS, e.g. by adding the intel_iommu=on or amd_iommu=on parameter to the kernel parameters

  • Assignable PCIe devices

To enable PCI passthrough on a Hyper-V compute node, the following are required:

  • Windows 10 or Windows / Hyper-V Server 2016 or newer

  • VT-d 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:

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.

Configure nova-compute (Compute)

Once PCI passthrough has been configured for the host, nova-compute must be configured to allow the PCI device to pass through to VMs. This is done using the pci.passthrough_whitelist option. For example, assuming our sample PCI device has a PCI address of 41:00.0 on each host:

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

Refer to pci.passthrough_whitelist for syntax information.

Alternatively, to enable passthrough of all devices with the same product and vendor ID:

[pci]
passthrough_whitelist = { "vendor_id": "8086", "product_id": "154d" }

If using vendor and product IDs, all PCI devices matching the vendor_id and product_id are added to the pool of PCI devices available for passthrough to VMs.

In addition, it is necessary to configure the pci.alias option, which is a JSON-style configuration option that allows you to map a given device type, identified by the standard PCI vendor_id and (optional) product_id fields, to an arbitrary name or alias. This alias can then be used to request a PCI device using the pci_passthrough:alias=<alias> flavor extra spec, as discussed previously. For our sample device with a vendor ID of 0x8086 and a product ID of 0x154d, this would be:

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

It’s important to note the addition of the device_type field. This is necessary because this PCI device supports SR-IOV. The nova-compute service categorizes devices into one of three types, depending on the capabilities the devices report:

type-PF

The device supports SR-IOV and is the parent or root device.

type-VF

The device is a child device of a device that supports SR-IOV.

type-PCI

The device does not support SR-IOV.

By default, it is only possible to attach type-PCI devices using PCI passthrough. If you wish to attach type-PF or type-VF devices, you must specify the device_type field in the config option. If the device was a device that did not support SR-IOV, the device_type field could be omitted.

Refer to pci.alias for syntax information.

Important

This option must also be configured on controller nodes. This is discussed later in this document.

Once configured, restart the nova-compute service.

Configure nova-scheduler (Controller)

The nova-scheduler service must be configured to enable the PciPassthroughFilter. To do this, add this filter to the list of filters specified in filter_scheduler.enabled_filters and set filter_scheduler.available_filters to the default of nova.scheduler.filters.all_filters. For example:

[filter_scheduler]
enabled_filters = ...,PciPassthroughFilter
available_filters = nova.scheduler.filters.all_filters

Once done, restart the nova-scheduler service.

Configure nova-api (Controller)

It is necessary to also configure the pci.alias config option on the controller. This configuration should match the configuration found on the compute nodes. For example:

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

Refer to pci.alias for syntax information. Refer to Affinity for numa_policy information.

Once configured, restart the nova-api service.

Configure a flavor (API)

Once the alias has been configured, it can be used for an flavor extra spec. For example, to request two of the PCI devices referenced by alias a1, run:

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

For more information about the syntax for pci_passthrough:alias, refer to Flavors.

Create instances with PCI passthrough devices

The nova-scheduler service selects a destination host that has PCI devices available that match the alias specified in the flavor.

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