libvirt/docs/drvnodedev.html.in
Boris Fiuczynski 0c841f9b70 node_device: detecting mdev_types capability on CSS devices
Add detection of mdev_types capability to channel subsystem devices.

Signed-off-by: Boris Fiuczynski <fiuczy@linux.ibm.com>
Reviewed-by: Bjoern Walk <bwalk@linux.ibm.com>
Reviewed-by: Erik Skultety <eskultet@redhat.com>
2020-11-11 16:56:33 +01:00

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<h1>Host device management</h1>
<p>
Libvirt provides management of both physical and virtual host devices
(historically also referred to as node devices) like USB, PCI, SCSI, and
network devices. This also includes various virtualization capabilities
which the aforementioned devices provide for utilization, for example
SR-IOV, NPIV, MDEV, DRM, etc.
</p>
<p>
The node device driver provides means to list and show details about host
devices (<code>virsh nodedev-list</code>,
<code>virsh nodedev-dumpxml</code>), which are generic and can be used
with all devices. It also provides means to create and destroy devices
(<code>virsh nodedev-create</code>, <code>virsh nodedev-destroy</code>)
which are meant to be used to create virtual devices, currently only
supported by NPIV
(<a href="https://wiki.libvirt.org/page/NPIV_in_libvirt">more info about NPIV)</a>).
Devices on the host system are arranged in a tree-like hierarchy, with
the root node being called <code>computer</code>. The node device driver
supports udev backend (HAL backend was removed in <code>6.8.0</code>).
</p>
<p>
Details of the XML format of a host device can be found <a
href="formatnode.html">here</a>. Of particular interest is the
<code>capability</code> element, which describes features supported by
the device. Some specific device types are addressed in more detail
below.
</p>
<h2>Basic structure of a node device</h2>
<pre>
&lt;device&gt;
&lt;name&gt;pci_0000_00_17_0&lt;/name&gt;
&lt;path&gt;/sys/devices/pci0000:00/0000:00:17.0&lt;/path&gt;
&lt;parent&gt;computer&lt;/parent&gt;
&lt;driver&gt;
&lt;name&gt;ahci&lt;/name&gt;
&lt;/driver&gt;
&lt;capability type='pci'&gt;
...
&lt;/capability&gt;
&lt;/device&gt;</pre>
<ul id="toc"/>
<h2><a id="PCI">PCI host devices</a></h2>
<dl>
<dt><code>capability</code></dt>
<dd>
When used as top level element, the supported values for the
<code>type</code> attribute are <code>pci</code> and
<code>phys_function</code> (see <a href="#SRIOVCap">SR-IOV below</a>).
</dd>
</dl>
<pre>
&lt;device&gt;
&lt;name&gt;pci_0000_04_00_1&lt;/name&gt;
&lt;path&gt;/sys/devices/pci0000:00/0000:00:06.0/0000:04:00.1&lt;/path&gt;
&lt;parent&gt;pci_0000_00_06_0&lt;/parent&gt;
&lt;driver&gt;
&lt;name&gt;igb&lt;/name&gt;
&lt;/driver&gt;
&lt;capability type='pci'&gt;
&lt;domain&gt;0&lt;/domain&gt;
&lt;bus&gt;4&lt;/bus&gt;
&lt;slot&gt;0&lt;/slot&gt;
&lt;function&gt;1&lt;/function&gt;
&lt;product id='0x10c9'&gt;82576 Gigabit Network Connection&lt;/product&gt;
&lt;vendor id='0x8086'&gt;Intel Corporation&lt;/vendor&gt;
&lt;iommuGroup number='15'&gt;
&lt;address domain='0x0000' bus='0x04' slot='0x00' function='0x1'/&gt;
&lt;/iommuGroup&gt;
&lt;numa node='0'/&gt;
&lt;pci-express&gt;
&lt;link validity='cap' port='1' speed='2.5' width='2'/&gt;
&lt;link validity='sta' speed='2.5' width='2'/&gt;
&lt;/pci-express&gt;
&lt;/capability&gt;
&lt;/device&gt;</pre>
<p>
The XML format for a PCI device stays the same for any further
capabilities it supports, a single nested <code>&lt;capability&gt;</code>
element will be included for each capability the device supports.
</p>
<h3><a id="SRIOVCap">SR-IOV capability</a></h3>
<p>
Single root input/output virtualization (SR-IOV) allows sharing of the
PCIe resources by multiple virtual environments. That is achieved by
slicing up a single full-featured physical resource called physical
function (PF) into multiple devices called virtual functions (VFs) sharing
their configuration with the underlying PF. Despite the SR-IOV
specification, the amount of VFs that can be created on a PF varies among
manufacturers.
</p>
<p>
Suppose the NIC <a href="#PCI">above</a> was also SR-IOV capable, it would
also include a nested
<code>&lt;capability&gt;</code> element enumerating all virtual
functions available on the physical device (physical port) like in the
example below.
</p>
<pre>
&lt;capability type='pci'&gt;
...
&lt;capability type='virt_functions' maxCount='7'&gt;
&lt;address domain='0x0000' bus='0x04' slot='0x10' function='0x1'/&gt;
&lt;address domain='0x0000' bus='0x04' slot='0x10' function='0x3'/&gt;
&lt;address domain='0x0000' bus='0x04' slot='0x10' function='0x5'/&gt;
&lt;address domain='0x0000' bus='0x04' slot='0x10' function='0x7'/&gt;
&lt;address domain='0x0000' bus='0x04' slot='0x11' function='0x1'/&gt;
&lt;address domain='0x0000' bus='0x04' slot='0x11' function='0x3'/&gt;
&lt;address domain='0x0000' bus='0x04' slot='0x11' function='0x5'/&gt;
&lt;/capability&gt;
...
&lt;/capability&gt;</pre>
<p>
A SR-IOV child device on the other hand, would then report its top level
capability type as a <code>phys_function</code> instead:
</p>
<pre>
&lt;device&gt;
...
&lt;capability type='phys_function'&gt;
&lt;address domain='0x0000' bus='0x04' slot='0x00' function='0x0'/&gt;
&lt;/capability&gt;
...
&lt;/device&gt;</pre>
<h3><a id="MDEVCap">MDEV capability</a></h3>
<p>
A device capable of creating mediated devices will include a nested
capability <code>mdev_types</code> which enumerates all supported mdev
types on the physical device, along with the type attributes available
through sysfs. A detailed description of the XML format for the
<code>mdev_types</code> capability can be found
<a href="formatnode.html#MDEVTypesCap">here</a>.
</p>
<p>
The following example shows how we might represent an NVIDIA GPU device
that supports mediated devices. See below for <a href="#MDEV">more
information about mediated devices</a>.
</p>
<pre>
&lt;device&gt;
...
&lt;driver&gt;
&lt;name&gt;nvidia&lt;/name&gt;
&lt;/driver&gt;
&lt;capability type='pci'&gt;
...
&lt;capability type='mdev_types'&gt;
&lt;type id='nvidia-11'&gt;
&lt;name&gt;GRID M60-0B&lt;/name&gt;
&lt;deviceAPI&gt;vfio-pci&lt;/deviceAPI&gt;
&lt;availableInstances&gt;16&lt;/availableInstances&gt;
&lt;/type&gt;
&lt;!-- Here would come the rest of the available mdev types --&gt;
&lt;/capability&gt;
...
&lt;/capability&gt;
&lt;/device&gt;</pre>
<h2><a id="MDEV">Mediated devices (MDEVs)</a></h2>
<p>
Mediated devices (<span class="since">Since 3.2.0</span>) are software
devices defining resource allocation on the backing physical device which
in turn allows the parent physical device's resources to be divided into
several mediated devices, thus sharing the physical device's performance
among multiple guests. Unlike SR-IOV however, where a PCIe device appears
as multiple separate PCIe devices on the host's PCI bus, mediated devices
only appear on the mdev virtual bus. Therefore, no detach/reattach
procedure from/to the host driver procedure is involved even though
mediated devices are used in a direct device assignment manner. A
detailed description of the XML format for the <code>mdev</code>
capability can be found <a href="formatnode.html#mdev">here</a>.
</p>
<h3>Example of a mediated device</h3>
<pre>
&lt;device&gt;
&lt;name&gt;mdev_4b20d080_1b54_4048_85b3_a6a62d165c01&lt;/name&gt;
&lt;path&gt;/sys/devices/pci0000:00/0000:00:02.0/4b20d080-1b54-4048-85b3-a6a62d165c01&lt;/path&gt;
&lt;parent&gt;pci_0000_06_00_0&lt;/parent&gt;
&lt;driver&gt;
&lt;name&gt;vfio_mdev&lt;/name&gt;
&lt;/driver&gt;
&lt;capability type='mdev'&gt;
&lt;type id='nvidia-11'/&gt;
&lt;iommuGroup number='12'/&gt;
&lt;/capability&gt;
&lt;/device&gt;</pre>
<p>
The support of mediated device's framework in libvirt's node device driver
covers the following features:
</p>
<ul>
<li>
list available mediated devices on the host
(<span class="since">Since 3.4.0</span>)
</li>
<li>
display device details
(<span class="since">Since 3.4.0</span>)
</li>
</ul>
<p>
Because mediated devices are instantiated from vendor specific templates,
simply called 'types', information describing these types is contained
within the parent device's capabilities
(see the example in <a href="#PCI">PCI host devices</a>).
</p>
<p>
To see the supported mediated device types on a specific physical device
use the following:
</p>
<pre>
$ ls /sys/class/mdev_bus/&lt;device&gt;/mdev_supported_types</pre>
<p>
Before creating a mediated device, unbind the device from the respective
device driver, eg. subchannel I/O driver for a CCW device. Then bind the
device to the respective VFIO driver. For a CCW device, also unbind the
corresponding subchannel of the CCW device from the subchannel I/O driver
and then bind the subchannel (instead of the CCW device) to the vfio_ccw
driver. The below example shows the unbinding and binding steps for a CCW
device.
</p>
<pre>
device="0.0.1234"
subchannel="0.0.0123"
echo $device &gt; /sys/bus/ccw/devices/$device/driver/unbind
echo $subchannel &gt; /sys/bus/css/devices/$subchannel/driver/unbind
echo $subchannel &gt; /sys/bus/css/drivers/vfio_ccw/bind
</pre>
<p>
To manually instantiate a mediated device, use one of the following as a
reference. For a CCW device, use the subchannel ID instead of the device
ID.
</p>
<pre>
$ uuidgen &gt; /sys/class/mdev_bus/&lt;device&gt;/mdev_supported_types/&lt;type&gt;/create
...
$ echo &lt;UUID&gt; &gt; /sys/class/mdev_bus/&lt;device&gt;/mdev_supported_types/&lt;type&gt;/create</pre>
<p>
Manual removal of a mediated device is then performed as follows:
</p>
<pre>
$ echo 1 &gt; /sys/bus/mdev/devices/&lt;uuid&gt;/remove</pre>
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