mirror of
https://gitlab.com/libvirt/libvirt.git
synced 2024-12-22 17:34:18 +03:00
73713a54a8
We support pcie-to-pci-bridge, and prefer it to dmi-to-pci-bridge, since libvirt 4.3.0, but we didn't update all the documentation accordingly at the time. Signed-off-by: Andrea Bolognani <abologna@redhat.com> Reviewed-by: Ján Tomko <jtomko@redhat.com>
186 lines
6.5 KiB
XML
186 lines
6.5 KiB
XML
<?xml version="1.0" encoding="UTF-8"?>
|
|
<!DOCTYPE html>
|
|
<html xmlns="http://www.w3.org/1999/xhtml">
|
|
<body>
|
|
<h1>PCI topology and hotplug</h1>
|
|
|
|
<ul id="toc"></ul>
|
|
|
|
<p>
|
|
Perhaps surprisingly, most libvirt guests support only limited PCI
|
|
device hotplug out of the box, or even none at all.
|
|
</p>
|
|
<p>
|
|
The reason for this apparent limitation is the fact that each
|
|
hotplugged PCI device might require additional PCI controllers to
|
|
be added to the guest. Since most PCI controllers can't be
|
|
hotplugged, they need to be added before the guest is started;
|
|
however, libvirt has no way of knowing in advance how many devices
|
|
will be hotplugged during the guest's lifetime, thus making it
|
|
impossible to automatically provide the right amount of PCI
|
|
controllers: any arbitrary number would end up being too big
|
|
for some users, and too small for others.
|
|
</p>
|
|
<p>
|
|
Ultimately, the user is the only one who knows how much the guest
|
|
will need to grow dynamically, so the responsibility of planning
|
|
a suitable PCI topology in advance falls on them.
|
|
</p>
|
|
<p>
|
|
This document aims at providing all the information needed to
|
|
successfully plan the PCI topology of a guest. Note that the
|
|
details can vary a lot between architectures and even machine
|
|
types, hence the way it's organized.
|
|
</p>
|
|
|
|
<h2><a id="x86_64">x86_64 architecture</a></h2>
|
|
|
|
<h3><a id="x86_64-q35">q35 machine type</a></h3>
|
|
|
|
<p>
|
|
This is a PCI Express native machine type. The default PCI topology
|
|
looks like
|
|
</p>
|
|
|
|
<pre>
|
|
<controller type='pci' index='0' model='pcie-root'/>
|
|
<controller type='pci' index='1' model='pcie-root-port'>
|
|
<model name='pcie-root-port'/>
|
|
<target chassis='1' port='0x10'/>
|
|
<address type='pci' domain='0x0000' bus='0x00' slot='0x01' function='0x0'/>
|
|
</controller></pre>
|
|
|
|
<p>
|
|
and supports hotplugging a single PCI Express device, either
|
|
emulated or assigned from the host.
|
|
</p>
|
|
<p>
|
|
If you have a very specific use case, such as the appliances
|
|
used by <a href="http://libguestfs.org/">libguestfs</a> behind
|
|
the scenes to access disk images, and this automatically-added
|
|
<code>pcie-root-port</code> controller ends up being a nuisance,
|
|
you can prevent libvirt from adding it by manually managing PCI
|
|
controllers and addresses according to your needs.
|
|
</p>
|
|
<p>
|
|
Slots on the <code>pcie-root</code> controller do not support
|
|
hotplug, so the device will be hotplugged into the
|
|
<code>pcie-root-port</code> controller. If you plan to hotplug
|
|
more than a single PCI Express device, you should add a suitable
|
|
number of <code>pcie-root-port</code> controllers when defining
|
|
the guest: for example, add
|
|
</p>
|
|
|
|
<pre>
|
|
<controller type='pci' model='pcie-root'/>
|
|
<controller type='pci' model='pcie-root-port'/>
|
|
<controller type='pci' model='pcie-root-port'/>
|
|
<controller type='pci' model='pcie-root-port'/></pre>
|
|
|
|
<p>
|
|
if you expect to hotplug up to three PCI Express devices,
|
|
either emulated or assigned from the host. That's all the
|
|
information you need to provide: libvirt will fill in the
|
|
remaining details automatically. Note that you need to add
|
|
the <code>pcie-root</code> controller along with the
|
|
<code>pcie-root-port</code> controllers or you will get an
|
|
error.
|
|
</p>
|
|
<p>
|
|
Note that if you're adding PCI controllers to a guest and at
|
|
the same time you're also adding PCI devices, some of the
|
|
controllers will be used for the newly-added devices and won't
|
|
be available for hotplug once the guest has been started.
|
|
</p>
|
|
<p>
|
|
If you expect to hotplug legacy PCI devices, then you will need
|
|
specialized controllers, since all those mentioned above are
|
|
intended for PCI Express devices only: add
|
|
</p>
|
|
|
|
<pre>
|
|
<controller type='pci' model='pcie-to-pci-bridge'/></pre>
|
|
|
|
<p>
|
|
and you'll be able to hotplug up to 31 legacy PCI devices,
|
|
either emulated or assigned from the host, in the slots
|
|
from 0x01 to 0x1f of the <code>pcie-to-pci-bridge</code> controller.
|
|
</p>
|
|
|
|
<h3><a id="x86_64-i440fx">i440fx (pc) machine type</a></h3>
|
|
|
|
<p>
|
|
This is a legacy PCI native machine type. The default PCI
|
|
topology looks like
|
|
</p>
|
|
|
|
<pre>
|
|
<controller type='pci' index='0' model='pci-root'/></pre>
|
|
|
|
<p>
|
|
where each of the 31 slots (from 0x01 to 0x1f) on the
|
|
<code>pci-root</code> controller is hotplug capable and
|
|
can accept a legacy PCI device, either emulated or
|
|
assigned from the guest.
|
|
</p>
|
|
|
|
<h2><a id="ppc64">ppc64 architecture</a></h2>
|
|
|
|
<h3><a id="ppc64-pseries">pseries machine type</a></h3>
|
|
|
|
<p>
|
|
The default PCI topology for the <code>pseries</code> machine
|
|
type looks like
|
|
</p>
|
|
|
|
<pre>
|
|
<controller type='pci' index='0' model='pci-root'>
|
|
<model name='spapr-pci-host-bridge'/>
|
|
<target index='0'/>
|
|
</controller></pre>
|
|
|
|
<p>
|
|
The 31 slots, from 0x01 to 0x1f, on a <code>pci-root</code>
|
|
controller are all hotplug capable and, despite the name
|
|
suggesting otherwise, starting with QEMU 2.9 all of them
|
|
can accept PCI Express devices in addition to legacy PCI
|
|
devices; however, libvirt will only place emulated devices
|
|
on the default <code>pci-root</code> controller.
|
|
</p>
|
|
<p>
|
|
In order to take advantage of improved error reporting and
|
|
recovering capabilities, PCI devices assigned from the
|
|
host need to be isolated by placing each on a separate
|
|
<code>pci-root</code> controller, which has to be prepared
|
|
in advance for hotplug to work: for example, add
|
|
</p>
|
|
|
|
<pre>
|
|
<controller type='pci' model='pci-root'/>
|
|
<controller type='pci' model='pci-root'/>
|
|
<controller type='pci' model='pci-root'/></pre>
|
|
|
|
<p>
|
|
if you expect to hotplug up to three PCI devices assigned
|
|
from the host.
|
|
</p>
|
|
|
|
<h2><a id="aarch64">aarch64 architecture</a></h2>
|
|
|
|
<h3><a id="aarch64-virt">mach-virt (virt) machine type</a></h3>
|
|
|
|
<p>
|
|
This machine type mostly behaves the same as the
|
|
<a href="#x86_64-q35">q35 machine type</a>, so you can just
|
|
refer to that section for information.
|
|
</p>
|
|
<p>
|
|
The only difference worth mentioning is that using legacy
|
|
PCI for <code>mach-virt</code> guests is extremely uncommon,
|
|
so you'll probably never need to add controllers other than
|
|
<code>pcie-root-port</code>.
|
|
</p>
|
|
|
|
</body>
|
|
</html>
|