PCI passthrough should be safe by default, but non-default options may be required. Please make sure you carefully read and understand the **[security considerations]** before deviating from default behavior.
Unlike other devices ([USB], [block], mic), PCI devices need to be attached on VM-bootup. Similar to how you can't attach a new sound-card after your computer booted (and expect it to work properly), attaching PCI devices to already booted VMs isn't supported.
The Qubes installer attaches all network class controllers to `sys-net` and all USB controllers to `sys-usb` by default, if you chose to create the network and USB qube during install.
While this covers most use cases, there are some occasions when you may want to manually attach one NIC to `sys-net` and another to a custom NetVM, or have some other type of PCI controller you want to manually attach.
Some devices expose multiple functions with distinct BDF-numbers. Limits imposed by the PC and VT-d architectures may require all functions belonging to the same device to be attached to the same VM. This requirement can be dropped with the `no-strict-reset` option during attachment, bearing in mind the aforementioned [security considerations].
In the steps below, you can tell if this is needed if you see the BDF for the same device listed multiple times with only the number after the "." changing.
While PCI device can only be used by one powered on VM at a time, it *is* possible to *assign* the same device to more than one VM at a time.
This means that you can use the device in one VM, shut that VM down, start up a different VM (to which the same device is now attached), then use the device in that VM.
This can be useful if, for example, you have only one USB controller, but you have multiple security domains which all require the use of different USB devices.
The qube settings for a VM offers the "Devices"-tab. There you can attach PCI-devices to a qube.
1. To reach the settings of any qube either
- Press Alt+F3 to open the application finder, type in the VM name, select the "![appmenu]\[VM-name\]: Qube Settings" menu entry and press enter or click "Launch"!
- Select the VM in Qube Manager and click the settings-button or right-click the VM and select `Qube settings`.
- Click the Domain Manager ![device manager icon], hover the VM you want to attach a device to and select "settings" in the additional menu. (only running VMs!)
5. In case it doesn't work out, first try disabling memory-balancing in the settings ("Advanced" tab). If that doesn't help, read on to learn how to disable the strict reset requirement!
Attaching a PCI device through the commandline offers additional options, specifiable via the `--option`/`-o` option. (Yes, confusing wording, there's an [issue for that](https://github.com/QubesOS/qubes-issues/issues/4530).)
`qvm-pci` exposes two additional options. Both are intended to fix device or driver specific issues, but both come with [heavy security implications][security considerations]! **Make sure you understand them before continuing!**
By default, when a device is detached from a VM (or when a VM with an attached PCI device is shut down), the device is *not* automatically attached back to dom0.
A device which was previously attached to a VM less trusted than dom0 (which, in Qubes, is *all* of them) could attack dom0 if it were automatically reattached there.
