5 PCI(e) passthrough is a mechanism to give a virtual machine control over
6 a PCI device from the host. This can have some advantages over using
7 virtualized hardware, for example lower latency, higher performance, or more
8 features (e.g., offloading).
10 But, if you pass through a device to a virtual machine, you cannot use that
11 device anymore on the host or in any other VM.
16 Since passthrough is a feature which also needs hardware support, there are
17 some requirements to check and preparations to be done to make it work.
22 Your hardware needs to support `IOMMU` (*I*/*O* **M**emory **M**anagement
23 **U**nit) interrupt remapping, this includes the CPU and the mainboard.
25 Generally, Intel systems with VT-d, and AMD systems with AMD-Vi support this.
26 But it is not guaranteed that everything will work out of the box, due
27 to bad hardware implementation and missing or low quality drivers.
29 Further, server grade hardware has often better support than consumer grade
30 hardware, but even then, many modern system can support this.
32 Please refer to your hardware vendor to check if they support this feature
33 under Linux for your specific setup
39 Once you ensured that your hardware supports passthrough, you will need to do
40 some configuration to enable PCI(e) passthrough.
45 The IOMMU has to be activated on the kernel commandline. The easiest way is to
46 enable trough grub. Edit `'/etc/default/grub'' and add the following to the
47 'GRUB_CMDLINE_LINUX_DEFAULT' variable:
60 [[qm_pci_passthrough_update_grub]]
61 To bring this change in effect, make sure you run:
69 You have to make sure the following modules are loaded. This can be achieved by
70 adding them to `'/etc/modules''
79 [[qm_pci_passthrough_update_initramfs]]
80 After changing anything modules related, you need to refresh your
81 `initramfs`. On {pve} this can be done by executing:
84 # update-initramfs -u -k all
89 Finally reboot to bring the changes into effect and check that it is indeed
93 # dmesg -e DMAR -e IOMMU -e AMD-Vi
96 should display that `IOMMU`, `Directed I/O` or `Interrupt Remapping` is
97 enabled, depending on hardware and kernel the exact message can vary.
99 It is also important that the device(s) you want to pass through
100 are in a *separate* `IOMMU` group. This can be checked with:
103 # find /sys/kernel/iommu_groups/ -type l
106 It is okay if the device is in an `IOMMU` group together with its functions
107 (e.g. a GPU with the HDMI Audio device) or with its root port or PCI(e) bridge.
112 Some platforms handle their physical PCI(e) slots differently. So, sometimes
113 it can help to put the card in a another PCI(e) slot, if you do not get the
114 desired `IOMMU` group separation.
120 For some platforms, it may be necessary to allow unsafe interrupts.
121 For this add the following line in a file ending with `.conf' file in
125 options vfio_iommu_type1 allow_unsafe_interrupts=1
128 Please be aware that this option can make your system unstable.
131 Host Device Passthrough
132 ~~~~~~~~~~~~~~~~~~~~~~~
134 The most used variant of PCI(e) passthrough is to pass through a whole
135 PCI(e) card, for example a GPU or a network card.
141 In this case, the host cannot use the card. There are two methods to achieve
144 * pass the device IDs to the options of the 'vfio-pci' modules by adding
147 options vfio-pci ids=1234:5678,4321:8765
150 to a .conf file in */etc/modprobe.d/* where `1234:5678` and `4321:8765` are
151 the vendor and device IDs obtained by:
157 * blacklist the driver completely on the host, ensuring that it is free to bind
158 for passthrough, with
164 in a .conf file in */etc/modprobe.d/*.
166 For both methods you need to
167 xref:qm_pci_passthrough_update_initramfs[update the `initramfs`] again and
170 [[qm_pci_passthrough_vm_config]]
173 To pass through the device you need to set the *hostpciX* option in the VM
174 configuration, for example by executing:
177 # qm set VMID -hostpci0 00:02.0
180 If your device has multiple functions, you can pass them through all together
181 with the shortened syntax ``00:02`'
183 There are some options to which may be necessary, depending on the device
186 * *x-vga=on|off* marks the PCI(e) device as the primary GPU of the VM.
187 With this enabled the *vga* configuration option will be ignored.
189 * *pcie=on|off* tells {pve} to use a PCIe or PCI port. Some guests/device
190 combination require PCIe rather than PCI. PCIe is only available for 'q35'
193 * *rombar=on|off* makes the firmware ROM visible for the guest. Default is on.
194 Some PCI(e) devices need this disabled.
196 * *romfile=<path>*, is an optional path to a ROM file for the device to use.
197 This is a relative path under */usr/share/kvm/*.
201 An example of PCIe passthrough with a GPU set to primary:
204 # qm set VMID -hostpci0 02:00,pcie=on,x-vga=on
211 When passing through a GPU, the best compatibility is reached when using
212 'q35' as machine type, 'OVMF' ('EFI' for VMs) instead of SeaBIOS and PCIe
213 instead of PCI. Note that if you want to use 'OVMF' for GPU passthrough, the
214 GPU needs to have an EFI capable ROM, otherwise use SeaBIOS instead.
219 Another variant for passing through PCI(e) devices, is to use the hardware
220 virtualization features of your devices, if available.
222 'SR-IOV' (**S**ingle-**R**oot **I**nput/**O**utput **V**irtualization) enables
223 a single device to provide multiple 'VF' (**V**irtual **F**unctions) to the
224 system. Each of those 'VF' can be used in a different VM, with full hardware
225 features and also better performance and lower latency than software
228 Currently, the most common use case for this are NICs (**N**etwork
229 **I**nterface **C**ard) with SR-IOV support, which can provide multiple VFs per
230 physical port. This allows using features such as checksum offloading, etc. to
231 be used inside a VM, reducing the (host) CPU overhead.
237 Generally, there are two methods for enabling virtual functions on a device.
239 * sometimes there is an option for the driver module e.g. for some
246 which could be put file with '.conf' ending under */etc/modprobe.d/*.
247 (Do not forget to update your initramfs after that)
249 Please refer to your driver module documentation for the exact
250 parameters and options.
252 * The second, more generic, approach is using the `sysfs`.
253 If a device and driver supports this you can change the number of VFs on
254 the fly. For example, to setup 4 VFs on device 0000:01:00.0 execute:
257 # echo 4 > /sys/bus/pci/devices/0000:01:00.0/sriov_numvfs
260 To make this change persistent you can use the `sysfsutils` Debian package.
261 After installation configure it via */etc/sysfs.conf* or a `FILE.conf' in
267 After creating VFs, you should see them as separate PCI(e) devices when
268 outputting them with `lspci`. Get their ID and pass them through like a
269 xref:qm_pci_passthrough_vm_config[normal PCI(e) device].
274 For this feature, platform support is especially important. It may be necessary
275 to enable this feature in the BIOS/EFI first, or to use a specific PCI(e) port
276 for it to work. In doubt, consult the manual of the platform or contact its