Chapter 13. Managing GPU devices in virtual machines To enhance the graphical performance of your virtual machine (VMs) on a RHEL 8 host, you can assign a host GPU to a VM. You can detach the GPU from the host and pass full control of the GPU directly to the VM. You can create multiple mediated devices from a physical GPU, and assign these devices as virtual GPUs (vGPUs) to multiple guests. This is currently only supported on selected NVIDIA GPUs, and only one mediated device can be assigned to a single guest. Important GPU assignment is currently only supported on Intel 64 and AMD64 systems. 13.1. Assigning a GPU to a virtual machine To access and control GPUs that are attached to the host system, you must configure the host system to pass direct control of the GPU to the virtual machine (VM). Note If you are looking for information about assigning a virtual GPU, see Managing NVIDIA vGPU devices . Prerequisites You must enable IOMMU support on the host machine kernel. On an Intel host, you must enable VT-d: Regenerate the GRUB configuration with the intel_iommu=on and iommu=pt parameters: Reboot the host. On an AMD host, you must enable AMD-Vi. Note that on AMD hosts, IOMMU is enabled by default, you can add iommu=pt to switch it to pass-through mode: Regenerate the GRUB configuration with the iommu=pt parameter: Note The pt option only enables IOMMU for devices used in pass-through mode and provides better host performance. However, not all hardware supports the option. You can still assign devices even when this option is not enabled. Reboot the host. Procedure Prevent the driver from binding to the GPU. Identify the PCI bus address to which the GPU is attached. Prevent the host's graphics driver from using the GPU. To do so, use the GPU PCI ID with the pci-stub driver. For example, the following command prevents the driver from binding to the GPU attached at the 10de:11fa bus: Reboot the host. Optional: If certain GPU functions, such as audio, cannot be passed through to the VM due to support limitations, you can modify the driver bindings of the endpoints within an IOMMU group to pass through only the necessary GPU functions. Convert the GPU settings to XML and note the PCI address of the endpoints that you want to prevent from attaching to the host drivers. To do so, convert the GPU's PCI bus address to a libvirt-compatible format by adding the pci_ prefix to the address, and converting the delimiters to underscores. For example, the following command displays the XML configuration of the GPU attached at the 0000:02:00.0 bus address. <device> <name>pci_0000_02_00_0</name> <path>/sys/devices/pci0000:00/0000:00:03.0/0000:02:00.0</path> <parent>pci_0000_00_03_0</parent> <driver> <name>pci-stub</name> </driver> <capability type='pci'> <domain>0</domain> <bus>2</bus> <slot>0</slot> <function>0</function> <product id='0x11fa'>GK106GL [Quadro K4000]</product> <vendor id='0x10de'>NVIDIA Corporation</vendor> <iommuGroup number='13'> <address domain='0x0000' bus='0x02' slot='0x00' function='0x0'/> <address domain='0x0000' bus='0x02' slot='0x00' function='0x1'/> </iommuGroup> <pci-express> <link validity='cap' port='0' speed='8' width='16'/> <link validity='sta' speed='2.5' width='16'/> </pci-express> </capability> </device> Prevent the endpoints from attaching to the host driver. In this example, to assign the GPU to a VM, prevent the endpoints that correspond to the audio function, <address domain='0x0000' bus='0x02' slot='0x00' function='0x1'/> , from attaching to the host audio driver, and instead attach the endpoints to VFIO-PCI. Attach the GPU to the VM Create an XML configuration file for the GPU by using the PCI bus address. For example, you can create the following XML file, GPU-Assign.xml, by using parameters from the GPU's bus address. <hostdev mode='subsystem' type='pci' managed='yes'> <driver name='vfio'/> <source> <address domain='0x0000' bus='0x02' slot='0x00' function='0x0'/> </source> </hostdev> Save the file on the host system. Merge the file with the VM's XML configuration. For example, the following command merges the GPU XML file, GPU-Assign.xml, with the XML configuration file of the System1 VM. Note The GPU is attached as a secondary graphics device to the VM. Assigning a GPU as the primary graphics device is not supported, and Red Hat does not recommend removing the primary emulated graphics device in the VM's XML configuration. Verification The device appears under the <devices> section in VM's XML configuration. For more information, see Sample virtual machine XML configuration . Known Issues The number of GPUs that can be attached to a VM is limited by the maximum number of assigned PCI devices, which in RHEL 8 is currently 64. However, attaching multiple GPUs to a VM is likely to cause problems with memory-mapped I/O (MMIO) on the guest, which may result in the GPUs not being available to the VM. To work around these problems, set a larger 64-bit MMIO space and configure the vCPU physical address bits to make the extended 64-bit MMIO space addressable. Attaching an NVIDIA GPU device to a VM that uses a RHEL 8 guest operating system currently disables the Wayland session on that VM, and loads an Xorg session instead. This is because of incompatibilities between NVIDIA drivers and Wayland. 13.2. Managing NVIDIA vGPU devices The vGPU feature makes it possible to divide a physical NVIDIA GPU device into multiple virtual devices, referred to as mediated devices . These mediated devices can then be assigned to multiple virtual machines (VMs) as virtual GPUs. As a result, these VMs can share the performance of a single physical GPU. Important Assigning a physical GPU to VMs, with or without using mediated devices, makes it impossible for the host to use the GPU. 13.2.1. Setting up NVIDIA vGPU devices To set up the NVIDIA vGPU feature, you need to download NVIDIA vGPU drivers for your GPU device, create mediated devices, and assign them to the intended virtual machines. For detailed instructions, see below. Prerequisites Your GPU supports vGPU mediated devices. For an up-to-date list of NVIDIA GPUs that support creating vGPUs, see the NVIDIA vGPU software documentation . If you do not know which GPU your host is using, install the lshw package and use the lshw -C display command. The following example shows the system is using an NVIDIA Tesla P4 GPU, compatible with vGPU. Procedure Download the NVIDIA vGPU drivers and install them on your system. For instructions, see the NVIDIA documentation . If the NVIDIA software installer did not create the /etc/modprobe.d/nvidia-installer-disable-nouveau.conf file, create a conf file of any name in /etc/modprobe.d/ , and add the following lines in the file: Regenerate the initial ramdisk for the current kernel, then reboot. Check that the kernel has loaded the nvidia_vgpu_vfio module and that the nvidia-vgpu-mgr.service service is running. In addition, if creating vGPU based on an NVIDIA Ampere GPU device, ensure that virtual functions are enable for the physical GPU. For instructions, see the NVIDIA documentation . Generate a device UUID. Prepare an XML file with a configuration of the mediated device, based on the detected GPU hardware. For example, the following configures a mediated device of the nvidia-63 vGPU type on an NVIDIA Tesla P4 card that runs on the 0000:01:00.0 PCI bus and uses the UUID generated in the step. <device> <parent>pci_0000_01_00_0</parent> <capability type="mdev"> <type id="nvidia-63"/> <uuid>30820a6f-b1a5-4503-91ca-0c10ba58692a</uuid> </capability> </device> Define a vGPU mediated device based on the XML file you prepared. For example: Optional: Verify that the mediated device is listed as inactive. Start the vGPU mediated device you created. Optional: Ensure that the mediated device is listed as active. Set the vGPU device to start automatically after the host reboots Attach the mediated device to a VM that you want to share the vGPU resources. To do so, add the following lines, along with the previously genereated UUID, to the <devices/> sections in the XML configuration of the VM. <hostdev mode='subsystem' type='mdev' managed='no' model='vfio-pci' display='on'> <source> <address uuid='30820a6f-b1a5-4503-91ca-0c10ba58692a'/> </source> </hostdev> Note that each UUID can only be assigned to one VM at a time. In addition, if the VM does not have QEMU video devices, such as virtio-vga , add also the ramfb='on' parameter on the <hostdev> line. For full functionality of the vGPU mediated devices to be available on the assigned VMs, set up NVIDIA vGPU guest software licensing on the VMs. For further information and instructions, see the NVIDIA Virtual GPU Software License Server User Guide . Verification Query the capabilities of the vGPU you created, and ensure it is listed as active and persistent. Start the VM and verify that the guest operating system detects the mediated device as an NVIDIA GPU. For example, if the VM uses Linux: Known Issues Assigning an NVIDIA vGPU mediated device to a VM that uses a RHEL 8 guest operating system currently disables the Wayland session on that VM, and loads an Xorg session instead. This is because of incompatibilities between NVIDIA drivers and Wayland. Additional resources NVIDIA vGPU software documentation The man virsh command 13.2.2. Removing NVIDIA vGPU devices To change the configuration of assigned vGPU mediated devices , you need to remove the existing devices from the assigned VMs. For instructions, see below: Prerequisites The VM from which you want to remove the device is shut down. Procedure Obtain the ID of the mediated device that you want to remove. Stop the running instance of the vGPU mediated device. Optional: Ensure the mediated device has been deactivated. Remove the device from the XML configuration of the VM. To do so, use the virsh edit utility to edit the XML configuration of the VM, and remove the mdev's configuration segment. The segment will look similar to the following: <hostdev mode='subsystem' type='mdev' managed='no' model='vfio-pci'> <source> <address uuid='30820a6f-b1a5-4503-91ca-0c10ba58692a'/> </source> </hostdev> Note that stopping and detaching the mediated device does not delete it, but rather keeps it as defined . As such, you can restart and attach the device to a different VM. Optional: To delete the stopped mediated device, remove its definition. Verification If you only stopped and detached the device, ensure the mediated device is listed as inactive. If you also deleted the device, ensure the following command does not display it. Additional resources The man virsh command 13.2.3. Obtaining NVIDIA vGPU information about your system To evaluate the capabilities of the vGPU features available to you, you can obtain additional information about the mediated devices on your system, such as: How many mediated devices of a given type can be created What mediated devices are already configured on your system. Procedure To see the available GPUs devices on your host that can support vGPU mediated devices, use the virsh nodedev-list --cap mdev_types command. For example, the following shows a system with two NVIDIA Quadro RTX6000 devices. To display vGPU types supported by a specific GPU device, as well as additional metadata, use the virsh nodedev-dumpxml command. Additional resources The man virsh command 13.2.4. Remote desktop streaming services for NVIDIA vGPU The following remote desktop streaming services are supported on the RHEL 8 hypervisor with NVIDIA vGPU or NVIDIA GPU passthrough enabled: HP ZCentral Remote Boost/Teradici NICE DCV Mechdyne TGX For support details, see the appropriate vendor support matrix. 13.2.5. Additional resources NVIDIA vGPU software documentation

Commands:
grubby --args="intel_iommu=on iommu_pt" --update-kernel DEFAULT
grubby --args="iommu=pt" --update-kernel DEFAULT
lspci -Dnn | grep VGA 0000:02:00.0 VGA compatible controller [0300]: NVIDIA Corporation GK106GL [Quadro K4000] [ 10de:11fa ] (rev a1)
grubby --args="pci-stub.ids=10de:11fa" --update-kernel DEFAULT
virsh nodedev-dumpxml pci_0000_02_00_0
<device> <name>pci_0000_02_00_0</name> <path>/sys/devices/pci0000:00/0000:00:03.0/0000:02:00.0</path> <parent>pci_0000_00_03_0</parent> <driver> <name>pci-stub</name> </driver> <capability type='pci'> <domain>0</domain> <bus>2</bus> <slot>0</slot> <function>0</function> <product id='0x11fa'>GK106GL [Quadro K4000]</product> <vendor id='0x10de'>NVIDIA Corporation</vendor> <iommuGroup number='13'> <address domain='0x0000' bus='0x02' slot='0x00' function='0x0'/> <address domain='0x0000' bus='0x02' slot='0x00' function='0x1'/> </iommuGroup> <pci-express> <link validity='cap' port='0' speed='8' width='16'/> <link validity='sta' speed='2.5' width='16'/> </pci-express> </capability> </device>
driverctl set-override 0000:02:00.1 vfio-pci
<hostdev mode='subsystem' type='pci' managed='yes'> <driver name='vfio'/> <source> <address domain='0x0000' bus='0x02' slot='0x00' function='0x0'/> </source> </hostdev>
virsh attach-device System1 --file /home/GPU-Assign.xml --persistent Device attached successfully.
lshw -C display *-display description: 3D controller product: GP104GL [Tesla P4] vendor: NVIDIA Corporation physical id: 0 bus info: pci@0000:01:00.0 version: a1 width: 64 bits clock: 33MHz capabilities: pm msi pciexpress cap_list configuration: driver=vfio-pci latency=0 resources: irq:16 memory:f6000000-f6ffffff memory:e0000000-efffffff memory:f0000000-f1ffffff
blacklist nouveau options nouveau modeset=0
dracut --force reboot
lsmod | grep nvidia_vgpu_vfio nvidia_vgpu_vfio 45011 0 nvidia 14333621 10 nvidia_vgpu_vfio mdev 20414 2 vfio_mdev,nvidia_vgpu_vfio vfio 32695 3 vfio_mdev,nvidia_vgpu_vfio,vfio_iommu_type1 systemctl status nvidia-vgpu-mgr.service nvidia-vgpu-mgr.service - NVIDIA vGPU Manager Daemon Loaded: loaded (/usr/lib/systemd/system/nvidia-vgpu-mgr.service; enabled; vendor preset: disabled) Active: active (running) since Fri 2018-03-16 10:17:36 CET; 5h 8min ago Main PID: 1553 (nvidia-vgpu-mgr) [...]
uuidgen 30820a6f-b1a5-4503-91ca-0c10ba58692a
<device> <parent>pci_0000_01_00_0</parent> <capability type="mdev"> <type id="nvidia-63"/> <uuid>30820a6f-b1a5-4503-91ca-0c10ba58692a</uuid> </capability> </device>
virsh nodedev-define vgpu-test.xml Node device mdev_30820a6f_b1a5_4503_91ca_0c10ba58692a_0000_01_00_0 created from vgpu-test.xml
virsh nodedev-list --cap mdev --inactive mdev_30820a6f_b1a5_4503_91ca_0c10ba58692a_0000_01_00_0
virsh nodedev-start mdev_30820a6f_b1a5_4503_91ca_0c10ba58692a_0000_01_00_0 Device mdev_30820a6f_b1a5_4503_91ca_0c10ba58692a_0000_01_00_0 started
virsh nodedev-list --cap mdev mdev_30820a6f_b1a5_4503_91ca_0c10ba58692a_0000_01_00_0
virsh nodedev-autostart mdev_30820a6f_b1a5_4503_91ca_0c10ba58692a_0000_01_00_0 Device mdev_d196754e_d8ed_4f43_bf22_684ed698b08b_0000_9b_00_0 marked as autostarted
<hostdev mode='subsystem' type='mdev' managed='no' model='vfio-pci' display='on'> <source> <address uuid='30820a6f-b1a5-4503-91ca-0c10ba58692a'/> </source> </hostdev>
virsh nodedev-info mdev_30820a6f_b1a5_4503_91ca_0c10ba58692a_0000_01_00_0 Name: virsh nodedev-autostart mdev_30820a6f_b1a5_4503_91ca_0c10ba58692a_0000_01_00_0 Parent: pci_0000_01_00_0 Active: yes Persistent: yes Autostart: yes
lspci -d 10de: -k 07:00.0 VGA compatible controller: NVIDIA Corporation GV100GL [Tesla V100 SXM2 32GB] (rev a1) Subsystem: NVIDIA Corporation Device 12ce Kernel driver in use: nvidia Kernel modules: nouveau, nvidia_drm, nvidia
virsh nodedev-list --cap mdev mdev_30820a6f_b1a5_4503_91ca_0c10ba58692a_0000_01_00_0
virsh nodedev-destroy mdev_30820a6f_b1a5_4503_91ca_0c10ba58692a_0000_01_00_0 Destroyed node device 'mdev_30820a6f_b1a5_4503_91ca_0c10ba58692a_0000_01_00_0'
virsh nodedev-info mdev_30820a6f_b1a5_4503_91ca_0c10ba58692a_0000_01_00_0 Name: virsh nodedev-autostart mdev_30820a6f_b1a5_4503_91ca_0c10ba58692a_0000_01_00_0 Parent: pci_0000_01_00_0 Active: no Persistent: yes Autostart: yes
<hostdev mode='subsystem' type='mdev' managed='no' model='vfio-pci'> <source> <address uuid='30820a6f-b1a5-4503-91ca-0c10ba58692a'/> </source> </hostdev>
virsh nodedev-undefine mdev_30820a6f_b1a5_4503_91ca_0c10ba58692a_0000_01_00_0 Undefined node device 'mdev_30820a6f_b1a5_4503_91ca_0c10ba58692a_0000_01_00_0'
virsh nodedev-list --cap mdev --inactive mdev_30820a6f_b1a5_4503_91ca_0c10ba58692a_0000_01_00_0
virsh nodedev-list --cap mdev
virsh nodedev-list --cap mdev_types pci_0000_5b_00_0 pci_0000_9b_00_0
virsh nodedev-dumpxml pci_0000_9b_00_0 <device> <name>pci_0000_9b_00_0</name> <path>/sys/devices/pci0000:9a/0000:9a:00.0/0000:9b:00.0</path> <parent>pci_0000_9a_00_0</parent> <driver> <name>nvidia</name> </driver> <capability type='pci'> <class>0x030000</class> <domain>0</domain> <bus>155</bus> <slot>0</slot> <function>0</function> <product id='0x1e30'>TU102GL [Quadro RTX 6000/8000]</product> <vendor id='0x10de'>NVIDIA Corporation</vendor> <capability type='mdev_types'> <type id='nvidia-346'> <name>GRID RTX6000-12C</name> <deviceAPI>vfio-pci</deviceAPI> <availableInstances>2</availableInstances> </type> <type id='nvidia-439'> <name>GRID RTX6000-3A</name> <deviceAPI>vfio-pci</deviceAPI> <availableInstances>8</availableInstances> </type> [...] <type id='nvidia-440'> <name>GRID RTX6000-4A</name> <deviceAPI>vfio-pci</deviceAPI> <availableInstances>6</availableInstances> </type> <type id='nvidia-261'> <name>GRID RTX6000-8Q</name> <deviceAPI>vfio-pci</deviceAPI> <availableInstances>3</availableInstances> </type> </capability> <iommuGroup number='216'> <address domain='0x0000' bus='0x9b' slot='0x00' function='0x3'/> <address domain='0x0000' bus='0x9b' slot='0x00' function='0x1'/> <address domain='0x0000' bus='0x9b' slot='0x00' function='0x2'/> <address domain='0x0000' bus='0x9b' slot='0x00' function='0x0'/> </iommuGroup> <numa node='2'/> <pci-express> <link validity='cap' port='0' speed='8' width='16'/> <link validity='sta' speed='2.5' width='8'/> </pci-express> </capability> </device>