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Virtual Function I/O Mediated devices (vfio-mdev) Create and Configure Virtual Function I/O Mediated devices (vfio-mdev) true 2023-01-29T20:12:01.722Z markdown 2022-07-21T21:10:41.046Z

Configure Virtual Function I/O Mediated devices

These instructions only cover Intel GPUs that are compatible with vfio-mdev (5th to 10th generation). Since generation 11th, vfio-mdev has been superseded by SR-IOV. {.is-warning}

GPUs compatible with Virtual Function I/O Mediated devices (vfio-mdev) can be split into multiple virtual GPUs (vGPUs).

In turned, these vGPUs can then be assigned to virtual machines or containers.

Contrary to paravirtualized GPUs (e.g. virtio-gpu), virtual GPUs do not need specialized drivers.

How to do so?

Preparation

Modify the system allocated to the GPU in the BIOS/UEFI

Some computers allow you to modify the system memory allocated or shared with the integrated GPU, which may allow you to create more vGPUs. {.is-info}

  • Before the host operating system boots up, you need to enter the BIOS/UEFI and to look for a setting called GPU aperture size, or GPU shared memory.

  • Use the highest possible value.

System memory will be reserved for the GPU, so make sure you have enough system memory to accomodate both the GPU and your operating system. {.is-info}

Create a virtual GPU

Upon reboot, you should then be able to list available GPUs using the mdevctl command.

  • List available virtual GPUs:
mdevctl types

0000:00:02.0
  i915-GVTg_V5_1
    Available instances: 1
    Device API: vfio-pci
    Description: low_gm_size: 512MB, high_gm_size: 2048MB, fence: 4, resolution: 1920x1200, weight: 16
  i915-GVTg_V5_2
    Available instances: 2
    Device API: vfio-pci
    Description: low_gm_size: 256MB, high_gm_size: 1024MB, fence: 4, resolution: 1920x1200, weight: 8
  i915-GVTg_V5_4
    Available instances: 5
    Device API: vfio-pci
    Description: low_gm_size: 128MB, high_gm_size: 512MB, fence: 4, resolution: 1920x1200, weight: 4
  i915-GVTg_V5_8
    Available instances: 7
    Device API: vfio-pci
    Description: low_gm_size: 64MB, high_gm_size: 384MB, fence: 4, resolution: 1024x768, weight: 2

Increasing the system memory allocated to the GPU (GPU aperture size), as shown in the previous section, may increase the number and kind of available instances. {.is-info}

In this case, the i915-GVTg_V5_4 kind seems to offer the best trade-offs between the available resolution and the number of available instances.

  • Generate a universally unique identifier (UUID) with the following command:
uuidgen

7686131b-b229-4768-a02c-35d1dbed7c66
  • Start a vGPU based on the kind i915-GVTg_V5_4 using the previously generated UUID
sudo mdevctl start -u 7686131b-b229-4768-a02c-35d1dbed7c66 -p 0000:00:02.0 --type i915-GVTg_V5_4
  • Define, or make this vGPU permanent.
sudo mdevctl define -u 7686131b-b229-4768-a02c-35d1dbed7c66
  • Set the vGPU to auto-start after the host boots up, so that it is available to guest virtual machines without further action
sudo mdevctl modify -u 7686131b-b229-4768-a02c-35d1dbed7c66 --auto
  • Finally, verify that the vGPU has successfully been created and is set to auto-start:
mdevctl list -d

7686131b-b229-4768-a02c-35d1dbed7c66 0000:00:02.0 i915-GVTg_V5_4 auto (active)

Great you have

Assign a virtual GPU to a virtual machine

  • Add that segment to a virtual machine's definition. Make sure the provided uuid matches the previously generated UUID.
<domain>
[...]
<device>
[...]
    <hostdev mode="subsystem" type="mdev" managed="no" model="vfio-pci" display="on" ramfb="on">
      <source>
        <address uuid="7686131b-b229-4768-a02c-35d1dbed7c66"/>
      </source>
      <address type="pci" domain="0x0000" bus="0x09" slot="0x00" function="0x0"/>
    </hostdev>
[...]
</device>
[...]
</domain>

Notice that the RAMFB is set to on, which activates Drect Memory Access Buffers (DMA-BUFs), making available the output of a virtual monitor before the guest operating system takes over {.is-info}

Configure Spice / SDL

To-do

Remove any video device

  • Remove any video device such as virtio-gpu and set the last one to the none.
<domain>
[...]
<device>
[...]
    <video>
    	<model type="none"/>
    </video>
[...]
</device>
[...]
</domain>
  • Then starts the domain

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