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Virtual Function I/O Mediated devices (vfio-mdev) Create and Configure Virtual Function I/O Mediated devices (vfio-mdev) true 2022-07-27T23:53:40.933Z markdown 2022-07-21T21:10:41.046Z

Configure Virtual Function I/O Mediated devices

Virtual Function I/O Mediated devices (vfio-mdev) allows you to split a compatible GPU into multiple virtual GPUs (vGPUs). These vGPUs can then be assigned to a virtual machine, just as real GPUs.

These instructions only cover Intel GPUs that are compatible with vfio-mdev (5th to 10th generation). Since generation 11th, Intel graphics do not support vfio-mdev but SR-IOV. {.is-info}

Preparation

Update the GRUB

  • On a freshly deployed edition of Phyllome OS optimized for Intel Graphics such as Phyllome OS Desktop II, make sure that the GRUB has been updated.
sudo grub2-mkconfig -o /boot/grub2/grub.cfg
  • Then reboot your computer
sudo reboot

Modify GPU Memory in BIOS/UEFI

Only available for Intel Graphics cards {.is-info}

Some computers allow you to modify the GPU memory allocated your desktop-based computers. It will reserve system memory for the GPUs.

To do so, you need to enter the BIOS/UEFI and to look for a setting called GPU Aperture size, or GPU memory.

Use the highest value possible, but make sure you have enough system memory to accomodate both the GPU and your operating system.

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
  • You may need to increase GPU aperture size if there is no available instance.

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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