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186 lines
5.6 KiB
Markdown
186 lines
5.6 KiB
Markdown
---
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title: Virtual Function I/O Mediated devices (vfio-mdev)
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description: Create and Configure Virtual Function I/O Mediated devices (vfio-mdev)
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published: true
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date: 2023-05-14T20:10:36.548Z
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tags:
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editor: markdown
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dateCreated: 2022-07-21T21:10:41.046Z
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---
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# Configure *vfio-mdev*
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> 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 Since generation 11th, *vfio-mdev* has been superseded by *SR-IOV*.
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{.is-warning}
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GPUs compatible with [Virtual Function I/O Mediated devices](https://www.kernel.org/doc/html/latest/driver-api/vfio-mediated-device.html) (vfio-mdev) can be split into multiple virtual GPUs (vGPUs).
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Then, these vGPUs can be assigned to virtual machines or containers.
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Contrary to paravirtualized GPUs (e.g. *virtio-gpu*), vGPUs can use the same driver as their parent GPU (e.g. a guest compatible with an Intel GPUs will be able to leverage an Intel-based vGPUs)
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## Modify the system allocated to the GPU in the BIOS/UEFI
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> Some computers allow you to modify the system memory allocated or shared with the integrated GPU, which may allow you to create more vGPUs.
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{.is-info}
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> For Intel integrated graphics cards only; rarely available on laptops computers.
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{.is-warning}
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* 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*.
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* Use the highest possible value.
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> 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.
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{.is-warning}
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## Preparation
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* Make sure the GRUB has been updated after [the first boot](https://wiki.phyllo.me/getstarted/disk#update-grub-and-reboot)
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## Procedure
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### Create a virtual GPU
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List available GPUs using the `mdevctl` software:
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```
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mdevctl types
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```
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```
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0000:00:02.0
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i915-GVTg_V5_1
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Available instances: 1
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Device API: vfio-pci
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Description: low_gm_size: 512MB, high_gm_size: 2048MB, fence: 4, resolution: 1920x1200, weight: 16
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i915-GVTg_V5_2
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Available instances: 2
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Device API: vfio-pci
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Description: low_gm_size: 256MB, high_gm_size: 1024MB, fence: 4, resolution: 1920x1200, weight: 8
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i915-GVTg_V5_4
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Available instances: 5
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Device API: vfio-pci
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Description: low_gm_size: 128MB, high_gm_size: 512MB, fence: 4, resolution: 1920x1200, weight: 4
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i915-GVTg_V5_8
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Available instances: 7
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Device API: vfio-pci
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Description: low_gm_size: 64MB, high_gm_size: 384MB, fence: 4, resolution: 1024x768, weight: 2
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```
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> Increasing the memory allocated to the GPU in the BIOS/EFI may increase the number and kind of available instances.
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{.is-info}
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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.
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* Generate a universally unique identifier (UUID) with the following command:
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```
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uuidgen
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```
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```
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7686131b-b229-4768-a02c-35d1dbed7c66
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```
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* Start a vGPU based on the kind `i915-GVTg_V5_4` using the previously generated UUID
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```
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sudo mdevctl start -u 7686131b-b229-4768-a02c-35d1dbed7c66 -p 0000:00:02.0 --type i915-GVTg_V5_4
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```
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* Define, or make this vGPU permanent:
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```
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sudo mdevctl define -u 7686131b-b229-4768-a02c-35d1dbed7c66
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```
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* Set the vGPU to auto-start after the host boots up:
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```
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sudo mdevctl modify -u 7686131b-b229-4768-a02c-35d1dbed7c66 --auto
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```
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* Finally, verify that the vGPU has successfully been created and is set to auto-start:
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```
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mdevctl list -d
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```
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```
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7686131b-b229-4768-a02c-35d1dbed7c66 0000:00:02.0 i915-GVTg_V5_4 auto (active)
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```
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### Assign a vGPU to a virtual machine
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* Add that segment to a virtual machine's definition. Make sure the provided `uuid` matches the previously generated UUID.
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```
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<domain type="kvm">
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[...]
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<device>
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[...]
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<hostdev mode="subsystem" type="mdev" managed="no" model="vfio-pci" display="on" ramfb="on">
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<source>
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<address uuid="7686131b-b229-4768-a02c-35d1dbed7c66"/>
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</source>
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<address type="pci" domain="0x0000" bus="0x09" slot="0x00" function="0x0"/>
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</hostdev>
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[...]
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</device>
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[...]
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</domain>
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```
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> Notice that the RAMFB is set to on, which activates Drect Memory Access Buffers (DMA-BUFs), making the output of a virtual monitor available before the guest operating system takes over.
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{.is-info}
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## Remove any video device or display devices
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* Remove any video device such as `virtio-gpu` and set the last one to the `none`.
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```
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<domain type="kvm">
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[...]
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<device>
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[...]
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<video>
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<model type="none"/>
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</video>
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[...]
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</device>
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[...]
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</domain>
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```
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* Then starts the domain
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## Configure Spice / SDL
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*To-do*
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## Troubleshooting
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### No or low number of available instances
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Increasing the memory allocated to the GPU (a.k.a. the GPU aperture size) may increase the number of available instances.
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Some computers allow you to modify the memory allocated or shared with the integrated GPU, which may allow you to create more vGPUs.
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* Before the host operating system boots up, enter the BIOS/UEFI and look for a setting called *GPU aperture size*, or *GPU shared memory*.
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* Use the highest possible value.
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> The memory will be reserved to the GPU, so make sure you have enough leftover memory to accomodate both the GPU and your operating system.
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{.is-info}
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## Resources
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* Official page for vfio-mdev: https://www.kernel.org/doc/html/latest/driver-api/vfio-mediated-device.html
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* Archlinux's *must-read entry* on Intel GVT-g: https://wiki.archlinux.org/title/Intel_GVT-g
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* DMA-BUF Linux documentation: https://www.kernel.org/doc/html/latest/driver-api/dma-buf.html
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---
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*[**Go to parent page**](https://wiki.phyllo.me/)* |