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Merged Drivers

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From Open-IOV
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The following page will provide specifications and details on the current state of host DRM + VFIO-Mdev drivers in support of various vendors. +

In the context of this page the term "Merged Driver" refers to drivers which allow simultaneous acceleration of the host using a device's PF (Physical Function) and acceleration of guests using one or more VFs (Virtual Functions) created using the same device. +

+Merged functionality is currently supported for drivers which both make use of VFIO-Mdev and SR-IOV functionality depending on the vendor and driver implementation.

An absence of critical technical documentation has historically slowed growth and adoption of developer ecosystems for GPU virtualization. +

This CC-BY-4.0 licensed content can either be used with attribution, or used as inspiration for new documentation, created by GPU vendors for public commercial distribution as developer documentation. +

+Where possible, this documentation will clearly label dates and versions of observed-but-not-guaranteed behaviour vs. vendor-documented stable interfaces/behaviour with guarantees of forward or backward compatibility.

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Intel i915

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Intel's slides mention the ability to accelerate up to '8 VMs plus DOM0'. Source: https://01.org/sites/default/files/documentation/an_introduction_to_intel_gvt-g_for_external.pdf
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Intel currently supports host DRM and VFIO-Mdev/SR-IOV functionality in it's current i915 driver sources (VFIO-Mdev/GVT-g) and upstreaming i915 driver sources (VFIO-Mdev/SR-IOV). +

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Known Issues

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  1. SR-IOV functionality is undocumented in the i915 driver API documentation.
    Confirmed affected versions: *
    A diagram depicting i915's shared host + VFIO-Mdev driver model.
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Resolved Issues

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  1. Multiplexing functionality requires use modified KVM and Xen hypervisors (KVMGT/XenGT).
    Confirmed affected versions:     current i915 driver sources (GVT-g)
    Fixed in:     upstreaming i915 driver sources (SR-IOV)
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Nvidia

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Known Issues

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  1. Power management on laptops running mediated graphics functionality may causes graphical errors when not plugged in to AC power.
    Confirmed affected versions: 460.32.01, 460.73.04
    Possible mitigation: lore.kernel.org: "vfio/pci: Change the PF power state to D0 before enabling VFs"
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  2. VFIO-vmalloc errors may occur as a result of page collisions between host & guest on GPUs with smaller VRAM frame buffer sizes.
    Confirmed affected versions: 460.32.01, 460.73.04
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  3. Mdev service daemons may crash or load incorrectly requiring a service restart or reboot during host runtime.
    Confirmed affected versions: 460.32.01, 460.73.04, 510.xx.xx
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  4. Guest drivers fail to initialize correctly when VFIO-Mdev devices are mixed with some VFIO passthrough'd USB hubs.
    Confirmed affected versions: 460.73.01
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Resolved Issues

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  1. Upon executing QEMU mdev device initialization for a second Mdev an IOMMU group binding error occurs in QEMU preventing the device from being brought up.
    Confirmed affected versions: 460.32.01, 460.73.04
    Fixed in: 510.xx.xx
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Module Configuration

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Depending on your use-case the use of some additional parameters when booting the system may be helpful. +

Here is a list of some parameters which may be used when loading the module via GRUB or Systemd-boot. +

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Module Parameters +
Parameter +Description +Side-Effects +
cudahost=1 +Allows use of CUDA on the host system. +Windows guests may fail. +
nvidia.vgpukvm=0 +Disables GPU virtualization on the host. + +
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AMDGPU

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At this time AMDGPU does not currently support VFIO-Mdev functionality. It may be possible to incorporate Mdev Mode mediated device support similar to those functions in nvidia.ko and i915.ko in the Linux kernel's AMDGPU driver sources to produce a driver suitable for merged host+guest DRM for use with AMD GPU devices. +

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Known Issues

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  1. Host DRM does not work alongside guest VFIO-Mdev.
    Confirmed affected versions: *
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  2. The amdgpu kernel module doesn't contain hooks for guest signalling via irqfd & ioeventfd used for VFIO-mdev callbacks.
    Confirmed affected versions: *
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