Intel GVT-g
Intel GVT-g is a technology that provides mediated device passthrough for Intel GPUs (Broadwell and newer). It can be used to virtualize the GPU for multiple guest VMs, effectively providing near-native graphics performance in the VM and still letting your host use the virtualized GPU normally. This is useful if you want accelerated graphics in Windows VMs running on ultrabooks without dedicated GPUs for full device passthrough. (Similar technologies exist for NVIDIA and AMD GPUs, but they're available only in the "professional" GPU lines like Quadro, Radeon Pro and so on.)
There is also a variant of this technology called GVT-d - it is essentially Intel's name for full device passthrough with the vfio-pci driver. With GVT-d, the host cannot use the virtualized GPU.
Configuration
You'll have to create a virtual GPU (vGPU) first, then assign it to your VM. The guest with a vGPU sees it as a "regular" GPU - just install the latest native drivers. (The vGPU actually does need specialized drivers to work correctly, but all the required changes are present in the latest upstream Linux/Windows drivers.)
You'll need to:
- Use at least Linux 4.16 and QEMU 2.12.
- Add
i915.enable_gvt=1to your kernel parameters to enable GPU virtualization. - Find the PCI address and domain number of your GPU (
$GVT_PCIand$GVT_DOMin commands below), as it resides in/sys/bus/pci/devices. It looks like this:0000:00:02.0- you can look it up by runninglspci -D -nn, looking forVGA compatible controller: Intel Corporation HD Graphics ...and noting down the address on the left. - Generate the vGPU GUID (
$GVT_GUIDin commands below) which you'll use to create and assign the vGPU. A single virtual GPU can be assigned only to a single VM - create as many GUIDs as you want vGPUs. (You can do so by runninguuidgen.)
After rebooting with the i915.enable_gvt=1 flag, you should be able to create vGPUs - there are multiple vGPU types you can create, which mainly differ in the amount of resources dedicated to that vGPU. You can look up what types are available in your system (and cat description inside of each type to discover what it's capable of) like this:
# ls /sys/devices/pci${GVT_DOM}/$GVT_PCI/mdev_supported_types
i915-GVTg_V5_1 # Video memory: <512MB, 2048MB>, resolution: up to 1920x1200
i915-GVTg_V5_2 # Video memory: <256MB, 1024MB>, resolution: up to 1920x1200
i915-GVTg_V5_4 # Video memory: <128MB, 512MB>, resolution: up to 1920x1200
i915-GVTg_V5_8 # Video memory: <64MB, 384MB>, resolution: up to 1024x768
Pick a type you want to use - we'll refer to it as $GVT_TYPE below. Use the GUID you've created to create a vGPU with a chosen type:
# echo "$GVT_GUID" > "/sys/devices/pci${GVT_DOM}/$GVT_PCI/mdev_supported_types/$GVT_TYPE/create"
You can repeat this as many times as you want with different GUIDs. All created vGPUs will land in /sys/bus/pci/devices/$GVT_PCI/ - if you'd like to remove a vGPU, you can do:
# echo 1 > /sys/bus/pci/devices/$GVT_PCI/$GVT_GUID/remove
Finally, to create a VM with the virtualized GPU, add this parameter to the QEMU command line:
-device vfio-pci,sysfsdev=/sys/bus/pci/devices/$GVT_PCI/$GVT_GUID,rombar=0
Troubleshooting
Missing mdev_supported_types directory
If you have followed instructions and added i915.enable_gvt=1 kernel parameter, but there is still no /sys/bus/pci/devices/0000:02:00.0/mdev_supported_types directory, probably your hardware is not supported. Check dmesg log for this message:
$ dmesg | grep -i gvt
[ 4.227468] [drm] Unsupported device. GVT-g is disabled
If that is the case, you may want to check upstream for support plans. For example, for the "Coffee Lake" (CFL) platform support, see https://github.com/intel/gvt-linux/issues/53