113 lines
4.3 KiB
ReStructuredText
113 lines
4.3 KiB
ReStructuredText
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SPDX-License-Identifier: GPL-2.0-or-later
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virtio-gpu
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==========
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This document explains the setup and usage of the virtio-gpu device.
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The virtio-gpu device paravirtualizes the GPU and display controller.
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Linux kernel support
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--------------------
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virtio-gpu requires a guest Linux kernel built with the
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``CONFIG_DRM_VIRTIO_GPU`` option.
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QEMU virtio-gpu variants
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------------------------
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QEMU virtio-gpu device variants come in the following form:
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* ``virtio-vga[-BACKEND]``
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* ``virtio-gpu[-BACKEND][-INTERFACE]``
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* ``vhost-user-vga``
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* ``vhost-user-pci``
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**Backends:** QEMU provides a 2D virtio-gpu backend, and two accelerated
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backends: virglrenderer ('gl' device label) and rutabaga_gfx ('rutabaga'
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device label). There is a vhost-user backend that runs the graphics stack
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in a separate process for improved isolation.
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**Interfaces:** QEMU further categorizes virtio-gpu device variants based
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on the interface exposed to the guest. The interfaces can be classified
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into VGA and non-VGA variants. The VGA ones are prefixed with virtio-vga
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or vhost-user-vga while the non-VGA ones are prefixed with virtio-gpu or
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vhost-user-gpu.
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The VGA ones always use the PCI interface, but for the non-VGA ones, the
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user can further pick between MMIO or PCI. For MMIO, the user can suffix
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the device name with -device, though vhost-user-gpu does not support MMIO.
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For PCI, the user can suffix it with -pci. Without these suffixes, the
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platform default will be chosen.
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virtio-gpu 2d
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-------------
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The default 2D backend only performs 2D operations. The guest needs to
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employ a software renderer for 3D graphics.
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Typically, the software renderer is provided by `Mesa`_ or `SwiftShader`_.
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Mesa's implementations (LLVMpipe, Lavapipe and virgl below) work out of box
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on typical modern Linux distributions.
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.. parsed-literal::
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-device virtio-gpu
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.. _Mesa: https://www.mesa3d.org/
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.. _SwiftShader: https://github.com/google/swiftshader
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virtio-gpu virglrenderer
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------------------------
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When using virgl accelerated graphics mode in the guest, OpenGL API calls
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are translated into an intermediate representation (see `Gallium3D`_). The
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intermediate representation is communicated to the host and the
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`virglrenderer`_ library on the host translates the intermediate
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representation back to OpenGL API calls.
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.. parsed-literal::
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-device virtio-gpu-gl
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.. _Gallium3D: https://www.freedesktop.org/wiki/Software/gallium/
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.. _virglrenderer: https://gitlab.freedesktop.org/virgl/virglrenderer/
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virtio-gpu rutabaga
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-------------------
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virtio-gpu can also leverage rutabaga_gfx to provide `gfxstream`_
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rendering and `Wayland display passthrough`_. With the gfxstream rendering
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mode, GLES and Vulkan calls are forwarded to the host with minimal
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modification.
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The crosvm book provides directions on how to build a `gfxstream-enabled
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rutabaga`_ and launch a `guest Wayland proxy`_.
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This device does require host blob support (``hostmem`` field below). The
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``hostmem`` field specifies the size of virtio-gpu host memory window.
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This is typically between 256M and 8G.
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At least one virtio-gpu capability set ("capset") must be specified when
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starting the device. The currently capsets supported are ``gfxstream-vulkan``
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and ``cross-domain`` for Linux guests. For Android guests, the experimental
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``x-gfxstream-gles`` and ``x-gfxstream-composer`` capsets are also supported.
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The device will try to auto-detect the wayland socket path if the
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``cross-domain`` capset name is set. The user may optionally specify
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``wayland-socket-path`` for non-standard paths.
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The ``wsi`` option can be set to ``surfaceless`` or ``headless``.
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Surfaceless doesn't create a native window surface, but does copy from the
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render target to the Pixman buffer if a virtio-gpu 2D hypercall is issued.
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Headless is like surfaceless, but doesn't copy to the Pixman buffer.
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Surfaceless is the default if ``wsi`` is not specified.
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.. parsed-literal::
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-device virtio-gpu-rutabaga,gfxstream-vulkan=on,cross-domain=on,
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hostmem=8G,wayland-socket-path=/tmp/nonstandard/mock_wayland.sock,
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wsi=headless
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.. _gfxstream: https://android.googlesource.com/platform/hardware/google/gfxstream/
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.. _Wayland display passthrough: https://www.youtube.com/watch?v=OZJiHMtIQ2M
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.. _gfxstream-enabled rutabaga: https://crosvm.dev/book/appendix/rutabaga_gfx.html
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.. _guest Wayland proxy: https://crosvm.dev/book/devices/wayland.html
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