196 lines
7.2 KiB
ReStructuredText
196 lines
7.2 KiB
ReStructuredText
Virtio-GPU Venus
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================
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Venus is a Virtio-GPU protocol for Vulkan command serialization. The protocol
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definition and codegen are hosted at `venus-protocol
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<https://gitlab.freedesktop.org/olv/venus-protocol>`__. The renderer is
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hosted at `virglrenderer
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<https://gitlab.freedesktop.org/virgl/virglrenderer>`__.
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The protocol is still under development. This driver and the renderer are
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both considered experimental.
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Requirements
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------------
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The Venus renderer requires
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- Vulkan 1.1
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- ``VK_EXT_external_memory_dma_buf``
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- ``VK_EXT_image_drm_format_modifier``
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- ``VK_EXT_queue_family_foreign``
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from the host driver. However, it violates the spec in some places currently
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and also relies on implementation-defined behaviors in others. It is not
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expected to work on all drivers meeting the requirements. It has only been
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tested with
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- ANV 21.1 or later
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- RADV 21.1 or later (the host kernel must have
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``CONFIG_TRANSPARENT_HUGEPAGE`` disabled because of this `KVM issue
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<https://github.com/google/security-research/security/advisories/GHSA-7wq5-phmq-m584>`__)
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- TURNIP 22.0 or later
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- Mali r32p0 or later
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The Venus driver requires supports for
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- ``VIRTGPU_PARAM_RESOURCE_BLOB``
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- ``VIRTGPU_PARAM_HOST_VISIBLE``
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- ``VIRTGPU_PARAM_CROSS_DEVICE``
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- ``VIRTGPU_PARAM_CONTEXT_INIT``
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from the virtio-gpu kernel driver, unless vtest is used. That usually means
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the guest kernel should be at least 5.16 or have the parameters back ported,
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paired with hypervisors such as `crosvm
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<https://chromium.googlesource.com/chromiumos/platform/crosvm>`__, or `patched
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qemu
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<https://www.collabora.com/news-and-blog/blog/2021/11/26/venus-on-qemu-enabling-new-virtual-vulkan-driver/>`__.
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vtest
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-----
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The simplest way to test Venus is to use virglrenderer's vtest server. To
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build virglrenderer with Venus support and to start the vtest server,
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.. code-block:: console
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$ git clone https://gitlab.freedesktop.org/virgl/virglrenderer.git
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$ cd virglrenderer
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$ meson out -Dvenus-experimental=true
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$ ninja -C out
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$ ./out/vtest/virgl_test_server --venus
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In another shell,
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.. code-block:: console
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$ export VK_ICD_FILENAMES=<path-to-virtio_icd.x86_64.json>
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$ export VN_DEBUG=vtest
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$ vulkaninfo
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$ vkcube
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If the host driver of the system is not new enough, it is a good idea to build
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the host driver as well when building the Venus driver. Just remember to set
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:envvar:`VK_ICD_FILENAMES` when starting the vtest server so that the vtest
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server finds the locally built host driver.
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Virtio-GPU
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----------
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The driver requires ``VIRTGPU_PARAM_CONTEXT_INIT`` from the virtio-gpu kernel
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driver, which was upstreamed in kernel 5.16.
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crosvm is written in Rust. To build crosvm, make sure Rust has been installed
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and
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.. code-block:: console
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$ git clone --recurse-submodules \
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https://chromium.googlesource.com/chromiumos/platform/crosvm
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$ cd crosvm
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$ RUSTFLAGS="-L<path-to-virglrenderer>/out/src" cargo build \
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--features "x wl-dmabuf virgl_renderer virgl_renderer_next default-no-sandbox"
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Note that crosvm must be built with ``default-no-sandbox`` or started with
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``--disable-sandbox`` in this setup.
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This is how one might want to start crosvm
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.. code-block:: console
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$ sudo LD_LIBRARY_PATH=<...> VK_ICD_FILENAMES=<...> ./target/debug/crosvm run \
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--gpu vulkan=true \
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--display-window-keyboard \
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--display-window-mouse \
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--host_ip 192.168.0.1 \
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--netmask 255.255.255.0 \
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--mac 12:34:56:78:9a:bc \
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--rwdisk disk.img \
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-p root=/dev/vda1 \
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<path-to-bzImage>
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assuming a working system is installed to partition 1 of ``disk.img``.
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``sudo`` or ``CAP_NET_ADMIN`` is needed to set up the TAP network device.
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Virtio-GPU and Virtio-WL
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------------------------
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In this setup, the guest userspace uses Xwayland and a special Wayland
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compositor to connect guest X11/Wayland clients to the host Wayland
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compositor, using Virtio-WL as the transport. This setup is more tedious, but
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that should hopefully change over time.
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For now, the guest kernel must be built from the ``chromeos-5.10`` branch of
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the `Chrome OS kernel
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<https://chromium.googlesource.com/chromiumos/third_party/kernel>`__.
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To build minigbm and to enable minigbm support in virglrenderer,
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.. code-block:: console
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$ git clone https://chromium.googlesource.com/chromiumos/platform/minigbm
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$ cd minigbm
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$ CFLAGS=-DDRV_<I915-or-your-driver> OUT=out DESTDIR=out/install make install
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$ cd ../virglrenderer
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$ meson configure out -Dminigbm_allocation=true
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$ ninja -C out
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Make sure a host Wayland compositor is running. Replace
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``--display-window-keyboard --display-window-mouse`` by
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``--wayland-sock=<path-to-wayland-socket>`` when starting crosvm.
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In the guest, build and start sommelier, the special Wayland compositor,
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.. code-block:: console
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$ git clone https://chromium.googlesource.com/chromiumos/platform2
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$ cd platform2/vm_tools/sommelier
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$ meson out -Dxwayland_path=/usr/bin/Xwayland -Dxwayland_gl_driver_path=/usr/lib/dri
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$ ninja -C out
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$ sudo chmod 777 /dev/wl0
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$ ./out/sommelier -X --glamor
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--xwayland-gl-driver-path=<path-to-locally-built-gl-driver> \
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sleep infinity
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Optional Requirements
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---------------------
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When virglrenderer is built with ``-Dminigbm_allocation=true``, the Venus
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renderer might need to import GBM BOs. The imports will fail unless the host
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driver supports the formats, especially multi-planar ones, and the DRM format
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modifiers of the GBM BOs.
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In the future, if virglrenderer's ``virgl_renderer_export_fence`` is
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supported, the Venus renderer will require ``VK_KHR_external_fence_fd`` with
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``VK_EXTERNAL_FENCE_HANDLE_TYPE_SYNC_FD_BIT`` from the host driver.
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VK_MEMORY_PROPERTY_HOST_VISIBLE_BIT
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-----------------------------------
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The Venus renderer makes assumptions about ``VkDeviceMemory`` that has
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``VK_MEMORY_PROPERTY_HOST_VISIBLE_BIT``. The assumptions are illegal and rely
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on the current behaviors of the host drivers. It should be possible to remove
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some of the assumptions and incrementally improve compatibilities with more
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host drivers by imposing platform-specific requirements. But the long-term
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plan is to create a new Vulkan extension for the host drivers to address this
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specific use case.
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The Venus renderer assumes a device memory that has
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``VK_MEMORY_PROPERTY_HOST_VISIBLE_BIT`` can be exported as a mmapable dma-buf
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(in the future, the plan is to export the device memory as an opaque fd). It
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chains ``VkExportMemoryAllocateInfo`` to ``VkMemoryAllocateInfo`` without
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checking if the host driver can export the device memory.
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The dma-buf is mapped (in the future, the plan is to import the opaque fd and
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call ``vkMapMemory``) but the mapping is not accessed. Instead, the mapping
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is passed to ``KVM_SET_USER_MEMORY_REGION``. The hypervisor, host KVM, and
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the guest kernel work together to set up a write-back or write-combined guest
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mapping (see ``virtio_gpu_vram_mmap`` of the virtio-gpu kernel driver). CPU
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accesses to the device memory are via the guest mapping, and are assumed to be
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coherent when the device memory also has
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``VK_MEMORY_PROPERTY_HOST_COHERENT_BIT``.
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While the Venus renderer can force a ``VkDeviceMemory`` external, it does not
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force a ``VkImage`` or a ``VkBuffer`` external. As a result, it can bind an
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external device memory to a non-external resource.
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