Virtio-GPU Venus

Venus is a Virtio-GPU protocol for Vulkan command serialization. The protocol definition and codegen are hosted at venus-protocol. The renderer is hosted at virglrenderer.

Requirements

The Venus renderer requires

from the host driver. However, it violates the spec and relies on implementation-defined behaviors to support vkMapMemory (see below). It is not expected to work on all drivers meeting the requirements. It has only been tested with:

  • ANV 21.1 or later

    • Note: with Intel Meteor Lake or xe driver, you need 6.16+ kernel and 11.0+ QEMU with -accel kvm,honor-guest-pat=on (request to default that on is here).

  • RADV 21.1 or later
  • NVIDIA (Proprietary) 570.86 or later

    • Note: if paired with Intel CPU, you need 6.16+ kernel and 11.0+ QEMU with -accel kvm,honor-guest-pat=on (request to default that on is here).

  • ARM Mali (Proprietary) r32p0 or later

  • Turnip 22.0 or later

  • PanVK 25.1 or later

  • Lavapipe 22.1 or later

The Venus driver requires supports for

  • VIRTGPU_PARAM_3D_FEATURES

  • VIRTGPU_PARAM_CAPSET_QUERY_FIX

  • VIRTGPU_PARAM_RESOURCE_BLOB

  • VIRTGPU_PARAM_HOST_VISIBLE

  • VIRTGPU_PARAM_CONTEXT_INIT

from the virtio-gpu kernel driver, unless vtest is used. That usually means the guest kernel should be at least 5.16 or have the parameters back ported, paired with hypervisors such as crosvm, or QEMU.

vtest

The simplest way to test Venus is to use virglrenderer’s vtest server. To build virglrenderer with Venus support and to start the vtest server,

$ git clone https://gitlab.freedesktop.org/virgl/virglrenderer.git
$ cd virglrenderer
$ meson out -Dvenus=true
$ meson compile -C out
$ meson devenv -C out
$ ./vtest/virgl_test_server --venus
$ exit

In another shell,

$ export VK_DRIVER_FILES=<path-to-virtio_icd.x86_64.json>
$ export VN_DEBUG=vtest
$ vulkaninfo
$ vkcube

If the host driver of the system is not new enough, it is a good idea to build the host driver as well when building the Venus driver. Just remember to set VK_DRIVER_FILES when starting the vtest server so that the vtest server finds the locally built host driver.

QEMU

This is how one might want to start QEMU

$ ./qemu-system-x86_64                                             \
      -enable-kvm                                                  \
      -M q35                                                       \
      -smp 8                                                       \
      -m 4G                                                        \
      -cpu host                                                    \
      -net nic,model=virtio                                        \
      -net user,hostfwd=tcp::2222-:22                              \
      -device virtio-gpu-gl,hostmem=4G,blob=true,venus=true        \
      -vga none                                                    \
      -display sdl,gl=on,show-cursor=on                            \
      -usb -device usb-tablet                                      \
      -object memory-backend-memfd,id=mem1,size=4G                 \
      -machine memory-backend=mem1                                 \
      -hda $IMG

To build QEMU, this is how one might want to configure it

$ cd <QEMU source dir>
$ mkdir build && cd build
$ ../configure                                                     \
      --prefix=$HOME/.local                                        \
      --target-list=x86_64-softmmu                                 \
      --enable-kvm                                                 \
      --disable-werror                                             \
      --enable-opengl                                              \
      --enable-virglrenderer                                       \
      --enable-gtk                                                 \
      --enable-sdl
$ make -j$(nproc)

crosvm

crosvm is written in Rust. To build crosvm, make sure Rust has been installed and

$ git clone --recurse-submodules \
      https://chromium.googlesource.com/chromiumos/platform/crosvm
$ cd crosvm
$ RUSTFLAGS="-L<path-to-virglrenderer>/out/src" cargo build \
      --features "x wl-dmabuf virgl_renderer virgl_renderer_next default-no-sandbox"

Note that crosvm must be built with default-no-sandbox or started with --disable-sandbox in this setup.

This is how one might want to start crosvm

$ sudo LD_LIBRARY_PATH=<...> VK_DRIVER_FILES=<...> ./target/debug/crosvm run \
      --gpu vulkan=true \
      --gpu-render-server path=<path-to-virglrenderer>/out/server/virgl_render_server \
      --display-window-keyboard \
      --display-window-mouse \
      --net "host-ip 192.168.0.1,netmask=255.255.255.0,mac=12:34:56:78:9a:bc" \
      --rwdisk disk.img \
      -p root=/dev/vda1 \
      <path-to-bzImage>

assuming a working system is installed to partition 1 of disk.img. sudo or CAP_NET_ADMIN is needed to set up the TAP network device.

Android Cuttlefish

Venus isn’t supported in the upstream Cuttlefish yet, for venus_guest_angle mode used in Mesa CI against Android 16 AOSP, the instruction is here.

Optional Requirements

In the future, if virglrenderer’s virgl_renderer_export_fence is supported, the Venus renderer will require VK_KHR_external_fence_fd with VK_EXTERNAL_FENCE_HANDLE_TYPE_SYNC_FD_BIT from the host driver.

VK_MEMORY_PROPERTY_HOST_VISIBLE_BIT

The Venus renderer makes assumptions about VkDeviceMemory that has VK_MEMORY_PROPERTY_HOST_VISIBLE_BIT. The assumptions are illegal and rely on the current behaviors of the host drivers. It should be possible to remove some of the assumptions and incrementally improve compatibilities with more host drivers by imposing platform-specific requirements. But the long-term plan is to create a new Vulkan extension for the host drivers to address this specific use case.

The Venus renderer assumes a device memory that has VK_MEMORY_PROPERTY_HOST_VISIBLE_BIT can be exported as a mmapable dma-buf (in the future, the plan is to export the device memory as an opaque fd). It chains VkExportMemoryAllocateInfo to VkMemoryAllocateInfo without checking if the host driver can export the device memory.

The dma-buf is mapped (in the future, the plan is to import the opaque fd and call vkMapMemory) but the mapping is not accessed. Instead, the mapping is passed to KVM_SET_USER_MEMORY_REGION. The hypervisor, host KVM, and the guest kernel work together to set up a write-back or write-combined guest mapping (see virtio_gpu_vram_mmap of the virtio-gpu kernel driver). CPU accesses to the device memory are via the guest mapping, and are assumed to be coherent when the device memory also has VK_MEMORY_PROPERTY_HOST_COHERENT_BIT.

While the Venus renderer can force a VkDeviceMemory external, it does not force a VkImage or a VkBuffer external. As a result, it can bind an external device memory to a non-external resource.