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peppergrayxyz/qemu-vulkan-virtio.md

Created December 11, 2024 18:11

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QEMU with VirtIO GPU Vulkan Support
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qemu-vulkan-virtio.md

QEMU with VirtIO GPU Vulkan Support

 

With its latest reales qemu added the Venus patches so that
virtio-gpu now support venus encapsulation for vulkan. This is one
more piece to the puzzle towards full Vulkan support.

An outdated blog post on clollabora described in 2021 how to enable
3D acceleration of Vulkan applications in QEMU through the Venus
experimental Vulkan driver for VirtIO-GPU with a local development
environment. Following up on the outdated write up, this is how its
done today.

Definitions

 

Let's start with the brief description of the projects mentioned in
the post & extend them:

  * QEMU is a machine emulator
  * VirGL is an OpenGL driver for VirtIO-GPU, available in Mesa.
  * Venus is an experimental Vulkan driver for VirtIO-GPU, also
    available in Mesa.
  * Virglrenderer is a library that enables hardware acceleration to
    VM guests, effectively translating commands from the two drivers
    just mentioned to either OpenGL or Vulkan.
  * libvirt is an API for managing platform virtualization
  * virt-manager is a desktop user interface for managing virtual
    machines through libvirt

Merged Patches:

  * 2024-08-14 venus: make cross-device optional merged in mesa 24.2
  * 2024-11-25 KVM: Stop grabbing references to PFNMAP'd pages merged
    in linux 6.13
  * 2024-11-12 Support blob memory and venus on qemu merged in qemu
    9.2.0

Work in progress:

  * libvirt Add support for more virtio-vga-gl arguments #638
  * virt-manager Add support for Venus / Vulkan VirtIO-GPU driver #
    362

Prerequisites

 

Make sure you have the proper version installed on the host:

  * linux kernel >= 6.13 built with CONFIG_UDMABUF
  * working Vulkan and kvm setup
  * qemu >= 9.2.0

You can verify this like so:

$ uname -r
6.13.0
$ ls /dev/udmabuf
/dev/udmabuf
$ ls /dev/kvm
/dev/kvm
$ qemu-system-x86_64 --version
QEMU emulator version 9.2.0
Copyright (c) 2003-2024 Fabrice Bellard and the QEMU Project developers

For Vulkan to work you need the proper drivers to be installed for
your graphics card. To verfiy your setup, install vulkan-tools:

$ vulkaninfo --summary
==========
VULKANINFO
==========

Vulkan Instance Version: ...
...
$ vkcube
Selected GPU x: ..., type: ...

Building qemu

 

If your distro doesn't (yet) ship and updated version of qemu, you
can build it yourself from source:

wget https://download.qemu.org/qemu-9.2.0.tar.xz
tar xvJf qemu-9.2.0.tar.xz
cd qemu-9.2.0
mkdir build && cd build
../configure --target-list=x86_64-softmmu  \
  --enable-kvm                 \
  --enable-opengl              \
  --enable-virglrenderer       \
  --enable-gtk                 \
  --enable-sdl
make -j4

The configuration step will throgh errors if packages are missing.
Check the qemu wiki for further info what to install: https://
wiki.qemu.org/Hosts/Linux

Create and run an image for QEMU

 

Create an image & fetch the distro of your choice:

Host

 

ISO=ubuntu-24.10-desktop-amd64.iso
wget https://releases.ubuntu.com/oracular/ubuntu-24.10-desktop-amd64.iso

IMG=ubuntu-24-10.qcow2
qemu-img create -f qcow2 $IMG 16G

Run a live version or install the distro

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

Adjust the parameters accordingly:

  * smp: number of cpu cores
  * m: RAM
  * hostmem,size: VRAM

Guest

 

Install mesa-utilites and vulkan-tools to test the setup:

$ glxinfo -B

$ vkcube
Selected GPU x: ..., type: ...

If the deive is llvmpipe somehting is wrong. The device should be
virgl (...).

Troubleshooting

 

  * (host) add -d guest_errors to show error messages from the guest
  * (guest) try installing vulkan virtio drivers and mesa
  * check the original blog post

virt-manager

 

-- work in progress --

Currently this is work in progress, so there is no option to add
vulkan support in virt-manager. There are no fields to configure
this. Also xml doesnt work, because libvirt doesn't know about these
options either, so xml validation fails. There is however an option
for QEMU command-line passthrough which bypasses the validation.

If you setup a default machine with 4G of memory, you can do this:

  <qemu:commandline>
    <qemu:arg value="-device"/>
    <qemu:arg value="virtio-vga-gl,hostmem=4G,blob=true,venus=true"/>
    <qemu:arg value="-object"/>
    <qemu:arg value="memory-backend-memfd,id=mem1,size=4G"/>
    <qemu:arg value="-machine"/>
    <qemu:arg value="memory-backend=mem1"/>
    <qemu:arg value="-vga"/>
    <qemu:arg value="none"/>
  </qemu:commandline>

Which gives this error:

qemu-system-x86_64: virgl could not be initialized: -1

Changing the number from 4G to 4194304k (same as memory) leds to this
error:

qemu-system-x86_64: Spice: ../spice-0.15.2/server/red-qxl.cpp:435:spice_qxl_gl_scanout: condition `qxl_state->gl_draw_cookie == GL_DRAW_COOKIE_INVALID' failed

to be further investigated.

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