[PATCH v5 0/8] Support virtio-gpu DRM native context

[Dmitry Osipenko <dmitry.osipenko@collabora.com>]

This patchset adds DRM native context support to VirtIO-GPU on Qemu.

Contarary to Virgl and Venus contexts that mediates high level GFX APIs,
DRM native context [1] mediates lower level kernel driver UAPI, which
reflects in a less CPU overhead and less/simpler code needed to support it.
DRM context consists of a host and guest parts that have to be implemented
for each GPU driver. On a guest side, DRM context presents a virtual GPU as
a real/native host GPU device for GL/VK applications.

[1] https://www.youtube.com/watch?v=9sFP_yddLLQ

Today there are four known DRM native context drivers existing in a wild:

  - Freedreno (Qualcomm SoC GPUs), completely upstreamed
  - AMDGPU, mostly merged into upstreams
  - Intel (i915), merge requests are opened
  - Asahi (Apple SoC GPUs), WIP status


# How to try out DRM context:

1. DRM context uses host blobs and requires latest developer version 
of Linux kernel [2] that has necessary KVM fixes.

[2] https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/

2. Use latest libvirglrenderer from upstream git/main for Freedreno
and AMDGPU native contexts. For Intel use patches [3].

[3] https://gitlab.freedesktop.org/virgl/virglrenderer/-/merge_requests/1384

3. On guest, use latest Mesa version for Freedreno. For AMDGPU use
Mesa patches [4], for Intel [5].

[4] https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/21658
[5] https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/29870

4. On guest, use latest Linux kernel v6.6+. Apply patch [6] if you're
   running Xorg in guest.

[6] https://lore.kernel.org/dri-devel/20241020224725.179937-1-dmitry.osipenko@collabora.com/

Example Qemu cmdline that enables DRM context:

  qemu-system-x86_64 -device virtio-vga-gl,hostmem=4G,blob=on,drm_native_context=on \
      -machine q35,accel=kvm,memory-backend=mem1 \
      -object memory-backend-memfd,id=mem1,size=8G -m 8G


# Note about known performance problem in Qemu:

DRM contexts are mapping host blobs extensively and these mapping
operations work slowly in Qemu. Exact reason is unknown. Mappings work
fast on Crosvm For DRM contexts this problem is more visible than for
Venus/Virgl.

Changelog:

v5: - Added r-bs from Akihiko Odaki.

    - Added acks from Michael Tsirkin.

    - Fixed compilation warning using older version of virglrenderer that
      was reported by Alex Bennée. Noticed that I need to keep old
      virgl_write_fence() code around for the older virglrenderer in
      "Support  asynchronous fencing" patch, so added it back and verified
      that old virglrenderer works properly.

    - Added new patch from Alex Bennée that adds more virtio-gpu 
      documentation with a couple corrections and additions to it from me.

    - Rebased patches on top of latest staging tree.

v4: - Improved SDL2/dmabuf patch by reusing existing Meson X11 config 
      option, better handling EGL error and extending comment telling
      that it's safe to enable SDL2 EGL preference hint. As was suggested
      by Akihiko Odaki.

    - Replaced another QSLIST_FOREACH_SAFE with QSLIST_EMPTY+FIRST in
      the async-fencing patch for more consistency of the code. As was
      suggested by Akihiko Odaki.

    - Added missing braces around if-statement that was spotted by
      Alex Bennée.

    - Renamed 'drm=on' option of virtio-gpu-gl device to 
      'drm_native_context=on' for more clarity as was suggested by 
      Alex Bennée. Haven't added added new context-type option that 
      was also proposed by Alex, might do it with a separate patch.
      This context-type option will duplicate and depecate existing
      options, but in a longer run likely will be worthwhile adding
      it.

    - Dropped Linux headers-update patch as headers has been updated
      in the staging tree.

v3: - Improved EGL presence-check code on X11 systems for the SDL2
      hint that prefers EGL over GLX by using better ifdefs and checking
      Xlib presence at a build time to avoid build failure if lib SDL2
      and system are configured with a disabled X11 support. Also added
      clarifying comment telling that X11 hint doesn't affect Wayland
      systems. Suggested by Akihiko Odaki.

    - Corrected strerror(err) that used negative error where it should
      be positive and vice versa that was caught by Akihiko Odaki. Added
      clarifying comment for the case where we get positive error code
      from virglrenderer that differs from other virglrenderer API functions.

    - Improved QSLIST usage by dropping mutex protecting the async fence
      list and using atomic variant of QSLIST helpers instead. Switched away
      from using FOREACH helper to improve readability of the code, showing
      that we don't precess list in unoptimal way. Like was suggested by
      Akihiko Odaki.

    - Updated patchset base to Venus v18.

v2: - Updated SDL2-dmabuf patch by making use of error_report() and
      checking presense of X11+EGL in the system before making SDL2
      to prefer EGL backend over GLX, suggested by Akihiko Odaki.

    - Improved SDL2's dmabuf-presence check that wasn't done properly
      in v1, where EGL was set up only after first console was fully
      inited, and thus, SDL's display .has_dmabuf callback didn't work
      for the first console. Now dmabuf support status is pre-checked
      before console is registered.

    - Updated commit description of the patch that fixes SDL2's context
      switching logic with a more detailed explanation of the problem.
      Suggested by Akihiko Odaki.

    - Corrected rebase typo in the async-fencing patch and switched
      async-fencing to use a sigle-linked list instead of the double,
      as was suggested by Akihiko Odaki.

    - Replaced "=true" with "=on" in the DRM native context documentation
      example and made virtio_gpu_virgl_init() to fail with a error message
      if DRM context can't be initialized instead of giving a warning
      message, as was suggested by Akihiko Odaki.

    - Added patchew's dependecy tag to the cover letter as was suggested by
      Akihiko Odaki.


Alex Bennée (1):
  docs/system: Expand the virtio-gpu documentation

Dmitry Osipenko (6):
  ui/sdl2: Restore original context after new context creation
  virtio-gpu: Handle virgl fence creation errors
  virtio-gpu: Support asynchronous fencing
  virtio-gpu: Support DRM native context
  ui/sdl2: Don't disable scanout when display is refreshed
  ui/gtk: Don't disable scanout when display is refreshed

Pierre-Eric Pelloux-Prayer (1):
  ui/sdl2: Implement dpy dmabuf functions

 docs/system/devices/virtio-gpu.rst | 105 +++++++++++++++++--
 hw/display/virtio-gpu-gl.c         |   5 +
 hw/display/virtio-gpu-virgl.c      | 159 ++++++++++++++++++++++++++++-
 hw/display/virtio-gpu.c            |  15 +++
 include/hw/virtio/virtio-gpu.h     |  16 +++
 include/ui/sdl2.h                  |   7 ++
 meson.build                        |   6 +-
 ui/gtk-egl.c                       |   1 -
 ui/gtk-gl-area.c                   |   1 -
 ui/sdl2-gl.c                       |  68 +++++++++++-
 ui/sdl2.c                          |  42 ++++++++
 11 files changed, 411 insertions(+), 14 deletions(-)

-- 
2.47.1