[Bug 2127792] Re: Images are corrupted on blackwell GPUs

[Mitchell Augustin]

Regarding the only remaining autopkgtest failure
(https://autopkgtest.ubuntu.com/packages/g/gnome-remote-
desktop/plucky/s390x)

I believe this is a false positive caused by a testbed issue:

ERROR: Clock skew detected. File
/tmp/autopkgtest.smWt6S/build.8yX/src/obj-s390x-linux-gnu/../meson.build
has a time stamp 43.0856s in the future

I can see very frequent examples of this from runs of this test on the prior Plucky version on s390x as well:
https://autopkgtest.ubuntu.com/results/autopkgtest-plucky/plucky/s390x/g/gnome-remote-desktop/20250902_211805_45458@/log.gz

(and on many other failures on that same page).

I propose a migration-reference/0 run to unblock this

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https://bugs.launchpad.net/bugs/2127792

Title:
  Images are corrupted on blackwell GPUs

Status in gnome-remote-desktop package in Ubuntu:
  Fix Released
Status in gnome-remote-desktop source package in Noble:
  Fix Committed
Status in gnome-remote-desktop source package in Plucky:
  Fix Committed
Status in gnome-remote-desktop source package in Questing:
  Fix Committed
Status in gnome-remote-desktop source package in Resolute:
  Fix Released

Bug description:
  There is image distorsion in gnome-remote-desktop when a Blackwell GPU
  is in use and NVENC is responsible for the video streaming.

  Upstream issue: https://gitlab.gnome.org/GNOME/gnome-remote-
  desktop/-/issues/263

  A fix was just released by nvidia upstream, and also backported to GNOME 48: https://gitlab.gnome.org/GNOME/gnome-remote-desktop/-/merge_requests/344
  https://gitlab.gnome.org/GNOME/gnome-remote-desktop/-/merge_requests/346

  ---------------------------
  SRU Justification:

  [ Impact ]

   * This is a hardware enablement SRU.

   * gnome-remote-desktop, when used alongside NVENC for video
  streaming, simply does not work, because the image is broken.

   * With the above, the streaming is fixed.

  [ Fix ]

   * Nvidia devices never supported `NV_ENC_PARAMS_FRAME_FIELD_MODE_MBAFF`.
  Though the code worked for past, it causes interlaced line artifacts on
  Blackwell GPUs.

  * Using `NV_ENC_PARAMS_FRAME_FIELD_MODE_FRAME` and changing
  `grd-cuda-avc-utils` to produce progressive frames works on
  Blackwell and on older GPU generations.

  [ Test Plan ]

  1. Use a DUT that has a Blackwell GPU
  (https://en.wikipedia.org/wiki/Blackwell_(microarchitecture)#Blackwell_dies)

  2. Enable Remote Login from the Gnome Settings on the DUT with a
  monitor plugged in.

  3. Install Reminna from Snap (via the edge channel) on your client.
  This version supports NVENC, the .deb does not.

  4. On the server with a Blackwell GPU, test gnome-remote-desktop with
  and without the fix using software rendering, or with the monitor
  unplugged (which should have the same impact)

  5. On the server with a Blackwell GPU, run `sudo chmod 666
  /dev/dri/renderD128` to enable GPU acceleration with RDP.

  4. Run the same test, now with GPU acceleration enabled. Make sure
  which backend is in use. This can be checked by running `nvidia-smi
  dmon` and observing an encoder activity >0%. The repro only occurs
  when the NVENC path is used. CPU encoding path or non-H264 streaming
  is unaffected

  6. Run the same tests (with and without software rendering) on an
  older GPU generation (Maxwell, ideally)

  [ Where problems could occur ]

   * Given the nature of the fix, it should not impact non-nvidia machines.
   * Also, the  fix comes from nvidia themsleves, and it's in GNOME 48 and 49 already, so it's pretty safe.

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