Exactly. I did the "verification-done-bionic" step for 18.2.2 in comment
#12 above; and unfortunately I don't have an affected school nearby,
where I could test 18.2.8 in cosmic, and installing cosmic in a remote
school would be hard.

Thanks a lot Timo!

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  Black screen on skylake after 18.0 => 18.2 update

Status in Mesa:
  Fix Released
Status in linux package in Ubuntu:
  Fix Released
Status in mesa package in Ubuntu:
  Fix Released
Status in linux source package in Bionic:
Status in mesa source package in Bionic:
  Fix Committed
Status in linux source package in Cosmic:
Status in mesa source package in Cosmic:
  Fix Committed

Bug description:
  Several schools reported black screens after normally updating their Ubuntu 
boxes from 18.0.5-0ubuntu0~18.04.1 to 18.2.2-0ubuntu1~18.04.1.

  Downgrading mesa fixes the problem.

  lspci: 00:02.0 VGA compatible controller [0300]: Intel Corporation HD
  Graphics 530 [8086:1912] (rev 06)         Subsystem: ASUSTeK Computer
  Inc. HD Graphics 530 [1043:8694]    Kernel modules: i915

  Unfortunately I can't find a lot of useful information, here are some bits:
   * systemctl --failed says "gpu-manager" and "lightdm" have failed
   * Xorg.log is clean: https://termbin.com/6l2b
   * dmesg too: https://termbin.com/ip4e
   * It happens on lightdm/MATE, I don't know about Ubuntu GNOME.
   * If one runs `xinit` from ssh, it fails with:
  i965: Failed to submit batchbuffer: Invalid argument

  This is caused by mesa assuming that soft-pinning on GEN8+ is working
  since kernel 4.5, but in fact this issue wasn't fixed until 4.19.3. So
  a proper fix would be to backport commits from 4.19.3/4.20 to fix GTT
  sizes/pin flags, but that's left for future.

  [Test case]
  install fixed mesa or kernel, check that the regression is fixed

  [Regression potential]
  mesa: shouldn't be any, it just reverts the change to always soft-pin
  (TODO kernel: adds commits from upstream stable, which have been well tested 
upstream by now)

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