** Changed in: linux (Ubuntu Bionic)
       Status: In Progress => Fix Committed

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https://bugs.launchpad.net/bugs/1908219

Title:
  [drm:qxl_enc_commit [qxl]] *ERROR* head number too large or missing
  monitors config:

Status in linux package in Ubuntu:
  Fix Released
Status in linux source package in Bionic:
  Fix Committed

Bug description:
  [Impact]

  * Ubuntu 18.04 used as a guest in KVM with Spice/QXL in use may lead to a DRM 
error displayed during xorg launch:
  [drm:qxl_enc_commit [qxl]] *ERROR* head number too large or missing monitors 
config:         (ptrval), 0

  [Fix]

  * 00e5d217fa19bcbec13135898e1b9ca2c1c3e89b qxl: hook monitors_config
  updates into crtc, not encoder.

  [Test Case]

  * Ubuntu 18.04 desktop guest with 4.15-series kernel with Spice/QXL.
  * I used Ubuntu 20.04 as the host, but I was reported that the issue is 
similar also on Centos 7.8 used as a host.

  [Regression Potential]

  * Fix is limited to the QXL driver, so any regressions will be related
  to graphics (either potential drm errors or graphical artifacts).

  [Other]

  * This has been fixed in HWE kernels and in later Ubuntu releases. Only 
Bionic is affected.
  * According to the description in drivers/gpu/drm/qxl/qxl_dev.h:
  struct qxl_monitors_config {
        (...)
        uint16_t max_allowed; /* If it is 0 no fixed limit is given by the
                                 driver */
        (...)
  };

  In the message this value is 0 which should be a completely correct situation 
in that context. However, it is incorrectly compared against current qxl_output.
  This has been fixed soon after Bionic release and in Bionic is marked with:
  /* TODO: ugly, do better */

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