[Bug 1759920] Re: intel-microcode 3.20180312.0 causes lockup at login screen

[bmaupin]

Since this bug was marked as fixed I'm not sure what the best way to
proceed is. I went ahead and filed a new bug:
https://bugs.launchpad.net/ubuntu/+source/intel-microcode/+bug/1769335

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https://bugs.launchpad.net/bugs/1759920

Title:
  intel-microcode 3.20180312.0 causes lockup at login screen

Status in intel-microcode package in Ubuntu:
  Invalid
Status in linux package in Ubuntu:
  Invalid
Status in intel-microcode source package in Trusty:
  Invalid
Status in linux source package in Trusty:
  Fix Released
Status in intel-microcode source package in Xenial:
  Invalid
Status in linux source package in Xenial:
  Fix Released
Status in intel-microcode source package in Artful:
  Invalid
Status in linux source package in Artful:
  Fix Released

Bug description:
  [Impact]

   * Some systems experience kernel lockups after updating to the latest intel-microcode
     package or when receiving updated microcode from a BIOS update.

   * In many cases, the lockups occur before users can reach the login screen which makes
     it very difficult to debug/workaround.

  [Test Case]

   * The most reliable test case currently known is to install the sssd package. Lockups
     may occur during package installation (disable IBPB by writing 0 to
     /proc/sys/kernel/ibpb_enabled to prevent this from happening). A lockup will most
     likely occur just after booting the system up as the lock screen is displayed.

  [Regression Potential]

   * The fix is in the task switching code of the kernel so complexity of the change is
     relatively high.

  [Original Report]

  I don't know if this is a problem with the kernel or the microcode,
  but we have a significant number of computers in our organization (on
  both 16.04 and 17.10) that fail if they have both updated.  Booting
  with either linux-image-4.13.0-36-generic or intel-microcode
  3.20180108.0+really20170707ubuntu17.10.1 allows all these computers to
  boot.

  ## Workaround ##
  1. Boot the system with the dis_ucode_ldr kernel boot parameter to temporary avoid the problem:
     https://wiki.ubuntu.com/Kernel/KernelBootParameters
  2. Install the previous version of package from
     https://launchpad.net/~ubuntu-security-proposed/+archive/ubuntu/ppa/+build/14261530/+files/intel-microcode_3.20180108.0+really20170707ubuntu16.04.1_amd64.deb
  3. (Optional) Hold the package so that it won't be upgraded accidentally
     sudo apt-mark hold intel-microcode

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