[Bug 1759920] Re: intel-microcode 3.20180312.0 causes lockup at login screen(w/ linux-image-4.13.0-37-generic)

[Michael Mulqueen]

Is a lack of testing for trusty going to prevent a patch for
xenial/artful? We don't have any machines on trusty to test it with, but
if it's going to block the whole patch then we might be able to wipe an
affected machine and install trusty to test it.

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Title:
  intel-microcode 3.20180312.0 causes lockup at login screen(w/ linux-
  image-4.13.0-37-generic)

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 Committed
Status in intel-microcode source package in Xenial:
  Invalid
Status in linux source package in Xenial:
  Fix Committed
Status in intel-microcode source package in Artful:
  Invalid
Status in linux source package in Artful:
  Fix Committed

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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