[Bug 1831789] Re: Add "dis_ucode_ldr" to linux boot options for Recovery Mode

[Launchpad Bug Tracker]

Status changed to 'Confirmed' because the bug affects multiple users.

** Changed in: grub2 (Ubuntu Focal)
       Status: New => Confirmed

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https://bugs.launchpad.net/bugs/1831789

Title:
  Add "dis_ucode_ldr" to linux boot options for Recovery Mode

Status in grub2 package in Ubuntu:
  Triaged
Status in grub2 source package in Focal:
  Confirmed
Status in grub2 source package in Groovy:
  Triaged

Bug description:
  Due to some recent problems with a microcode update which broke
  booting of some laptops I suggest adding "dis_ucode_ldr" to recovery
  mode boot options to allow booting after a bad microcode update.

  See the following topics that describe the problems:
   - https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1829620
   - https://github.com/intel/Intel-Linux-Processor-Microcode-Data-Files/issues/1

  When such problems occur it's very hard to see that the microcode
  loading is the issue, the booting just hangs at the purple screen,
  even removing "quiet splash" or using the recovery option will not
  show the error.

  We'll need to double check that dis_ucode_ldr works as expected across all architectures.
  According to the kernel docs (Documentation/admin-guide/kernel-parameters.txt), dis_ucode_ldr is x86 only, so my guess is that it will be ignored for other architectures. According to the kernel code  (arch/x86/kernel/cpu/microcode/core.c), dis_ucode_ldr works for both AMD and Intel.
  I have some time tomorrow on test this on a ARM device.

  This was also discussed Ubuntu Developer mailing list where it was
  suggested to post this here, see: https://lists.ubuntu.com/archives
  /ubuntu-devel/2019-June/040725.html

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