Comment 0 for bug 1831789

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