[Bug 1954692] Re: Reconsider compressed kernels on arm64

[dann frazier]

@juliank my assumption is that nothing prevents it, other than someone
writing that code.

Attached is a patch for flash-kernel that will handle the compression,
if needed, of kernel images for the m400. One alternate solution might
be to try and copy the firmware-provided device tree data into a
different memory location before loading the kernel in the boot.scr
script. On one hand, that would limit the changes to code that only runs
on these devices. But on the other hand, the generated uImage/uInitrd
files wouldn't be usable for netbooting, as I don't think there's a way
to inject memory copy commands into a config file for u-boot's pxelinux
emulation.

Note that we'll need to update the MAAS image generation code as well to
keep that working.

** Patch added: "0001-Introduce-Boot-Kernel-Max-Size-and-support-for-compr.patch"
   https://bugs.launchpad.net/ubuntu/+source/flash-kernel/+bug/1954692/+attachment/5557834/+files/0001-Introduce-Boot-Kernel-Max-Size-and-support-for-compr.patch

** Also affects: maas-images
   Importance: Undecided
       Status: New

** Changed in: flash-kernel (Ubuntu)
       Status: New => In Progress

** Changed in: flash-kernel (Ubuntu)
     Assignee: (unassigned) => dann frazier (dannf)

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https://bugs.launchpad.net/bugs/1954692

Title:
  Reconsider compressed kernels on arm64

Status in maas-images:
  New
Status in flash-kernel package in Ubuntu:
  In Progress
Status in linux package in Ubuntu:
  Triaged

Bug description:
  Compressed kernel images were introduced in bug 1384955 to work around
  some limits on old u-boot systems. This in turn broke grub-check-
  signatures, meaning that while cloud images booted in secure boot, you
  could not upgrade grub or install new kernels on secure systems as
  that would trigger a "you have unsigned kernels" message. grub 2.06
  also fails to boot the images, as it verifies before decompressing.

  Work to fix grub to handle such images on arm64 for backward
  compatibility is tracked in bug 1954683. This bug is to reconsider
  whether the change is still necessary or could be removed in 22.04
  such that we can have proper UEFI executables again.

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