@cpaelzer and @mfo thank both of your reviewing and sponsoring.

@cpaelzer yes, if anything break, it's on me. Here's the PPA with the builds:
https://launchpad.net/~canonical-support-eng/+archive/ubuntu/sf361158

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https://bugs.launchpad.net/bugs/2024479

Title:
  kdump fails on arm64 when offset is not specified

Status in kexec-tools package in Ubuntu:
  Fix Committed
Status in linux package in Ubuntu:
  Incomplete
Status in kexec-tools source package in Focal:
  In Progress
Status in linux source package in Focal:
  Won't Fix
Status in kexec-tools source package in Jammy:
  In Progress
Status in linux source package in Jammy:
  Incomplete
Status in kexec-tools source package in Kinetic:
  Won't Fix
Status in linux source package in Kinetic:
  Won't Fix
Status in kexec-tools source package in Lunar:
  In Progress
Status in kexec-tools source package in Mantic:
  Fix Committed

Bug description:
  [Description]

  kdump fails on arm64, on machines with a lot of memory when offeset is not 
specified,
  e.g when /etc/default/grub.d/kdump-tools.cfg looks like:
  GRUB_CMDLINE_LINUX_DEFAULT="$GRUB_CMDLINE_LINUX_DEFAULT crashkernel=4G"

  If kdump-tools.cfg specifies the offset e.g.:
  GRUB_CMDLINE_LINUX_DEFAULT="$GRUB_CMDLINE_LINUX_DEFAULT crashkernel=4G@4G"
  it works ok.

  The reason for this is that the kernel needs to allocate memory for the 
crashkernel both
  in low and high memory.
  This is addressed in kernel 6.2.
  In addition kexec-tools needs to support more than one crash kernel regions.

  [Fix]

  To address this issue the following upstrem commits are needed:

  - From the kernel side:

      commit a9ae89df737756d92f0e14873339cf393f7f7eb0
      Author: Zhen Lei <thunder.leiz...@huawei.com>
      Date: Wed Nov 16 20:10:44 2022 +0800

      arm64: kdump: Support crashkernel=X fall back to reserve region
  above DMA zones

      commit a149cf00b158e1793a8dd89ca492379c366300d2
      Author: Zhen Lei <thunder.leiz...@huawei.com>
      Date: Wed Nov 16 20:10:43 2022 +0800

      arm64: kdump: Provide default size when crashkernel=Y,low is not
  specified

  - From kexec-tools:

      commit b5a34a20984c4ad27cc5054d9957af8130b42a50
      Author: Chen Zhou <chenzho...@huawei.com>
      Date: Mon Jan 10 18:20:08 2022 +0800

      arm64: support more than one crash kernel regions

  Affected releases:
  Jammy, Focal, Bionic

  For Bionic we won't fix it as we need to backport a lot of code and the 
regression potential is too high.
  The same applies for the Focal 5.4 kernel.
  Only the 5.15 hwe focal kernel will be fixed.

  [Test]

  You need a machine (can be a VM too) with large memory e.g. 128G.
  Install linux-crashdump and trigger a crash.
  It won't work unless the offset is specified because the memory crashkernel 
cannot be allocated.

  With the patches applied it works as expected without having to
  specify the offset.

  [Regression Potential]

  KERNEL 5.15:
  To address this problem in the 5.15 kernel we need to pull in 7 commits (see 
[Other] section for details.
  All the commits are changing code only for arm64 architecture and only the 
code related to reserving the crashkernel.
  This means that any regression potential will affect only the arm64 
architecture and in particular the crash/kdump functionality.
  However, since the reservation of the crashkernel occurs at boot up, 
potentially things could go wrong there as well.

  KEXEX - FOCAL:
  To fix the kexec_tools in focal we need to pull in 6 commits (see [Other 
section for details]). They all cherry pick.
  Four out of six commits touch only arm64 code. Any regression potential 
because of these commits  would regard either crashdump or kexec functionality.
  Commit cf977b1af9ec67fab adds code without altering current functionality.
  Commit f4ce0706d9574aecb7 adds functionality to read elf notes. In practive 
it moves the code from vmcore-dmesg.c  to elf_info.c so it can be used by other 
features.

  KEXEC - JAMMY, LUNAR, MANTIC:
  Commit b5a34a20984c is pulled in, it cherry-picks. It changes only arm64 
code. It enables kexec to recognise that teh reserved kernel may use more than 
one kernel region. Things could go worng when gatherinng a crashdump.

  [Other]

  Commits to backport

  - MANTIC:

      kernel 6.3: not affected

      kexec-tools:
      b5a34a20984c4ad27cc5054d9957af8130b42a50 arm64: support more than one 
crash kernel regions

  - LUNAR:

      kernel 6.2: not affected

      kexec-tools:
      b5a34a20984c4ad27cc5054d9957af8130b42a50 arm64: support more than one 
crash kernel regions

  - KINETIC: WON'T FIX

      Kinetic won't be fixed as it EOLs soon.

  - JAMMY:

      kernel (5.15 kernel):

      a9ae89df737756d92f0e14873339cf393f7f7eb0 arm64: kdump: Support 
crashkernel=X fall back to reserve region above DMA zones
      a149cf00b158e1793a8dd89ca492379c366300d2 arm64: kdump: Provide default 
size when crashkernel=Y,low is not specified
      4890cc18f94979b406f95708f8cb238eb2d0e5a9 arm64/mm: Define 
defer_reserve_crashkernel()
      8f0f104e2ab6eed4cad3b111dc206f843bda43ea arm64: kdump: Do not allocate 
crash low memory if not needed
      5832f1ae50600ac6b2b6d00cfef42d33a9473f06 docs: kdump: Update the 
crashkernel description for arm64
      944a45abfabc171fd121315ff0d5e62b11cb5d6f arm64: kdump: Reimplement 
crashkernel=X
      d339f1584f0acf32b32326627fa3b48e6e65c599 arm64: mm: use 
IS_ENABLED(CONFIG_KEXEC_CORE) instead of #ifdef

      kexec-tools:

      b5a34a20984c4ad27cc5054d9957af8130b42a50 arm64: support more than
  one crash kernel regions

  - FOCAL:

      Kernel 5.4: Won't fix because of high regression potential.
      Instead the 5.15-hwe kernel can be used.

      kexec-tools:

      b5a34a20984c4ad27cc5054d9957af8130b42a50 arm64: support more than one 
crash kernel regions
      2572b8d702e452624bdb8d7b7c39f458e7dcf2ce arm64: kdump: deal with a lot of 
resource entries in /proc/iomem
      cf977b1af9ec67fabcc6a625589c49c52d07b11d kexec: add variant helper 
functions for handling memory regions
      f736104f533290b4ce6fbfbca74abde9ffd3888c arm64: kexec: allocate memory 
space avoiding reserved regions
      64c49f27d88024eaab990d2cd6069289cf853098 arm64: Add support to read 
PHYS_OFFSET from 'kcore' - pt_note or pt_load (if available)
      f4ce0706d9574aecb7d4aa9af7208a1bc9b6afb4 util_lib: Add functionality to 
read elf notes

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