ACK: [SRU][J][PATCH 0/7] kdump fails on arm64 when offset is not specified

[Roxana Nicolescu]

On 10/07/2023 14:56, Ioanna Alifieraki wrote:
> BugLink: https://bugs.launchpad.net/bugs/2024479
>
> [Impact]
>
> 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 at 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.
>
> To address this issue the following upstrem commits are needed:
>
>  From the kernel side :
> commit a9ae89df737756d92f0e14873339cf393f7f7eb0
> Author: Zhen Lei <thunder.leizhen at 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.leizhen at huawei.com>
> Date: Wed Nov 16 20:10:43 2022 +0800
>
> arm64: kdump: Provide default size when crashkernel=Y,low is not specified
>
> [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).
> The commits cherrypick or need minor context adjustments.
> 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/kexec functionality.
> However, since the reservation of the crashkernel occurs at boot up, potentially things could go wrong there as well.
>
> [Other]
>
> Commits to backport
> *** 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
>
> Anshuman Khandual (1):
>    arm64/mm: Define defer_reserve_crashkernel()
>
> Chen Zhou (1):
>    arm64: kdump: Reimplement crashkernel=X
>
> Jisheng Zhang (1):
>    arm64: mm: use IS_ENABLED(CONFIG_KEXEC_CORE) instead of #ifdef
>
> Zhen Lei (4):
>    docs: kdump: Update the crashkernel description for arm64
>    arm64: kdump: Do not allocate crash low memory if not needed
>    arm64: kdump: Provide default size when crashkernel=Y,low is not
>      specified
>    arm64: kdump: Support crashkernel=X fall back to reserve region above
>      DMA zones
>
>   .../admin-guide/kernel-parameters.txt         | 15 +--
>   arch/arm64/include/asm/memory.h               |  5 +
>   arch/arm64/kernel/machine_kexec.c             |  9 +-
>   arch/arm64/kernel/machine_kexec_file.c        | 12 ++-
>   arch/arm64/mm/init.c                          | 98 ++++++++++++++++---
>   arch/arm64/mm/mmu.c                           |  6 +-
>   6 files changed, 116 insertions(+), 29 deletions(-)
>
LGTM.

Acked-by: Roxana Nicolescu <roxana.nicolescu at canonical.com>