Subject: Re: [PATCH v6 4/5] arm64: kexec: Add support for crashkernel CMA reservation

From: Baoquan He <[email-masked]>
Date: Thu, 26 Feb 2026 17:33:36 +0800

On 02/24/26 at 04:53pm, Jinjie Ruan wrote:
> Commit 35c18f2933c5 ("Add a new optional ",cma" suffix to the
> crashkernel= command line option") and commit ab475510e042 ("kdump:
> implement reserve_crashkernel_cma") added CMA support for kdump
> crashkernel reservation.
> 
> Crash kernel memory reservation wastes production resources if too
> large, risks kdump failure if too small, and faces allocation difficulties
> on fragmented systems due to contiguous block constraints. The new
> CMA-based crashkernel reservation scheme splits the "large fixed
> reservation" into a "small fixed region + large CMA dynamic region": the
> CMA memory is available to userspace during normal operation to avoid
> waste, and is reclaimed for kdump upon crash—saving memory while
> improving reliability.
> 
> So extend crashkernel CMA reservation support to arm64. The following
> changes are made to enable CMA reservation:
> 
> - Parse and obtain the CMA reservation size along with other crashkernel
>   parameters.
> - Call reserve_crashkernel_cma() to allocate the CMA region for kdump.
> - Include the CMA-reserved ranges for kdump kernel to use.
> - Exclude the CMA-reserved ranges from the crash kernel memory to
>   prevent them from being exported through /proc/vmcore, which is already
>   done in the crash core.
> 
> Update kernel-parameters.txt to document CMA support for crashkernel on
> arm64 architecture.
> 
> Acked-by: Ard Biesheuvel <[email-masked]>
> Signed-off-by: Jinjie Ruan <[email-masked]>
> ---
> v3:
> - Add Acked-by.
> v2:
> - Free cmem in prepare_elf_headers()
> - Add the mtivation.
> ---
>  Documentation/admin-guide/kernel-parameters.txt | 2 +-
>  arch/arm64/kernel/machine_kexec_file.c          | 8 +++++++-
>  arch/arm64/mm/init.c                            | 5 +++--
>  3 files changed, 11 insertions(+), 4 deletions(-)
> 
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index cb850e5290c2..497f63b76898 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -1121,7 +1121,7 @@ Kernel parameters
>  			It will be ignored when crashkernel=X,high is not used
>  			or memory reserved is below 4G.
>  	crashkernel=size[KMG],cma
> -			[KNL, X86, ppc] Reserve additional crash kernel memory from
> +			[KNL, X86, ARM64, ppc] Reserve additional crash kernel memory from
                                          ~~~~ 
This should be written as 'PPC', even though it's not introduced in this patch.
===
 PPC     PowerPC architecture is enabled.
===

Other than this nit, the overral looks good to me.

>  			CMA. This reservation is usable by the first system's
>  			userspace memory and kernel movable allocations (memory
>  			balloon, zswap). Pages allocated from this memory range
......snip...