Re: [PATCH v9 4/5] arm64: kexec: Add support for crashkernel CMA reservation

[Breno Leitao <leitao@debian.org>]

On Mon, Mar 23, 2026 at 03:27:44PM +0800, 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: Rob Herring (Arm) <robh@kernel.org>
> Acked-by: Baoquan He <bhe@redhat.com>
> Acked-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
> Acked-by: Ard Biesheuvel <ardb@kernel.org>
> Signed-off-by: Jinjie Ruan <ruanjinjie@huawei.com>
> ---
> v7:
> - Correct the inclusion of CMA-reserved ranges for kdump
>   kernel in of/kexec.
> 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          | 2 +-
>  arch/arm64/mm/init.c                            | 5 +++--
>  drivers/of/fdt.c                                | 9 +++++----
>  drivers/of/kexec.c                              | 9 +++++++++
>  5 files changed, 19 insertions(+), 8 deletions(-)
> 
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index cb850e5290c2..afb3112510f7 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
>  			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
> diff --git a/arch/arm64/kernel/machine_kexec_file.c b/arch/arm64/kernel/machine_kexec_file.c
> index c338506a580b..cc577d77df00 100644
> --- a/arch/arm64/kernel/machine_kexec_file.c
> +++ b/arch/arm64/kernel/machine_kexec_file.c
> @@ -42,7 +42,7 @@ int arch_kimage_file_post_load_cleanup(struct kimage *image)
>  #ifdef CONFIG_CRASH_DUMP
>  unsigned int arch_get_system_nr_ranges(void)
>  {
> -	unsigned int nr_ranges = 2; /* for exclusion of crashkernel region */
> +	unsigned int nr_ranges = 2 + crashk_cma_cnt; /* for exclusion of crashkernel region */

You update arch_get_system_nr_ranges() to account for CMA ranges, but
prepare_elf_headers() in the same file (line 51) still has the
hardcoded:

        nr_ranges = 2; /* for exclusion of crashkernel region */

and does not exclude CMA ranges from cmem. If the generic crash core
handles CMA exclusion from vmcore, then shouldn't
arch_get_system_nr_ranges() also not need this change?