Re: [PATCH v8 4/5] arm64: kexec: Add support for crashkernel CMA reservation

From: "Rob Herring (Arm)" <robh@kernel.org>
To: Jinjie Ruan <ruanjinjie@huawei.com>
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Subject: Re: [PATCH v8 4/5] arm64: kexec: Add support for crashkernel CMA reservation
Date: Fri, 13 Mar 2026 16:56:59 -0500	[thread overview]
Message-ID: <177343901948.3415566.6726187926870600451.robh@kernel.org> (raw)
In-Reply-To: <20260302035315.3892241-5-ruanjinjie@huawei.com>


On Mon, 02 Mar 2026 11:53:14 +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: 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(-)
> 

Acked-by: Rob Herring (Arm) <robh@kernel.org>