Re: [PATCH v3] arm64/kdump: pass dm-crypt keys to kdump kernel

[Will Deacon <will@kernel.org>]

On Fri, Jan 23, 2026 at 04:13:25PM +0800, Coiby Xu wrote:
> CONFIG_CRASH_DM_CRYPT has been introduced to support LUKS-encrypted
> device dump target by addressing two challenges [1],
>  - Kdump kernel may not be able to decrypt the LUKS partition. For some
>    machines, a system administrator may not have a chance to enter the
>    password to decrypt the device in kdump initramfs after the 1st kernel
>    crashes
> 
>  - LUKS2 by default use the memory-hard Argon2 key derivation function
>    which is quite memory-consuming compared to the limited memory reserved
>    for kdump.
> 
> To also enable this feature for ARM64, we only need to add device tree
> property dmcryptkeys [2] as similar to elfcorehdr to pass the memory
> address of the stored info of dm-crypt keys to the kdump kernel. Since
> this property is only needed by the kdump kenrel, it won't be exposed to
> user space.
> 
> [1] https://lore.kernel.org/all/20250502011246.99238-1-coxu@redhat.com/
> [2] https://github.com/devicetree-org/dt-schema/pull/181
> 
> Cc: Arnaud Lefebvre <arnaud.lefebvre@clever-cloud.com>
> Cc: Baoquan he <bhe@redhat.com>
> Cc: Dave Young <dyoung@redhat.com>
> Cc: Kairui Song <ryncsn@gmail.com>
> Cc: Pingfan Liu <kernelfans@gmail.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Krzysztof Kozlowski <krzk@kernel.org>
> Cc: Rob Herring <robh@kernel.org>
> Signed-off-by: Coiby Xu <coxu@redhat.com>
> ---
> v3
> - Delete the property after reading it [Rob Herring]
> 
> v2
> - Krzysztof
>   - Use imperative mood for commit message
>   - Add dt-schema ABI Documentation 
>     https://github.com/devicetree-org/dt-schema/pull/181
> - Don't print dm-crypt keys address via pr_debug
> 
> 
>  arch/arm64/kernel/machine_kexec_file.c |  9 +++++++++
>  drivers/of/fdt.c                       | 21 +++++++++++++++++++++
>  drivers/of/kexec.c                     | 19 +++++++++++++++++++
>  3 files changed, 49 insertions(+)
> 
> diff --git a/arch/arm64/kernel/machine_kexec_file.c b/arch/arm64/kernel/machine_kexec_file.c
> index 410060ebd86d..5f3bad8ca96d 100644
> --- a/arch/arm64/kernel/machine_kexec_file.c
> +++ b/arch/arm64/kernel/machine_kexec_file.c
> @@ -134,6 +134,15 @@ int load_other_segments(struct kimage *image,
>  
>  		kexec_dprintk("Loaded elf core header at 0x%lx bufsz=0x%lx memsz=0x%lx\n",
>  			      image->elf_load_addr, kbuf.bufsz, kbuf.memsz);
> +
> +		ret = crash_load_dm_crypt_keys(image);
> +
> +		if (ret == -ENOENT) {
> +			kexec_dprintk("No dm crypt key to load\n");
> +		} else if (ret) {
> +			pr_err("Failed to load dm crypt keys\n");
> +			goto out_err;
> +		}

This looks like an unusual mixture of kexec_dprintk() and pr_err().

Stepping back a second, why do we need to print anything from the arch
code at all? It looks like crash_load_dm_crypt_keys() already prints for
the -ENOENT case so I'd be inclined just to do:

	ret = crash_load_dm_crypt_keys(image);
	if (ret)
		goto out_err;

Will