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

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Message-ID: <aXs0UnFE1fEa8Yxu@Rk>
Date: Thu, 29 Jan 2026 18:40:23 +0800
From: Coiby Xu <coxu@...hat.com>
To: Will Deacon <will@...nel.org>
Cc: kexec@...ts.infradead.org, linux-arm-kernel@...ts.infradead.org, 
	Arnaud Lefebvre <arnaud.lefebvre@...ver-cloud.com>, Baoquan he <bhe@...hat.com>, Dave Young <dyoung@...hat.com>, 
	Kairui Song <ryncsn@...il.com>, Pingfan Liu <kernelfans@...il.com>, 
	Andrew Morton <akpm@...ux-foundation.org>, Krzysztof Kozlowski <krzk@...nel.org>, 
	Rob Herring <robh@...nel.org>, Catalin Marinas <catalin.marinas@....com>, 
	Saravana Kannan <saravanak@...nel.org>, open list <linux-kernel@...r.kernel.org>, 
	"open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE" <devicetree@...r.kernel.org>
Subject: Re: [PATCH v3] arm64/kdump: pass dm-crypt keys to kdump kernel

On Mon, Jan 26, 2026 at 02:36:08PM +0000, Will Deacon wrote:
>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@...ver-cloud.com>
>> Cc: Baoquan he <bhe@...hat.com>
>> Cc: Dave Young <dyoung@...hat.com>
>> Cc: Kairui Song <ryncsn@...il.com>
>> Cc: Pingfan Liu <kernelfans@...il.com>
>> Cc: Andrew Morton <akpm@...ux-foundation.org>
>> Cc: Krzysztof Kozlowski <krzk@...nel.org>
>> Cc: Rob Herring <robh@...nel.org>
>> Signed-off-by: Coiby Xu <coxu@...hat.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
>

Hi Will,

Thanks for carefully reviewing the patch! Yeah, crash_load_dm_crypt_keys
already prints for the -ENOTENT case, good catch! And it's also a good
idea to not let the arch code print anything since
crash_load_dm_crypt_keys is a better place. I'll make
crash_load_dm_crypt_keys print more logs and also return 0 for the case
of -ENOENT. This can make the arch code more succinct.


-- 
Best regards,
Coiby