Re: [PATCH v3 09/10] crash_dump: Disallow configfs/crash_dm_crypt_key/reuse if crash hotplug supported

[Coiby Xu <coiby.xu@gmail.com>]

On Wed, Aug 05, 2026 at 05:39:28PM +0530, Sourabh Jain wrote:
>
>
>On 29/07/26 09:06, Coiby Xu wrote:
>>If crash hotplug is supported, dm-crypt keys saved to reserved memory
>>will be taken care of automatically. Thus it doesn't make sense to use
>>configfs/crash_dm_crypt_key/reuse. Reserving image->dm_crypt_keys_addr
>>is also unnecessary. Currently x86_64 and ppc64le have implemented
>>crash hotplug feature.
>>
>>Also update the doc accordingly. Note two doc issues are fixed as well.
>>
>>Fixes: 9ebfa8dcaea7 ("crash_dump: reuse saved dm crypt keys for CPU/memory hot-plugging")
>>Signed-off-by: Coiby Xu <coiby.xu@gmail.com>
>>---
>>  Documentation/admin-guide/kdump/kdump.rst | 16 ++++++++++------
>>  kernel/crash_dump_dm_crypt.c              | 23 ++++++++++++++++++++---
>>  2 files changed, 30 insertions(+), 9 deletions(-)
>>
>>diff --git a/Documentation/admin-guide/kdump/kdump.rst b/Documentation/admin-guide/kdump/kdump.rst
>>index 7587caadbae1..0bf2eb100a05 100644
>>--- a/Documentation/admin-guide/kdump/kdump.rst
>>+++ b/Documentation/admin-guide/kdump/kdump.rst
>>@@ -577,9 +577,10 @@ with /sys/kernel/config/crash_dm_crypt_keys for setup,
>>  1. Tell the first kernel what logon keys are needed to unlock the disk volumes,
>>      # Add key #1
>>-    mkdir /sys/kernel/config/crash_dm_crypt_keys/7d26b7b4-e342-4d2d-b660-7426b0996720
>>+    VOL1_UUID=7d26b7b4-e342-4d2d-b660-7426b0996720
>>+    mkdir /sys/kernel/config/crash_dm_crypt_keys/$VOL1_UUID
>>      # Add key #1's description
>>-    echo cryptsetup:7d26b7b4-e342-4d2d-b660-7426b0996720 > /sys/kernel/config/crash_dm_crypt_keys/description
>>+    echo cryptsetup:$VOL1_UUID > /sys/kernel/config/crash_dm_crypt_keys/$VOL1_UUID/description
>>      # how many keys do we have now?
>>      cat /sys/kernel/config/crash_dm_crypt_keys/count
>>@@ -591,15 +592,18 @@ with /sys/kernel/config/crash_dm_crypt_keys for setup,
>>      cat /sys/kernel/config/crash_dm_crypt_keys/count
>>      2
>>-    # To support CPU/memory hot-plugging, reuse keys already saved to reserved
>>-    # memory
>>-    echo true > /sys/kernel/config/crash_dm_crypt_key/reuse
>>-
>>  2. Load the dump-capture kernel
>>  3. After the dump-capture kerne get booted, restore the keys to user keyring
>>     echo yes > /sys/kernel/crash_dm_crypt_keys/restore
>>+For CPU/memory hot-plugging, you can reuse keys already saved to reserved
>>+memory before reloading the kdump image,
>>+    echo true > /sys/kernel/config/crash_dm_crypt_keys/reuse
>>+
>>+Note if crash hotplug is supported, this API is totally unnecessary thus will
>>+be disabled automatically.
>>+
>>  Contact
>>  =======
>>diff --git a/kernel/crash_dump_dm_crypt.c b/kernel/crash_dump_dm_crypt.c
>>index b5b78656cf06..46d6b31c3ca4 100644
>>--- a/kernel/crash_dump_dm_crypt.c
>>+++ b/kernel/crash_dump_dm_crypt.c
>>@@ -310,6 +310,15 @@ static ssize_t config_keys_reuse_show(struct config_item *item, char *page)
>>  	return sysfs_emit(page, "%d\n", is_dm_key_reused);
>>  }
>>+static bool crash_hotplug_support(struct kimage *image)
>>+{
>>+#ifdef CONFIG_CRASH_HOTPLUG
>>+	return image->hotplug_support;
>
>I don't think it is good idea to access kexec_crash_image properties without
>holding the kexec lock.

Thanks for raising the concern! Let's discuss this issue in [PATCH v3 03/10].

>
>Also, would it make sense to move this API somewhere else?

Can you help me understand why to move this API? Is it because using
ifdef in .c file is discouraged?

>
>- Sourabh Jain
[...]

-- 
Best regards,
Coiby