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

[Sourabh Jain]

On 06/08/26 11:03, Coiby Xu wrote:
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...@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?

This API is used to verify crash hotplug support, which is not directly 
related to crash_dm_crypt_keys.
It also seems to be generally useful.

- Sourabh Jain



- Sourabh Jain
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