[PATCH v4 8/9] crash_dump: Disallow configfs/crash_dm_crypt_key/reuse if crash hotplug supported

[PATCH v4 8/9] crash_dump: Disallow configfs/crash_dm_crypt_key/reuse if crash hotplug supported

[Coiby Xu]

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. Not reserving
image->dm_crypt_keys_addr makes it implicitly to disallow using this
API. 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              | 13 +++++++++----
 2 files changed, 19 insertions(+), 10 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 b7629174e4db..3aaa0f9c3117 100644
--- a/kernel/crash_dump_dm_crypt.c
+++ b/kernel/crash_dump_dm_crypt.c
@@ -324,7 +324,7 @@ static ssize_t config_keys_reuse_store(struct config_item *item,
 
 	r = -EINVAL;
 	if (!kexec_crash_image || !kexec_crash_image->dm_crypt_keys_addr) {
-		pr_debug("dm-crypt keys haven't be saved to crash-reserved memory\n");
+		pr_debug("dm-crypt keys haven't be saved to crash-reserved memory or crash hotplug supported\n");
 		goto unlock;
 	}
 
@@ -519,9 +519,9 @@ int crash_load_dm_crypt_keys(struct kimage *image)
 void kexec_file_post_load_cleanup_dm_crypt(struct kimage *image)
 {
 	/*
-	 * For CPU/memory hot-plugging, the kdump image will be reloaded. Prevent
-	 * keys_header from being cleaned up during unloading when
-	 * is_dm_key_reused=true
+	 * For CPU/memory hot-plugging without CONFIG_CRASH_HOTPLUG, the whole kdump
+	 * image will be reloaded. Prevent keys_header from being cleaned up during
+	 * unloading when is_dm_key_reused=true
 	 */
 	if (!is_dm_key_reused) {
 		kfree_sensitive(keys_header);
@@ -532,6 +532,11 @@ void kexec_file_post_load_cleanup_dm_crypt(struct kimage *image)
 		mutex_unlock(&config_keys_subsys.su_mutex);
 		mutex_acquired = false;
 	}
+
+#ifdef CONFIG_CRASH_HOTPLUG
+	if (image->hotplug_support)
+		image->dm_crypt_keys_addr = 0;
+#endif
 }
 
 static int __init configfs_dmcrypt_keys_init(void)
-- 
2.55.0

[PATCH v4 9/9] Documentation: kdump: Add arm64 and ppc64le to encrypted dump target support list

[Coiby Xu]

The encrypted dump target support is now extended to arm64 and ppc64le.

Fixes: e3a84be1ec2f ("arm64,ppc64le/kdump: pass dm-crypt keys to kdump kernel")
Reported-by: Sourabh Jain <sourabhjain@linux.ibm.com>
Reviewed-by: Sourabh Jain <sourabhjain@linux.ibm.com>
Signed-off-by: Coiby Xu <coiby.xu@gmail.com>
---
 Documentation/admin-guide/kdump/kdump.rst | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/Documentation/admin-guide/kdump/kdump.rst b/Documentation/admin-guide/kdump/kdump.rst
index 0bf2eb100a05..36ad6125c670 100644
--- a/Documentation/admin-guide/kdump/kdump.rst
+++ b/Documentation/admin-guide/kdump/kdump.rst
@@ -572,8 +572,8 @@ Write the dump file to encrypted disk volume
 ============================================
 
 CONFIG_CRASH_DM_CRYPT can be enabled to support saving the dump file to an
-encrypted disk volume (only x86_64 supported for now). User space can interact
-with /sys/kernel/config/crash_dm_crypt_keys for setup,
+encrypted disk volume (only x86_64, arm64, ppc64le supported for now). User
+space can interact 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
-- 
2.55.0

Re: [PATCH v4 8/9] crash_dump: Disallow configfs/crash_dm_crypt_key/reuse if crash hotplug supported

[Sourabh Jain]

On 28/08/26 14:18, 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. Not reserving
> image->dm_crypt_keys_addr makes it implicitly to disallow using this
> API. 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              | 13 +++++++++----
>   2 files changed, 19 insertions(+), 10 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 b7629174e4db..3aaa0f9c3117 100644
> --- a/kernel/crash_dump_dm_crypt.c
> +++ b/kernel/crash_dump_dm_crypt.c
> @@ -324,7 +324,7 @@ static ssize_t config_keys_reuse_store(struct config_item *item,
>   
>   	r = -EINVAL;
>   	if (!kexec_crash_image || !kexec_crash_image->dm_crypt_keys_addr) {
> -		pr_debug("dm-crypt keys haven't be saved to crash-reserved memory\n");
> +		pr_debug("dm-crypt keys haven't be saved to crash-reserved memory or crash hotplug supported\n");

Nit: the above line is more than 100 characters. There is no
complaint from checkpatch, but I feel we should reduce it to
below 100 characters.

Also, I checked that we don't have pr_fmt defined for this file,
but we do have pr_debug and other pr_* calls. See if defining
pr_fmt helps reduce the character count in the above line.

But the overall idea of handling crash hotplug support with
crash dm-crypt looks good to me. So feel free to add:

Reviewed-by: Sourabh Jain sourabhjain@linux.ibm.com

Thanks,
Sourabh Jain


>   		goto unlock;
>   	}
>   
> @@ -519,9 +519,9 @@ int crash_load_dm_crypt_keys(struct kimage *image)
>   void kexec_file_post_load_cleanup_dm_crypt(struct kimage *image)
>   {
>   	/*
> -	 * For CPU/memory hot-plugging, the kdump image will be reloaded. Prevent
> -	 * keys_header from being cleaned up during unloading when
> -	 * is_dm_key_reused=true
> +	 * For CPU/memory hot-plugging without CONFIG_CRASH_HOTPLUG, the whole kdump
> +	 * image will be reloaded. Prevent keys_header from being cleaned up during
> +	 * unloading when is_dm_key_reused=true
>   	 */
>   	if (!is_dm_key_reused) {
>   		kfree_sensitive(keys_header);
> @@ -532,6 +532,11 @@ void kexec_file_post_load_cleanup_dm_crypt(struct kimage *image)
>   		mutex_unlock(&config_keys_subsys.su_mutex);
>   		mutex_acquired = false;
>   	}
> +
> +#ifdef CONFIG_CRASH_HOTPLUG
> +	if (image->hotplug_support)
> +		image->dm_crypt_keys_addr = 0;
> +#endif
>   }
>   
>   static int __init configfs_dmcrypt_keys_init(void)

Re: [PATCH v4 8/9] crash_dump: Disallow configfs/crash_dm_crypt_key/reuse if crash hotplug supported

[Coiby Xu]

On Sun, Aug 30, 2026 at 01:28:59PM +0530, Sourabh Jain wrote:
>
>
>On 28/08/26 14:18, 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. Not reserving
>>image->dm_crypt_keys_addr makes it implicitly to disallow using this
>>API. 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              | 13 +++++++++----
>>  2 files changed, 19 insertions(+), 10 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 b7629174e4db..3aaa0f9c3117 100644
>>--- a/kernel/crash_dump_dm_crypt.c
>>+++ b/kernel/crash_dump_dm_crypt.c
>>@@ -324,7 +324,7 @@ static ssize_t config_keys_reuse_store(struct config_item *item,
>>  	r = -EINVAL;
>>  	if (!kexec_crash_image || !kexec_crash_image->dm_crypt_keys_addr) {
>>-		pr_debug("dm-crypt keys haven't be saved to crash-reserved memory\n");
>>+		pr_debug("dm-crypt keys haven't be saved to crash-reserved memory or crash hotplug supported\n");
>
>Nit: the above line is more than 100 characters. There is no
>complaint from checkpatch, but I feel we should reduce it to
>below 100 characters.

Thanks for the reminder! Documentation/process/coding-style.rst
explicitly states,
     However, never break user-visible strings such as printk messages because
     that breaks the ability to grep for them.

In fact, scripts/checkpatch.pl will issue a SPLIT_STRING warning if we
break the user-visible strings. So I think this is accepted unless
kexec/kdump subsystem has a hard column limit.

>
>Also, I checked that we don't have pr_fmt defined for this file,
>but we do have pr_debug and other pr_* calls. See if defining
>pr_fmt helps reduce the character count in the above line.

If I'm not mistaken, pr_fmt only adds a prefix. So I don't think it will
help reduce the character count in this particular case.

>
>But the overall idea of handling crash hotplug support with
>crash dm-crypt looks good to me. So feel free to add:
>
>Reviewed-by: Sourabh Jain sourabhjain@linux.ibm.com

Thanks for reviewing and ack'ing the patch!

>
>Thanks,
>Sourabh Jain
>
>
>>  		goto unlock;
>>  	}
>>@@ -519,9 +519,9 @@ int crash_load_dm_crypt_keys(struct kimage *image)
>>  void kexec_file_post_load_cleanup_dm_crypt(struct kimage *image)
>>  {
>>  	/*
>>-	 * For CPU/memory hot-plugging, the kdump image will be reloaded. Prevent
>>-	 * keys_header from being cleaned up during unloading when
>>-	 * is_dm_key_reused=true
>>+	 * For CPU/memory hot-plugging without CONFIG_CRASH_HOTPLUG, the whole kdump
>>+	 * image will be reloaded. Prevent keys_header from being cleaned up during
>>+	 * unloading when is_dm_key_reused=true
>>  	 */
>>  	if (!is_dm_key_reused) {
>>  		kfree_sensitive(keys_header);
>>@@ -532,6 +532,11 @@ void kexec_file_post_load_cleanup_dm_crypt(struct kimage *image)
>>  		mutex_unlock(&config_keys_subsys.su_mutex);
>>  		mutex_acquired = false;
>>  	}
>>+
>>+#ifdef CONFIG_CRASH_HOTPLUG
>>+	if (image->hotplug_support)
>>+		image->dm_crypt_keys_addr = 0;
>>+#endif
>>  }
>>  static int __init configfs_dmcrypt_keys_init(void)
>

-- 
Best regards,
Coiby