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

[PATCH v3 09/10] 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. 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;
+#else
+	return false;
+#endif
+}
+
 static ssize_t config_keys_reuse_store(struct config_item *item,
 					   const char *page, size_t count)
 {
@@ -317,6 +326,11 @@ static ssize_t config_keys_reuse_store(struct config_item *item,
 	bool val;
 	int r;
 
+	if (kexec_crash_image && crash_hotplug_support(kexec_crash_image)) {
+		pr_debug("Crash hotplug supported\n");
+		return -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");
 		return -EINVAL;
@@ -513,9 +527,9 @@ 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);
@@ -526,6 +540,9 @@ void kexec_file_post_load_cleanup_dm_crypt(struct kimage *image)
 		mutex_unlock(&config_keys_subsys.su_mutex);
 		mutex_acquired = false;
 	}
+
+	if (crash_hotplug_support(image))
+		image->dm_crypt_keys_addr = 0;
 }
 
 static int __init configfs_dmcrypt_keys_init(void)
-- 
2.55.0

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

[Sourabh Jain]

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.

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

- Sourabh Jain

> +#else
> +	return false;
> +#endif
> +}
> +
>   static ssize_t config_keys_reuse_store(struct config_item *item,
>   					   const char *page, size_t count)
>   {
> @@ -317,6 +326,11 @@ static ssize_t config_keys_reuse_store(struct config_item *item,
>   	bool val;
>   	int r;
>   
> +	if (kexec_crash_image && crash_hotplug_support(kexec_crash_image)) {
> +		pr_debug("Crash hotplug supported\n");
> +		return -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");
>   		return -EINVAL;
> @@ -513,9 +527,9 @@ 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);
> @@ -526,6 +540,9 @@ void kexec_file_post_load_cleanup_dm_crypt(struct kimage *image)
>   		mutex_unlock(&config_keys_subsys.su_mutex);
>   		mutex_acquired = false;
>   	}
> +
> +	if (crash_hotplug_support(image))
> +		image->dm_crypt_keys_addr = 0;
>   }
>   
>   static int __init configfs_dmcrypt_keys_init(void)

Re: [PATCH v3 10/10] Documentation: kdump: Add arm64 and ppc64le to encrypted dump target support list

[Sourabh Jain]

On 29/07/26 09:06, Coiby Xu wrote:
> 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>
> 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

Changes look good to me. Feel free to add.

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

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

[Coiby Xu]

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