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

[Sourabh Jain <sourabhjain@linux.ibm.com>]

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)