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

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

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