[PATCH v2 8/9] crash_dump: Disallow configfs/crash_dm_crypt_key/reuse if CONFIG_CRASH_HOTPLUG enabled

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

If CONFIG_CRASH_HOTPLUG is enabled, dm-crypt keys saved to reserved
memory will be took 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 CONFIG_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 |  9 ++++++---
 kernel/crash_dump_dm_crypt.c              | 14 +++++++++++---
 2 files changed, 17 insertions(+), 6 deletions(-)

diff --git a/Documentation/admin-guide/kdump/kdump.rst b/Documentation/admin-guide/kdump/kdump.rst
index 7587caadbae1..73f2e9500c60 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
@@ -593,7 +594,9 @@ with /sys/kernel/config/crash_dm_crypt_keys for setup,
 
     # To support CPU/memory hot-plugging, reuse keys already saved to reserved
     # memory
-    echo true > /sys/kernel/config/crash_dm_crypt_key/reuse
+    # Note if CONFIG_CRASH_HOTPLUG is enabled, this API is totally unnecessary
+    # thus will be disabled.
+    echo true > /sys/kernel/config/crash_dm_crypt_keys/reuse
 
 2. Load the dump-capture kernel
 
diff --git a/kernel/crash_dump_dm_crypt.c b/kernel/crash_dump_dm_crypt.c
index 36e51807d94f..7a7cae17f578 100644
--- a/kernel/crash_dump_dm_crypt.c
+++ b/kernel/crash_dump_dm_crypt.c
@@ -304,6 +304,11 @@ static ssize_t config_keys_reuse_store(struct config_item *item,
 	bool val;
 	int r;
 
+	if (IS_ENABLED(CONFIG_CRASH_HOTPLUG)) {
+		pr_info("CONFIG_CRASH_HOTPLUG already enabled");
+		return -EINVAL;
+	}
+
 	if (!kexec_crash_image || !kexec_crash_image->dm_crypt_keys_addr) {
 		pr_info("dm-crypt keys haven't be saved to crash-reserved memory\n");
 		return -EINVAL;
@@ -486,15 +491,18 @@ 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);
 		keys_header = NULL;
 	}
 
+	if (IS_ENABLED(CONFIG_CRASH_HOTPLUG))
+		image->dm_crypt_keys_addr = 0;
+
 	if (mutex_is_locked(&config_keys_subsys.su_mutex))
 		mutex_unlock(&config_keys_subsys.su_mutex);
 }
-- 
2.54.0