[PATCH v3 09/10] 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. 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