[PATCH v9 09/14] x86/hotplug/keylocker: Ensure wrapping key backup capability

["Chang S. Bae" <chang.seok.bae@intel.com>]

To facilitate CPU hotplug, the wrapping key needs to be loaded during CPU
hotplug bringup. setup_keylocker() already establishes the routine
for the wakeup path by copying the key from the backup state.

Disable the feature if it's missing with CONFIG_HOTPLUG_CPU=y. Also,
update the code comment to indicate support for CPU hotplug.

Signed-off-by: Chang S. Bae <chang.seok.bae@intel.com>
Cc: Sangwhan Moon <sxm@google.com>
---
Changes from v8:
* Add as a new patch.
---
 arch/x86/kernel/keylocker.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kernel/keylocker.c b/arch/x86/kernel/keylocker.c
index d5d11d0263b7..1b57e11d93ad 100644
--- a/arch/x86/kernel/keylocker.c
+++ b/arch/x86/kernel/keylocker.c
@@ -69,6 +69,8 @@ static bool copy_keylocker(void)
  * On wakeup, APs copy a wrapping key after the boot CPU verifies a valid
  * backup status through restore_keylocker(). Subsequently, they adhere
  * to the error handling protocol by invalidating the flag.
+ *
+ * This setup routine is also invoked in the hotplug bringup path.
  */
 void setup_keylocker(void)
 {
@@ -135,11 +137,11 @@ static int __init init_keylocker(void)
 
 	/*
 	 * The backup is critical for restoring the wrapping key upon
-	 * wakeup.
+	 * wakeup or during hotplug bringup.
 	 */
 	backup_available = !!(ebx & KEYLOCKER_CPUID_EBX_BACKUP);
-	if (!backup_available && IS_ENABLED(CONFIG_SUSPEND)) {
-		pr_debug("x86/keylocker: No key backup with possible S3/4.\n");
+	if (!backup_available && (IS_ENABLED(CONFIG_SUSPEND) || IS_ENABLED(CONFIG_HOTPLUG_CPU))) {
+		pr_debug("x86/keylocker: No key backup with possible S3/4 or CPU hotplug.\n");
 		goto clear_cap;
 	}
 
-- 
2.34.1