[PATCH v2 4/4] x86/split_lock: Disable #AC for split locked accesses

[Fenghua Yu]

By default, #AC for split lock is enabled. In some cases (e.g. system
hang when firmware hits split lock), user may want to opt-out of the
feature.

Kernel parameter "ac_split_lock_off" disables the feature during boot time.

Signed-off-by: Fenghua Yu <fenghua.yu@xxxxxxxxx>
---
 Documentation/admin-guide/kernel-parameters.txt | 4 ++++
 arch/x86/kernel/cpu/test_ctl.c                  | 9 +++++++++
 2 files changed, 13 insertions(+)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index efc7aa7a0670..7bf3b37dccdb 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -4086,6 +4086,10 @@
 	spia_pedr=
 	spia_peddr=
 
+	ac_split_lock_off [X86]
+			Disable #AC exception for split locked accesses.
+			By default, this feature is enabled in kernel.
+
 	srcutree.counter_wrap_check [KNL]
 			Specifies how frequently to check for
 			grace-period sequence counter wrap for the
diff --git a/arch/x86/kernel/cpu/test_ctl.c b/arch/x86/kernel/cpu/test_ctl.c
index f12e8b24215d..4e6ed267e8b7 100644
--- a/arch/x86/kernel/cpu/test_ctl.c
+++ b/arch/x86/kernel/cpu/test_ctl.c
@@ -85,3 +85,12 @@ void setup_ac_split_lock(void)
 		pr_info_once("#AC for split lock is disabled\n");
 	}
 }
+
+static __init int ac_split_lock_off(char *str)
+{
+	enable_ac_split_lock = false;
+
+	return 0;
+}
+
+early_param("ac_split_lock_off", ac_split_lock_off);
-- 
2.5.0