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Subject[PATCH v2 4/4] x86/split_lock: Disable #AC for split locked accesses
Date
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@intel.com>
---
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
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