[PATCH v9 13/17] x86/split_lock: Disable split lock detection by kernel parameter "nosplit_lock_detect"

[Fenghua Yu <fenghua.yu@xxxxxxxxx>]

To work around or debug split lock issues, the kernel parameter
"nosplit_lock_detect" is introduced to disable the feature during boot
time.

Signed-off-by: Fenghua Yu <fenghua.yu@xxxxxxxxx>
---
 .../admin-guide/kernel-parameters.txt         |  2 ++
 arch/x86/kernel/cpu/intel.c                   | 22 ++++++++++++++++---
 2 files changed, 21 insertions(+), 3 deletions(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 138f6664b2e2..bcf578a1bc77 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -3086,6 +3086,8 @@
 
 	nosoftlockup	[KNL] Disable the soft-lockup detector.
 
+	nosplit_lock_detect	[X86] Disable split lock detection
+
 	nosync		[HW,M68K] Disables sync negotiation for all devices.
 
 	nowatchdog	[KNL] Disable both lockup detectors, i.e.
diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c
index 4ccd890a45b0..4a854f051cf4 100644
--- a/arch/x86/kernel/cpu/intel.c
+++ b/arch/x86/kernel/cpu/intel.c
@@ -19,6 +19,7 @@
 #include <asm/microcode_intel.h>
 #include <asm/hwcap2.h>
 #include <asm/elf.h>
+#include <asm/cmdline.h>
 
 #ifdef CONFIG_X86_64
 #include <linux/topology.h>
@@ -34,6 +35,8 @@
 DEFINE_PER_CPU(u64, msr_test_ctl_cached);
 EXPORT_PER_CPU_SYMBOL_GPL(msr_test_ctl_cached);
 
+static bool split_lock_detect_enabled;
+
 /*
  * Just in case our CPU detection goes bad, or you have a weird system,
  * allow a way to override the automatic disabling of MPX.
@@ -629,8 +632,13 @@ static void init_intel_misc_features(struct cpuinfo_x86 *c)
 
 static void split_lock_update_msr(void)
 {
-	/* Enable split lock detection */
-	this_cpu_or(msr_test_ctl_cached, MSR_TEST_CTL_SPLIT_LOCK_DETECT);
+	if (split_lock_detect_enabled) {
+		/* Enable split lock detection */
+		this_cpu_or(msr_test_ctl_cached, MSR_TEST_CTL_SPLIT_LOCK_DETECT);
+	} else {
+		/* Disable split lock detection */
+		this_cpu_and(msr_test_ctl_cached, ~MSR_TEST_CTL_SPLIT_LOCK_DETECT);
+	}
 	wrmsrl(MSR_TEST_CTL, this_cpu_read(msr_test_ctl_cached));
 }
 
@@ -1027,7 +1035,15 @@ cpu_dev_register(intel_cpu_dev);
 static void __init split_lock_setup(void)
 {
 	setup_force_cpu_cap(X86_FEATURE_SPLIT_LOCK_DETECT);
-	pr_info("enabled\n");
+
+	if (cmdline_find_option_bool(boot_command_line,
+				     "nosplit_lock_detect")) {
+		split_lock_detect_enabled = false;
+		pr_info("disabled\n");
+	} else {
+		split_lock_detect_enabled = true;
+		pr_info("enabled\n");
+	}
 }
 
 void __init cpu_set_core_cap_bits(struct cpuinfo_x86 *c)
-- 
2.19.1