[PATCH v7 14/21] x86/split_lock: Enable split lock detection by default

[Fenghua Yu]

A split locked access locks bus and degrades overall memory access
performance. When split lock detection feature is enumerated, enable
the feature by default to find any split lock issue.

Signed-off-by: Fenghua Yu <fenghua.yu@xxxxxxxxx>
---
 arch/x86/kernel/cpu/intel.c | 34 ++++++++++++++++++++++++++++++++++
 1 file changed, 34 insertions(+)

diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c
index 997d683d3c27..6a692d215bef 100644
--- a/arch/x86/kernel/cpu/intel.c
+++ b/arch/x86/kernel/cpu/intel.c
@@ -34,6 +34,8 @@
 DEFINE_PER_CPU(u64, msr_test_ctl_cache);
 EXPORT_PER_CPU_SYMBOL_GPL(msr_test_ctl_cache);
 
+static bool split_lock_detect_enable;
+
 /*
  * Just in case our CPU detection goes bad, or you have a weird system,
  * allow a way to override the automatic disabling of MPX.
@@ -164,6 +166,23 @@ static bool bad_spectre_microcode(struct cpuinfo_x86 *c)
 	return false;
 }
 
+static void split_lock_update_msr(void *__unused)
+{
+	if (split_lock_detect_enable) {
+		msr_set_bit(MSR_TEST_CTL, TEST_CTL_SPLIT_LOCK_DETECT_SHIFT);
+		this_cpu_or(msr_test_ctl_cache, TEST_CTL_SPLIT_LOCK_DETECT);
+	} else {
+		msr_clear_bit(MSR_TEST_CTL, TEST_CTL_SPLIT_LOCK_DETECT_SHIFT);
+		this_cpu_and(msr_test_ctl_cache, ~TEST_CTL_SPLIT_LOCK_DETECT);
+	}
+}
+
+static void init_split_lock_detect(struct cpuinfo_x86 *c)
+{
+	if (cpu_has(c, X86_FEATURE_SPLIT_LOCK_DETECT))
+		split_lock_update_msr(NULL);
+}
+
 static void early_init_intel(struct cpuinfo_x86 *c)
 {
 	u64 misc_enable;
@@ -661,6 +680,8 @@ static void init_intel(struct cpuinfo_x86 *c)
 {
 	early_init_intel(c);
 
+	init_split_lock_detect(c);
+
 	intel_workarounds(c);
 
 	/*
@@ -1032,9 +1053,22 @@ static const struct cpu_dev intel_cpu_dev = {
 
 cpu_dev_register(intel_cpu_dev);
 
+#undef pr_fmt
+#define pr_fmt(fmt) "x86/split lock detection: " fmt
+
+static void show_split_lock_detection_info(void)
+{
+	if (split_lock_detect_enable)
+		pr_info("enabled\n");
+	else
+		pr_info("disabled\n");
+}
+
 static void __init set_split_lock_detect(void)
 {
 	setup_force_cpu_cap(X86_FEATURE_SPLIT_LOCK_DETECT);
+	split_lock_detect_enable = true;
+	show_split_lock_detection_info();
 }
 
 void __init cpu_set_core_cap_bits(struct cpuinfo_x86 *c)
-- 
2.19.1