[PATCH v7 15/21] x86/split_lock: Add a sysfs interface to enable/disable split lock detection during run time

[Fenghua Yu]

The interface /sys/device/system/cpu/split_lock_detect is added
to allow user to control split lock detection and show current split
lock detection setting.

Writing [yY1] or [oO][nN] to the file enables split lock detection and
writing [nN0] or [oO][fF] disables split lock detection. Split lock
detection is enabled or disabled on all CPUs.

Reading the file returns current global split lock detection setting:
0: disabled
1: enabled

Signed-off-by: Fenghua Yu <fenghua.yu@xxxxxxxxx>
---
 arch/x86/kernel/cpu/intel.c | 45 +++++++++++++++++++++++++++++++++++++
 1 file changed, 45 insertions(+)

diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c
index 6a692d215bef..f2c04aa36d78 100644
--- a/arch/x86/kernel/cpu/intel.c
+++ b/arch/x86/kernel/cpu/intel.c
@@ -34,6 +34,7 @@
 DEFINE_PER_CPU(u64, msr_test_ctl_cache);
 EXPORT_PER_CPU_SYMBOL_GPL(msr_test_ctl_cache);
 
+static DEFINE_MUTEX(split_lock_detect_mutex);
 static bool split_lock_detect_enable;
 
 /*
@@ -1097,3 +1098,47 @@ void __init cpu_set_core_cap_bits(struct cpuinfo_x86 *c)
 	if (ia32_core_cap & CORE_CAP_SPLIT_LOCK_DETECT)
 		set_split_lock_detect();
 }
+
+static ssize_t
+split_lock_detect_show(struct device *dev, struct device_attribute *attr,
+		       char *buf)
+{
+	return sprintf(buf, "%u\n", split_lock_detect_enable);
+}
+
+static ssize_t
+split_lock_detect_store(struct device *dev, struct device_attribute *attr,
+			const char *buf, size_t count)
+{
+	bool val;
+	int ret;
+
+	ret = strtobool(buf, &val);
+	if (ret)
+		return ret;
+
+	mutex_lock(&split_lock_detect_mutex);
+
+	split_lock_detect_enable = val;
+
+	/* Update the split lock detection setting in MSR on all online CPUs. */
+	on_each_cpu(split_lock_update_msr, NULL, 1);
+
+	show_split_lock_detection_info();
+
+	mutex_unlock(&split_lock_detect_mutex);
+
+	return count;
+}
+
+static DEVICE_ATTR_RW(split_lock_detect);
+
+static int __init split_lock_init(void)
+{
+	if (!boot_cpu_has(X86_FEATURE_SPLIT_LOCK_DETECT))
+		return -ENODEV;
+
+	return device_create_file(cpu_subsys.dev_root,
+				  &dev_attr_split_lock_detect);
+}
+subsys_initcall(split_lock_init);
-- 
2.19.1