To workaround or debug a split lock issue, the administrator may need to
disable or enable split lock detection during run time without rebooting
the system.
The interface /sys/device/system/cpu/split_lock_detect is added to allow
the administrator to disable or enable 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
Add an ABI document entry for /sys/devices/system/cpu/split_lock_detect.
Signed-off-by: Fenghua Yu <fenghua.yu@xxxxxxxxx>
---
Not sure if the justification for the sysfs knob is valid. If not, this
patch could be removed from this patch set.
.../ABI/testing/sysfs-devices-system-cpu | 22 ++++++++
arch/x86/kernel/cpu/intel.c | 52 ++++++++++++++++++-
2 files changed, 72 insertions(+), 2 deletions(-)
diff --git a/Documentation/ABI/testing/sysfs-devices-system-cpu b/Documentation/ABI/testing/sysfs-devices-system-cpu
index 9605dbd4b5b5..aad7b1698065 100644
--- a/Documentation/ABI/testing/sysfs-devices-system-cpu
+++ b/Documentation/ABI/testing/sysfs-devices-system-cpu
@@ -67,6 +67,28 @@ Description: Discover NUMA node a CPU belongs to
/sys/devices/system/cpu/cpu42/node2 -> ../../node/node2
+What: /sys/devices/system/cpu/split_lock_detect
+Date: March 2019
+Contact: Linux kernel mailing list <linux-kernel@xxxxxxxxxxxxxxx>
+Description: (RW) Control split lock detection on Intel Tremont and
+ future CPUs
+
+ Reads return split lock detection status:
+ 0: disabled
+ 1: enabled
+
+ Writes enable or disable split lock detection:
+ The first character is one of 'Nn0' or [oO][fF] for off
+ disables the feature.
+ The first character is one of 'Yy1' or [oO][nN] for on
+ enables the feature.
+
+ Please note the interface only shows or controls global setting.
+ During run time, split lock detection on one CPU may be
+ disabled if split lock operation in kernel code happens on
+ the CPU. The interface doesn't show or control split lock
+ detection on individual CPU.
+
What: /sys/devices/system/cpu/cpu#/topology/core_id
/sys/devices/system/cpu/cpu#/topology/core_siblings
/sys/devices/system/cpu/cpu#/topology/core_siblings_list
diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c
index 959ebf25beda..f257d1e92706 100644
--- a/arch/x86/kernel/cpu/intel.c
+++ b/arch/x86/kernel/cpu/intel.c
@@ -35,6 +35,7 @@
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;
/*
@@ -660,7 +661,7 @@ static void init_intel_misc_features(struct cpuinfo_x86 *c)
wrmsrl(MSR_MISC_FEATURES_ENABLES, msr);
}
-static void split_lock_update_msr(void)
+static void split_lock_update_msr(void *__unused)
{
if (split_lock_detect_enable) {
/* Enable split lock detection */
@@ -682,7 +683,7 @@ static void init_split_lock_detect(struct cpuinfo_x86 *c)
rdmsrl(MSR_TEST_CTL, test_ctl_val);
this_cpu_write(msr_test_ctl_cache, test_ctl_val);
- split_lock_update_msr();
+ split_lock_update_msr(NULL);
}
}
@@ -1114,3 +1115,50 @@ void handle_split_lock_kernel_mode(void)
this_cpu_and(msr_test_ctl_cache, ~TEST_CTL_SPLIT_LOCK_DETECT);
WARN_ONCE(1, "split lock operation detected\n");
}
+
+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);
+
+ if (split_lock_detect_enable)
+ pr_info("enabled\n");
+ else
+ pr_info("disabled\n");
+
+ 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
