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 <[email protected]> --- 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 <[email protected]> +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
