perf/x86: add sysfs entry to freeze counter on SMI

From: Kan Liang <[email protected]>

Currently, the SMIs are visible to all performance counters. Because many users want to measure everything including SMIs. But in some cases, the SMI cycles should not be count. For example, to calculate the cost of SMI itself. So a knob is needed.

When setting FREEZE_WHILE_SMM bit in IA32_DEBUGCTL, all performance counters will be effected. There is no way to do per-counter freeze on SMI. So it should not use the per-event interface (e.g. ioctl or event attribute) to set FREEZE_WHILE_SMM bit.

Adds sysfs entry /sys/device/cpu/freeze_on_smi to set FREEZE_WHILE_SMM bit in IA32_DEBUGCTL. When set, freezes perfmon and trace messages while in SMM.
Value has to be 0 or 1. It will be applied to all processors. Also serialize the entire setting so we don't get multiple concurrent threads trying to update to different values.

Signed-off-by Kan Liang <[email protected]>

---

why do we need an open coded version of __flip_bit() instead of reusing that?
- msr_set_bit/msr_clear_bit is enough for our requirement. There is no extra work needed.
__flip_bit is static inline. It cannot be used directly. If we expose it, there will be two sets of interfaces to flip MSR bit. I think it's too much.

Changes since V6:
- fix sprintf warnning. Sorry for the noise.

Changes since V5:
- Don't force unsigned long to bool. That will be a problem on LE machines.

Changes since V4:
- drop msr_flip_bit function
- Use on_each_cpu() which already include all the needed protection
- Some small changes according to the comments

 arch/x86/events/core.c           | 10 +++++++
 arch/x86/events/intel/core.c     | 63
++++++++++++++++++++++++++++++++++++++++
 arch/x86/events/perf_event.h     |  3 ++
 arch/x86/include/asm/msr-index.h |  2 ++
 4 files changed, 78 insertions(+)

arch/x86/events/core.c +2 -0

index 580b60f..e6f5e4b 100644
@@ -1750,6 +1750,8 @@ ssize_t x86_event_sysfs_show(char *page, u64
 config, u64 event)
 	return ret;
 }
 
+static struct attribute_group x86_pmu_attr_group;
+
 static int __init init_hw_perf_events(void)
 {

arch/x86/events/core.c +8 -0

 	struct x86_pmu_quirk *quirk;

@@ -1813,6 +1815,14 @@ static int __init init_hw_perf_events(void)
 			x86_pmu_events_group.attrs = tmp;
 	}
 
+	if (x86_pmu.attrs) {
+		struct attribute **tmp;
+
+		tmp = merge_attr(x86_pmu_attr_group.attrs, x86_pmu.attrs);
+		if (!WARN_ON(!tmp))
+			x86_pmu_attr_group.attrs = tmp;
+	}
+
 	pr_info("... version:                %d\n",     x86_pmu.version);
 	pr_info("... bit width:              %d\n",     x86_pmu.cntval_bits);
 	pr_info("... generic registers:      %d\n",     x86_pmu.num_counters);

arch/x86/events/intel/core.c +63 -0

index a6d91d4..da9047e 100644
@@ -3160,6 +3160,19 @@ static int intel_pmu_cpu_prepare(int cpu)
 	return -ENOMEM;
 }
 
+static void flip_smm_bit(void *data)
+{
+	unsigned long set = *(unsigned long *)data;
+
+	if (set > 0) {
+		msr_set_bit(MSR_IA32_DEBUGCTLMSR,
+			    DEBUGCTLMSR_FREEZE_IN_SMM_BIT);
+	} else {
+		msr_clear_bit(MSR_IA32_DEBUGCTLMSR,
+			      DEBUGCTLMSR_FREEZE_IN_SMM_BIT);
+	}
+}
+
 static void intel_pmu_cpu_starting(int cpu)
 {
 	struct cpu_hw_events *cpuc = &per_cpu(cpu_hw_events, cpu);

@@ -3174,6 +3187,8 @@ static void intel_pmu_cpu_starting(int cpu)
 
 	cpuc->lbr_sel = NULL;
 
+	flip_smm_bit(&x86_pmu.attr_freeze_on_smi);
+
 	if (!cpuc->shared_regs)
 		return;
 

@@ -3595,6 +3610,52 @@ static struct attribute *hsw_events_attrs[] = {
 	NULL
 };
 
+static ssize_t freeze_on_smi_show(struct device *cdev,
+				  struct device_attribute *attr,
+				  char *buf)
+{
+	return sprintf(buf, "%lu\n", x86_pmu.attr_freeze_on_smi);
+}
+
+static DEFINE_MUTEX(freeze_on_smi_mutex);
+
+static ssize_t freeze_on_smi_store(struct device *cdev,
+				   struct device_attribute *attr,
+				   const char *buf, size_t count)
+{
+	unsigned long val;
+	ssize_t ret;
+
+	ret = kstrtoul(buf, 0, &val);
+	if (ret)
+		return ret;
+
+	if (val > 1)
+		return -EINVAL;
+
+	mutex_lock(&freeze_on_smi_mutex);
+
+	if (x86_pmu.attr_freeze_on_smi == val)
+		goto done;
+
+	x86_pmu.attr_freeze_on_smi = val;
+
+	get_online_cpus();
+	on_each_cpu(flip_smm_bit, &val, 1);
+	put_online_cpus();
+done:
+	mutex_unlock(&freeze_on_smi_mutex);
+
+	return count;
+}
+
+static DEVICE_ATTR_RW(freeze_on_smi);
+
+static struct attribute *intel_pmu_attrs[] = {
+	&dev_attr_freeze_on_smi.attr,
+	NULL,
+};
+
 __init int intel_pmu_init(void)
 {
 	union cpuid10_edx edx;

@@ -3641,6 +3702,8 @@ __init int intel_pmu_init(void)
 
 	x86_pmu.max_pebs_events		= min_t(unsigned,
 MAX_PEBS_EVENTS, x86_pmu.num_counters);
 
+
+	x86_pmu.attrs			= intel_pmu_attrs;
 	/*
 	 * Quirk: v2 perfmon does not report fixed-purpose events, so

arch/x86/events/intel/core.c +0 -0

 	 * assume at least 3 events, when not running in a hypervisor:

arch/x86/events/perf_event.h +3 -0

index be3d362..53728ee 100644
@@ -562,6 +562,9 @@ struct x86_pmu {
 	ssize_t		(*events_sysfs_show)(char *page, u64 config);
 	struct attribute **cpu_events;
 
+	unsigned long	attr_freeze_on_smi;
+	struct attribute **attrs;
+
 	/*
 	 * CPU Hotplug hooks
 	 */

arch/x86/include/asm/msr- renamed from arch/x86/include/asm/msr-index.h +0 -0

index.h
index 673f9ac..18b1623 100644

arch/x86/include/asm/msr-index.h +2 -1

@@ -137,6 +137,8 @@
 #define DEBUGCTLMSR_BTS_OFF_OS		(1UL <<  9)
 #define DEBUGCTLMSR_BTS_OFF_USR		(1UL << 10)
 #define DEBUGCTLMSR_FREEZE_LBRS_ON_PMI	(1UL << 11)
+#define DEBUGCTLMSR_FREEZE_IN_SMM_BIT	14
+#define DEBUGCTLMSR_FREEZE_IN_SMM	(1UL <<
 DEBUGCTLMSR_FREEZE_IN_SMM_BIT)
 
 #define MSR_PEBS_FRONTEND		0x000003f7
 
--

2.7.4

From: Kan Liang <[email protected]>

Currently, the SMIs are visible to all performance counters. Because many users want to measure everything including SMIs. But in some cases, the SMI cycles should not be count. For example, to calculate the cost of SMI itself. So a knob is needed.

When setting FREEZE_WHILE_SMM bit in IA32_DEBUGCTL, all performance counters will be effected. There is no way to do per-counter freeze on SMI. So it should not use the per-event interface (e.g. ioctl or event attribute) to set FREEZE_WHILE_SMM bit.

Adds sysfs entry /sys/device/cpu/freeze_on_smi to set FREEZE_WHILE_SMM bit in IA32_DEBUGCTL. When set, freezes perfmon and trace messages while in SMM.
Value has to be 0 or 1. It will be applied to all processors. Also serialize the entire setting so we don't get multiple concurrent threads trying to update to different values.

Signed-off-by Kan Liang <[email protected]>