[PATCH v2 3/3] x86/umwait: Control umwait maximum time

[Fenghua Yu <fenghua.yu@intel.com>]

IA32_UMWAIT_CONTROL[31:2] determines the maximum time in TSC-quanta
that processor can stay in C0.1 or C0.2.

The maximum time value in IA32_UMWAIT_CONTROL[31-2] is set as zero which
means there is no global time limit for UMWAIT and TPAUSE instructions.
Each process sets its own umwait maximum time as the instructions operand.

User can specify global umwait maximum time through interface:
/sys/devices/system/cpu/umwait_control/umwait_max_time
The value in the interface is in decimal in TSC-quanta. Bits[1:0]
are cleared when the value is stored.

Signed-off-by: Fenghua Yu <fenghua.yu@intel.com>
---
 arch/x86/include/asm/msr-index.h |  2 ++
 arch/x86/power/umwait.c          | 42 +++++++++++++++++++++++++++++++-
 2 files changed, 43 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/msr-index.h b/arch/x86/include/asm/msr-index.h
index b56bfecae0de..42b9104fc15b 100644
--- a/arch/x86/include/asm/msr-index.h
+++ b/arch/x86/include/asm/msr-index.h
@@ -62,6 +62,8 @@
 #define MSR_IA32_UMWAIT_CONTROL		0xe1
 #define UMWAIT_CONTROL_C02_BIT		0x0
 #define UMWAIT_CONTROL_C02_MASK		0x00000001
+#define UMWAIT_CONTROL_MAX_TIME_BIT	0x2
+#define UMWAIT_CONTROL_MAX_TIME_MASK	0xfffffffc
 
 #define MSR_PKG_CST_CONFIG_CONTROL	0x000000e2
 #define NHM_C3_AUTO_DEMOTE		(1UL << 25)
diff --git a/arch/x86/power/umwait.c b/arch/x86/power/umwait.c
index 95b3867aac1e..4a1a507d3bb7 100644
--- a/arch/x86/power/umwait.c
+++ b/arch/x86/power/umwait.c
@@ -10,6 +10,7 @@
 #include <asm/msr.h>
 
 static int umwait_enable_c0_2 = 1; /* 0: disable C0.2. 1: enable C0.2. */
+static u32 umwait_max_time; /* In TSC-quanta. Only bits [31:2] are used. */
 static DEFINE_MUTEX(umwait_lock);
 
 /* Return value that will be used to set umwait control MSR */
@@ -20,7 +21,8 @@ static inline u32 umwait_control_val(void)
 	 * When bit 0 is 1, C0.2 is disabled. Otherwise, C0.2 is enabled.
 	 * So value in bit 0 is opposite of umwait_enable_c0_2.
 	 */
-	return ~umwait_enable_c0_2 & UMWAIT_CONTROL_C02_MASK;
+	return (~umwait_enable_c0_2 & UMWAIT_CONTROL_C02_MASK) |
+	       umwait_max_time;
 }
 
 static ssize_t umwait_enable_c0_2_show(struct device *dev,
@@ -61,8 +63,46 @@ static ssize_t umwait_enable_c0_2_store(struct device *dev,
 
 static DEVICE_ATTR_RW(umwait_enable_c0_2);
 
+static ssize_t umwait_max_time_show(struct device *kobj,
+				    struct device_attribute *attr, char *buf)
+{
+	return sprintf(buf, "%u\n", umwait_max_time);
+}
+
+static ssize_t umwait_max_time_store(struct device *kobj,
+				     struct device_attribute *attr,
+				     const char *buf, size_t count)
+{
+	u32 msr_val, max_time;
+	int cpu, ret;
+
+	ret = kstrtou32(buf, 10, &max_time);
+	if (ret)
+		return ret;
+
+	mutex_lock(&umwait_lock);
+
+	/* Only get max time value from bits [31:2] */
+	max_time &= UMWAIT_CONTROL_MAX_TIME_MASK;
+	/* Update the max time value in memory */
+	umwait_max_time = max_time;
+	msr_val = umwait_control_val();
+	get_online_cpus();
+	/* All CPUs have same umwait max time */
+	for_each_online_cpu(cpu)
+		wrmsr_on_cpu(cpu, MSR_IA32_UMWAIT_CONTROL, msr_val, 0);
+	put_online_cpus();
+
+	mutex_unlock(&umwait_lock);
+
+	return count;
+}
+
+static DEVICE_ATTR_RW(umwait_max_time);
+
 static struct attribute *umwait_attrs[] = {
 	&dev_attr_umwait_enable_c0_2.attr,
+	&dev_attr_umwait_max_time.attr,
 	NULL
 };
 
-- 
2.19.1