[PATCH 1/3] perf/core: Provide a kernel-internal interface to recalibrate event period

[Like Xu <like.xu@xxxxxxxxxxxxxxx>]

Currently, perf_event_period() is used by user tool via ioctl. Exporting
perf_event_period() for kernel users (such as KVM) who may recalibrate the
event period for their assigned counters according to their requirements.

The perf_event_period() is an external accessor, just like the
perf_event_{en,dis}able() and should thus use perf_event_ctx_lock().

Suggested-by: Kan Liang <kan.liang@xxxxxxxxxxxxxxx>
Reviewed-by: Kan Liang <kan.liang@xxxxxxxxxxxxxxx>
Signed-off-by: Like Xu <like.xu@xxxxxxxxxxxxxxx>
---
 include/linux/perf_event.h |  5 +++++
 kernel/events/core.c       | 28 +++++++++++++++++++++-------
 2 files changed, 26 insertions(+), 7 deletions(-)

diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 61448c19a132..83db24173e4d 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -1336,6 +1336,7 @@ extern void perf_event_disable_local(struct perf_event *event);
 extern void perf_event_disable_inatomic(struct perf_event *event);
 extern void perf_event_task_tick(void);
 extern int perf_event_account_interrupt(struct perf_event *event);
+extern int perf_event_period(struct perf_event *event, u64 value);
 #else /* !CONFIG_PERF_EVENTS: */
 static inline void *
 perf_aux_output_begin(struct perf_output_handle *handle,
@@ -1415,6 +1416,10 @@ static inline void perf_event_disable(struct perf_event *event)		{ }
 static inline int __perf_event_disable(void *info)			{ return -1; }
 static inline void perf_event_task_tick(void)				{ }
 static inline int perf_event_release_kernel(struct perf_event *event)	{ return 0; }
+extern int perf_event_period(struct perf_event *event, u64 value)
+{
+	return -EINVAL;
+}
 #endif
 
 #if defined(CONFIG_PERF_EVENTS) && defined(CONFIG_CPU_SUP_INTEL)
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 4655adbbae10..de740d20b028 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -5094,16 +5094,11 @@ static int perf_event_check_period(struct perf_event *event, u64 value)
 	return event->pmu->check_period(event, value);
 }
 
-static int perf_event_period(struct perf_event *event, u64 __user *arg)
+static int _perf_event_period(struct perf_event *event, u64 value)
 {
-	u64 value;
-
 	if (!is_sampling_event(event))
 		return -EINVAL;
 
-	if (copy_from_user(&value, arg, sizeof(value)))
-		return -EFAULT;
-
 	if (!value)
 		return -EINVAL;
 
@@ -5121,6 +5116,19 @@ static int perf_event_period(struct perf_event *event, u64 __user *arg)
 	return 0;
 }
 
+int perf_event_period(struct perf_event *event, u64 value)
+{
+	struct perf_event_context *ctx;
+	int ret;
+
+	ctx = perf_event_ctx_lock(event);
+	ret = _perf_event_period(event, value);
+	perf_event_ctx_unlock(event, ctx);
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(perf_event_period);
+
 static const struct file_operations perf_fops;
 
 static inline int perf_fget_light(int fd, struct fd *p)
@@ -5164,8 +5172,14 @@ static long _perf_ioctl(struct perf_event *event, unsigned int cmd, unsigned lon
 		return _perf_event_refresh(event, arg);
 
 	case PERF_EVENT_IOC_PERIOD:
-		return perf_event_period(event, (u64 __user *)arg);
+	{
+		u64 value;
+
+		if (get_user(value, (u64 __user *)&arg))
+			return -EFAULT;
 
+		return _perf_event_period(event, value);
+	}
 	case PERF_EVENT_IOC_ID:
 	{
 		u64 id = primary_event_id(event);
-- 
2.21.0