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

From: Like Xu
Date: Mon Sep 30 2019 - 19:28:04 EST


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