[RFC 2/2] drm/i915/pmu: Allow fine-grained PMU access control

[Tvrtko Ursulin <tursulin@ursulin.net>]

From: Tvrtko Ursulin <tvrtko.ursulin@intel.com>

We implement the new pmu->is_privileged callback and add our own sysctl
as /proc/sys/dev/i915/pmu_stream_paranoid (defaulting to true), which
enables system administrators to override the global
/proc/sys/kernel/perf_event_paranoid setting for i915 PMU only.

Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: Dmitry Rogozhkin <dmitry.v.rogozhkin@intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/i915_pmu.c | 55 +++++++++++++++++++++++++++++++++++++++--
 drivers/gpu/drm/i915/i915_pmu.h |  4 +++
 2 files changed, 57 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_pmu.c b/drivers/gpu/drm/i915/i915_pmu.c
index baa663641bb7..a8eca7303b7e 100644
--- a/drivers/gpu/drm/i915/i915_pmu.c
+++ b/drivers/gpu/drm/i915/i915_pmu.c
@@ -43,6 +43,11 @@
 
 static cpumask_t i915_pmu_cpumask = CPU_MASK_NONE;
 
+/* for sysctl proc_dointvec_minmax of dev.i915.pmu_stream_paranoid */
+static int zero;
+static int one = 1;
+static u32 i915_pmu_stream_paranoid = true;
+
 static u8 engine_config_sample(u64 config)
 {
 	return config & I915_PMU_SAMPLE_MASK;
@@ -647,6 +652,11 @@ static int i915_pmu_event_event_idx(struct perf_event *event)
 	return 0;
 }
 
+static bool i915_pmu_is_privileged(struct perf_event *event)
+{
+	return i915_pmu_stream_paranoid;
+}
+
 static ssize_t i915_pmu_format_show(struct device *dev,
 				    struct device_attribute *attr, char *buf)
 {
@@ -834,11 +844,44 @@ static void i915_pmu_unregister_cpuhp_state(struct drm_i915_private *i915)
 #endif
 }
 
+static struct ctl_table pmu_table[] = {
+	{
+		.procname = "pmu_stream_paranoid",
+		.data = &i915_pmu_stream_paranoid,
+		.maxlen = sizeof(i915_pmu_stream_paranoid),
+		.mode = 0644,
+		.proc_handler = proc_dointvec_minmax,
+		.extra1 = &zero,
+		.extra2 = &one,
+	},
+	{}
+};
+
+static struct ctl_table i915_root[] = {
+	{
+		.procname = "i915",
+		.maxlen = 0,
+		.mode = 0555,
+		.child = pmu_table,
+	},
+	{}
+};
+
+static struct ctl_table dev_root[] = {
+	{
+		.procname = "dev",
+		.maxlen = 0,
+		.mode = 0555,
+		.child = i915_root,
+	},
+	{}
+};
+
 void i915_pmu_register(struct drm_i915_private *i915)
 {
 	struct intel_engine_cs *engine;
 	enum intel_engine_id id;
-	int ret;
+	int ret = -EINVAL;
 
 	if (INTEL_GEN(i915) <= 2) {
 		DRM_INFO("PMU not supported for this GPU.");
@@ -854,6 +897,7 @@ void i915_pmu_register(struct drm_i915_private *i915)
 	i915->pmu.base.stop		= i915_pmu_event_stop;
 	i915->pmu.base.read		= i915_pmu_event_read;
 	i915->pmu.base.event_idx	= i915_pmu_event_event_idx;
+	i915->pmu.base.is_privileged	= i915_pmu_is_privileged;
 
 	spin_lock_init(&i915->pmu.lock);
 	hrtimer_init(&i915->pmu.timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
@@ -863,9 +907,12 @@ void i915_pmu_register(struct drm_i915_private *i915)
 		INIT_DELAYED_WORK(&engine->pmu.disable_busy_stats,
 				  __disable_busy_stats);
 
+	if (!(i915->pmu.sysctl_header = register_sysctl_table(dev_root)))
+		goto err;
+
 	ret = perf_pmu_register(&i915->pmu.base, "i915", -1);
 	if (ret)
-		goto err;
+		goto err_pmu;
 
 	ret = i915_pmu_register_cpuhp_state(i915);
 	if (ret)
@@ -875,6 +922,8 @@ void i915_pmu_register(struct drm_i915_private *i915)
 
 err_unreg:
 	perf_pmu_unregister(&i915->pmu.base);
+err_pmu:
+	unregister_sysctl_table(i915->pmu.sysctl_header);
 err:
 	i915->pmu.base.event_init = NULL;
 	DRM_NOTE("Failed to register PMU! (err=%d)\n", ret);
@@ -899,6 +948,8 @@ void i915_pmu_unregister(struct drm_i915_private *i915)
 
 	i915_pmu_unregister_cpuhp_state(i915);
 
+	unregister_sysctl_table(i915->pmu.sysctl_header);
+
 	perf_pmu_unregister(&i915->pmu.base);
 	i915->pmu.base.event_init = NULL;
 }
diff --git a/drivers/gpu/drm/i915/i915_pmu.h b/drivers/gpu/drm/i915/i915_pmu.h
index e209783a4c5f..30e2192b4218 100644
--- a/drivers/gpu/drm/i915/i915_pmu.h
+++ b/drivers/gpu/drm/i915/i915_pmu.h
@@ -61,6 +61,10 @@ struct i915_pmu {
 	 * @timer: Timer for internal i915 PMU sampling.
 	 */
 	struct hrtimer timer;
+	/**
+	 * @sysctl_header: Sysctl table header.
+	 */
+	struct ctl_table_header *sysctl_header;
 	/**
 	 * @enable: Bitmask of all currently enabled events.
 	 *
-- 
2.14.1