drm/i915: Add dev.i915.perf_stream_paranoid sysctl option

Consistent with the kernel.perf_event_paranoid sysctl option that can
allow non-root users to access system wide cpu metrics, this can
optionally allow non-root users to access system wide OA counter metrics
from Gen graphics hardware.

Signed-off-by: Robert Bragg <robert@sixbynine.org>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Reviewed-by: Sourab Gupta <sourab.gupta@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/20161107194957.3385-9-robert@sixbynine.org

drivers/gpu/drm/i915/i915_drv.h

@@ -2194,6 +2194,7 @@ struct drm_i915_private {
 		bool initialized;
 
 		struct kobject *metrics_kobj;
+		struct ctl_table_header *sysctl_header;
 
 		struct mutex lock;
 		struct list_head streams;

drivers/gpu/drm/i915/i915_perf.c

@@ -64,6 +64,11 @@
 #define POLL_FREQUENCY 200
 #define POLL_PERIOD (NSEC_PER_SEC / POLL_FREQUENCY)
 
+/* for sysctl proc_dointvec_minmax of dev.i915.perf_stream_paranoid */
+static int zero;
+static int one = 1;
+static u32 i915_perf_stream_paranoid = true;
+
 /* The maximum exponent the hardware accepts is 63 (essentially it selects one
  * of the 64bit timestamp bits to trigger reports from) but there's currently
  * no known use case for sampling as infrequently as once per 47 thousand years.
@@ -1207,7 +1212,13 @@ i915_perf_open_ioctl_locked(struct drm_i915_private *dev_priv,
 		}
 	}
 
-	if (!specific_ctx && !capable(CAP_SYS_ADMIN)) {
+	/* Similar to perf's kernel.perf_paranoid_cpu sysctl option
+	 * we check a dev.i915.perf_stream_paranoid sysctl option
+	 * to determine if it's ok to access system wide OA counters
+	 * without CAP_SYS_ADMIN privileges.
+	 */
+	if (!specific_ctx &&
+	    i915_perf_stream_paranoid && !capable(CAP_SYS_ADMIN)) {
 		DRM_ERROR("Insufficient privileges to open system-wide i915 perf stream\n");
 		ret = -EACCES;
 		goto err_ctx;
@@ -1460,6 +1471,39 @@ void i915_perf_unregister(struct drm_i915_private *dev_priv)
 	dev_priv->perf.metrics_kobj = NULL;
 }
 
+static struct ctl_table oa_table[] = {
+	{
+	 .procname = "perf_stream_paranoid",
+	 .data = &i915_perf_stream_paranoid,
+	 .maxlen = sizeof(i915_perf_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 = oa_table,
+	 },
+	{}
+};
+
+static struct ctl_table dev_root[] = {
+	{
+	 .procname = "dev",
+	 .maxlen = 0,
+	 .mode = 0555,
+	 .child = i915_root,
+	 },
+	{}
+};
+
 void i915_perf_init(struct drm_i915_private *dev_priv)
 {
 	if (!IS_HASWELL(dev_priv))
@@ -1490,6 +1534,8 @@ void i915_perf_init(struct drm_i915_private *dev_priv)
 	dev_priv->perf.oa.n_builtin_sets =
 		i915_oa_n_builtin_metric_sets_hsw;
 
+	dev_priv->perf.sysctl_header = register_sysctl_table(dev_root);
+
 	dev_priv->perf.initialized = true;
 }
 
@@ -1498,6 +1544,8 @@ void i915_perf_fini(struct drm_i915_private *dev_priv)
 	if (!dev_priv->perf.initialized)
 		return;
 
+	unregister_sysctl_table(dev_priv->perf.sysctl_header);
+
 	memset(&dev_priv->perf.oa.ops, 0, sizeof(dev_priv->perf.oa.ops));
 	dev_priv->perf.initialized = false;
 }