[PATCH 7/9] drm/i915: Add dev.i915.perf_event_paranoid sysctl option

[Robert Bragg <robert@sixbynine.org>]

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>
---
 drivers/gpu/drm/i915/i915_drv.h  |  1 +
 drivers/gpu/drm/i915/i915_perf.c | 46 +++++++++++++++++++++++++++++++++++++++-
 2 files changed, 46 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 1406b93..2ac32b2 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -2081,6 +2081,7 @@ struct drm_i915_private {
 		bool initialized;
 
 		struct kobject *metrics_kobj;
+		struct ctl_table_header *sysctl_header;
 
 		struct mutex lock;
 		struct list_head streams;
diff --git a/drivers/gpu/drm/i915/i915_perf.c b/drivers/gpu/drm/i915/i915_perf.c
index f2db3de..c2ba16a 100644
--- a/drivers/gpu/drm/i915/i915_perf.c
+++ b/drivers/gpu/drm/i915/i915_perf.c
@@ -59,6 +59,8 @@
 #define POLL_FREQUENCY 200
 #define POLL_PERIOD (NSEC_PER_SEC / POLL_FREQUENCY)
 
+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.
@@ -1105,7 +1107,13 @@ int i915_perf_open_ioctl_locked(struct drm_device *dev,
 		}
 	}
 
-	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;
@@ -1309,6 +1317,38 @@ int i915_perf_open_ioctl(struct drm_device *dev, void *data,
 	return ret;
 }
 
+
+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,
+	 },
+	{}
+};
+
+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_device *dev)
 {
 	struct drm_i915_private *dev_priv = to_i915(dev);
@@ -1354,6 +1394,8 @@ void i915_perf_init(struct drm_device *dev)
 		return;
 	}
 
+	dev_priv->perf.sysctl_header = register_sysctl_table(dev_root);
+
 	dev_priv->perf.initialized = true;
 
 	return;
@@ -1366,6 +1408,8 @@ void i915_perf_fini(struct drm_device *dev)
 	if (!dev_priv->perf.initialized)
 		return;
 
+	unregister_sysctl_table(dev_priv->perf.sysctl_header);
+
 	i915_perf_deinit_sysfs_hsw(dev_priv);
 
 	kobject_put(dev_priv->perf.metrics_kobj);
-- 
2.7.1

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