[PATCH v7 08/11] drm/i915: Add dev.i915.perf_stream_paranoid sysctl option

[Robert Bragg]

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 at sixbynine.org>
Reviewed-by: Matthew Auld <matthew.auld at intel.com>
---
 drivers/gpu/drm/i915/i915_drv.h  |  1 +
 drivers/gpu/drm/i915/i915_perf.c | 50 +++++++++++++++++++++++++++++++++++++++-
 2 files changed, 50 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index a968212..7010c6e 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -2166,6 +2166,7 @@ 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 aedefbc..ab4c171 100644
--- a/drivers/gpu/drm/i915/i915_perf.c
+++ b/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.
@@ -1174,7 +1179,13 @@ 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;
@@ -1418,6 +1429,39 @@ 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))
@@ -1448,6 +1492,8 @@ 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;
 }

@@ -1456,6 +1502,8 @@ 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;
 }
-- 
2.10.1