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