[PATCH] force-preempt-reset

[Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>]

A more concrete idea of what I think the serialisation should be between
reset timer and tasklet.

---
 drivers/gpu/drm/i915/intel_lrc.c        | 43 +++++++++++++++++++++++++++++++++
 drivers/gpu/drm/i915/intel_ringbuffer.h |  4 +++
 2 files changed, 47 insertions(+)

diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
index 2c2eb6d3868a..b6fd4323663d 100644
--- a/drivers/gpu/drm/i915/intel_lrc.c
+++ b/drivers/gpu/drm/i915/intel_lrc.c
@@ -531,6 +531,39 @@ static void inject_preempt_context(struct intel_engine_cs *engine)
 
 	execlists_clear_active(execlists, EXECLISTS_ACTIVE_HWACK);
 	execlists_set_active(execlists, EXECLISTS_ACTIVE_PREEMPT);
+
+	/* Set a timer to force preemption vs hostile userspace */
+	if (execlists->preempt_timeout_ns)
+		hrtimer_start(&execlists->preempt_timer,
+			      ktime_set(0, execlists->preempt_timeout_ns),
+			      HRTIMER_MODE_REL);
+}
+
+static enum hrtimer_restart preempt_timeout(struct hrtimer *hrtimer)
+{
+	struct intel_engine_cs *engine =
+		container_of(hrtimer, typeof(*engine), execlists.preempt_timer);
+
+	if (execlists_is_active(&engine->execlists, EXECLISTS_ACTIVE_PREEMPT))
+		queue_work(system_highpri_wq, &engine->execlists.preempt_reset);
+
+	return HRTIMER_NORESTART;
+}
+
+static void preempt_reset(struct work_struct *work)
+{
+	struct intel_engine_cs *engine =
+		container_of(work, typeof(*engine), execlists.preempt_reset);
+
+	tasklet_disable(&engine->execlists.tasklet);
+
+	engine->execlists.tasklet.func(engine->execlists.tasklet.data);
+
+	if (execlists_is_active(&engine->execlists, EXECLISTS_ACTIVE_PREEMPT))
+		i915_handle_error(engine->i915, BIT(engine->id), 0,
+				  "preemption timed out on %s", engine->name);
+
+	tasklet_enable(&engine->execlists.tasklet);
 }
 
 static void complete_preempt_context(struct intel_engine_execlists *execlists)
@@ -539,6 +572,11 @@ static void complete_preempt_context(struct intel_engine_execlists *execlists)
 	execlists_unwind_incomplete_requests(execlists);
 
 	GEM_BUG_ON(!execlists_is_active(execlists, EXECLISTS_ACTIVE_PREEMPT));
+
+	/* If the timer already fired, complete the reset */
+	if (hrtimer_try_to_cancel(&execlists->preempt_timer) < 0)
+		return;
+
 	execlists_clear_active(execlists, EXECLISTS_ACTIVE_PREEMPT);
 }
 
@@ -2182,6 +2220,11 @@ logical_ring_setup(struct intel_engine_cs *engine)
 	tasklet_init(&engine->execlists.tasklet,
 		     execlists_submission_tasklet, (unsigned long)engine);
 
+	INIT_WORK(&engine->execlists.preempt_reset, preempt_reset);
+	hrtimer_init(&engine->execlists.preempt_timer,
+		     CLOCK_MONOTONIC, HRTIMER_MODE_REL);
+	engine->execlists.preempt_timer.function = preempt_timeout;
+
 	logical_ring_default_vfuncs(engine);
 	logical_ring_default_irqs(engine);
 }
diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.h b/drivers/gpu/drm/i915/intel_ringbuffer.h
index 495b21fc33db..74fcff8a2a6e 100644
--- a/drivers/gpu/drm/i915/intel_ringbuffer.h
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.h
@@ -307,6 +307,10 @@ struct intel_engine_execlists {
 	 * @preempt_complete_status: expected CSB upon completing preemption
 	 */
 	u32 preempt_complete_status;
+
+	struct hrtimer preempt_timer;
+	struct work_struct preempt_reset;
+	unsigned long preempt_timeout_ns;
 };
 
 #define INTEL_ENGINE_CS_MAX_NAME 8
-- 
2.16.2

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