drm/i915/gt: Discard stale context state from across idling

Before we idle, on parking, we switch to the kernel context such that we
have a scratch context loaded while the GPU idle, protecting any
precious user state. Be paranoid and assume that the idle state may have
been trashed, and reset the kernel_context image after idling.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Imre Deak <imre.deak@intel.com>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200102131707.1463945-4-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/gt/intel_engine_pm.c

@@ -20,6 +20,7 @@ static int __engine_unpark(struct intel_wakeref *wf)
 {
 	struct intel_engine_cs *engine =
 		container_of(wf, typeof(*engine), wakeref);
+	struct intel_context *ce;
 	void *map;
 
 	ENGINE_TRACE(engine, "\n");
@@ -34,6 +35,11 @@ static int __engine_unpark(struct intel_wakeref *wf)
 	if (!IS_ERR_OR_NULL(map))
 		engine->pinned_default_state = map;
 
+	/* Discard stale context state from across idling */
+	ce = engine->kernel_context;
+	if (ce)
+		ce->ops->reset(ce);
+
 	if (engine->unpark)
 		engine->unpark(engine);
 

drivers/gpu/drm/i915/gt/intel_gt_pm.c

@@ -213,16 +213,8 @@ int intel_gt_resume(struct intel_gt *gt)
 	intel_llc_enable(&gt->llc);
 
 	for_each_engine(engine, gt, id) {
-		struct intel_context *ce;
-
 		intel_engine_pm_get(engine);
 
-		ce = engine->kernel_context;
-		if (ce) {
-			GEM_BUG_ON(!intel_context_is_pinned(ce));
-			ce->ops->reset(ce);
-		}
-
 		engine->serial++; /* kernel context lost */
 		err = engine->resume(engine);
 

drivers/gpu/drm/i915/gt/mock_engine.c

@@ -152,6 +152,10 @@ static int mock_context_pin(struct intel_context *ce)
 	return intel_context_active_acquire(ce);
 }
 
+static void mock_context_reset(struct intel_context *ce)
+{
+}
+
 static const struct intel_context_ops mock_context_ops = {
 	.alloc = mock_context_alloc,
 
@@ -161,6 +165,7 @@ static const struct intel_context_ops mock_context_ops = {
 	.enter = intel_context_enter_engine,
 	.exit = intel_context_exit_engine,
 
+	.reset = mock_context_reset,
 	.destroy = mock_context_destroy,
 };