drm/i915/execlists: Cancel banned contexts on schedule-out

On schedule-out (CS completion) of a banned context, scrub the context
image so that we do not replay the active payload. The intent is that we
skip banned payloads on request submission so that the timeline
advancement continues on in the background. However, if we are returning
to a preempted request, i915_request_skip() is ineffective and instead we
need to patch up the context image so that it continues from the start
of the next request.

v2: Fixup cancellation so that we only scrub the payload of the active
request and do not short-circuit the breadcrumbs (which might cause
other contexts to execute out of order).
v3: Grammar pass

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191023133108.21401-3-chris@chris-wilson.co.uk

Author: ickle

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

@@ -234,6 +234,9 @@ static void execlists_init_reg_state(u32 *reg_state,
 				     const struct intel_engine_cs *engine,
 				     const struct intel_ring *ring,
 				     bool close);
+static void
+__execlists_update_reg_state(const struct intel_context *ce,
+			     const struct intel_engine_cs *engine);
 
 static void mark_eio(struct i915_request *rq)
 {
@@ -246,6 +249,31 @@ static void mark_eio(struct i915_request *rq)
 	i915_request_mark_complete(rq);
 }
 
+static struct i915_request *active_request(struct i915_request *rq)
+{
+	const struct intel_context * const ce = rq->hw_context;
+	struct i915_request *active = NULL;
+	struct list_head *list;
+
+	if (!i915_request_is_active(rq)) /* unwound, but incomplete! */
+		return rq;
+
+	rcu_read_lock();
+	list = &rcu_dereference(rq->timeline)->requests;
+	list_for_each_entry_from_reverse(rq, list, link) {
+		if (i915_request_completed(rq))
+			break;
+
+		if (rq->hw_context != ce)
+			break;
+
+		active = rq;
+	}
+	rcu_read_unlock();
+
+	return active;
+}
+
 static inline u32 intel_hws_preempt_address(struct intel_engine_cs *engine)
 {
 	return (i915_ggtt_offset(engine->status_page.vma) +
@@ -972,6 +1000,58 @@ static void kick_siblings(struct i915_request *rq, struct intel_context *ce)
 		tasklet_schedule(&ve->base.execlists.tasklet);
 }
 
+static void restore_default_state(struct intel_context *ce,
+				  struct intel_engine_cs *engine)
+{
+	u32 *regs = ce->lrc_reg_state;
+
+	if (engine->pinned_default_state)
+		memcpy(regs, /* skip restoring the vanilla PPHWSP */
+		       engine->pinned_default_state + LRC_STATE_PN * PAGE_SIZE,
+		       engine->context_size - PAGE_SIZE);
+
+	execlists_init_reg_state(regs, ce, engine, ce->ring, false);
+}
+
+static void reset_active(struct i915_request *rq,
+			 struct intel_engine_cs *engine)
+{
+	struct intel_context * const ce = rq->hw_context;
+
+	/*
+	 * The executing context has been cancelled. We want to prevent
+	 * further execution along this context and propagate the error on
+	 * to anything depending on its results.
+	 *
+	 * In __i915_request_submit(), we apply the -EIO and remove the
+	 * requests' payloads for any banned requests. But first, we must
+	 * rewind the context back to the start of the incomplete request so
+	 * that we do not jump back into the middle of the batch.
+	 *
+	 * We preserve the breadcrumbs and semaphores of the incomplete
+	 * requests so that inter-timeline dependencies (i.e other timelines)
+	 * remain correctly ordered. And we defer to __i915_request_submit()
+	 * so that all asynchronous waits are correctly handled.
+	 */
+	GEM_TRACE("%s(%s): { rq=%llx:%lld }\n",
+		  __func__, engine->name, rq->fence.context, rq->fence.seqno);
+
+	/* On resubmission of the active request, payload will be scrubbed */
+	rq = active_request(rq);
+	if (rq)
+		ce->ring->head = intel_ring_wrap(ce->ring, rq->head);
+	else
+		ce->ring->head = ce->ring->tail;
+	intel_ring_update_space(ce->ring);
+
+	/* Scrub the context image to prevent replaying the previous batch */
+	restore_default_state(ce, engine);
+	__execlists_update_reg_state(ce, engine);
+
+	/* We've switched away, so this should be a no-op, but intent matters */
+	ce->lrc_desc |= CTX_DESC_FORCE_RESTORE;
+}
+
 static inline void
 __execlists_schedule_out(struct i915_request *rq,
 			 struct intel_engine_cs * const engine)
@@ -982,6 +1062,9 @@ __execlists_schedule_out(struct i915_request *rq,
 	execlists_context_status_change(rq, INTEL_CONTEXT_SCHEDULE_OUT);
 	intel_gt_pm_put(engine->gt);
 
+	if (unlikely(i915_gem_context_is_banned(ce->gem_context)))
+		reset_active(rq, engine);
+
 	/*
 	 * If this is part of a virtual engine, its next request may
 	 * have been blocked waiting for access to the active context.
@@ -1380,6 +1463,10 @@ static unsigned long active_preempt_timeout(struct intel_engine_cs *engine)
 	if (!rq)
 		return 0;
 
+	/* Force a fast reset for terminated contexts (ignoring sysfs!) */
+	if (unlikely(i915_gem_context_is_banned(rq->gem_context)))
+		return 1;
+
 	return READ_ONCE(engine->props.preempt_timeout_ms);
 }
 
@@ -2792,29 +2879,6 @@ static void reset_csb_pointers(struct intel_engine_cs *engine)
 			       &execlists->csb_status[reset_value]);
 }
 
-static struct i915_request *active_request(struct i915_request *rq)
-{
-	const struct intel_context * const ce = rq->hw_context;
-	struct i915_request *active = NULL;
-	struct list_head *list;
-
-	if (!i915_request_is_active(rq)) /* unwound, but incomplete! */
-		return rq;
-
-	list = &i915_request_active_timeline(rq)->requests;
-	list_for_each_entry_from_reverse(rq, list, link) {
-		if (i915_request_completed(rq))
-			break;
-
-		if (rq->hw_context != ce)
-			break;
-
-		active = rq;
-	}
-
-	return active;
-}
-
 static void __execlists_reset_reg_state(const struct intel_context *ce,
 					const struct intel_engine_cs *engine)
 {
@@ -2831,7 +2895,6 @@ static void __execlists_reset(struct intel_engine_cs *engine, bool stalled)
 	struct intel_engine_execlists * const execlists = &engine->execlists;
 	struct intel_context *ce;
 	struct i915_request *rq;
-	u32 *regs;
 
 	mb(); /* paranoia: read the CSB pointers from after the reset */
 	clflush(execlists->csb_write);
@@ -2907,13 +2970,7 @@ static void __execlists_reset(struct intel_engine_cs *engine, bool stalled)
 	 * to recreate its own state.
 	 */
 	GEM_BUG_ON(!intel_context_is_pinned(ce));
-	regs = ce->lrc_reg_state;
-	if (engine->pinned_default_state) {
-		memcpy(regs, /* skip restoring the vanilla PPHWSP */
-		       engine->pinned_default_state + LRC_STATE_PN * PAGE_SIZE,
-		       engine->context_size - PAGE_SIZE);
-	}
-	execlists_init_reg_state(regs, ce, engine, ce->ring, false);
+	restore_default_state(ce, engine);
 
 out_replay:
 	GEM_TRACE("%s replay {head:%04x, tail:%04x\n",
@@ -4574,16 +4631,8 @@ void intel_lr_context_reset(struct intel_engine_cs *engine,
 	 * future request will be after userspace has had the opportunity
 	 * to recreate its own state.
 	 */
-	if (scrub) {
-		u32 *regs = ce->lrc_reg_state;
-
-		if (engine->pinned_default_state) {
-			memcpy(regs, /* skip restoring the vanilla PPHWSP */
-			       engine->pinned_default_state + LRC_STATE_PN * PAGE_SIZE,
-			       engine->context_size - PAGE_SIZE);
-		}
-		execlists_init_reg_state(regs, ce, engine, ce->ring, false);
-	}
+	if (scrub)
+		restore_default_state(ce, engine);
 
 	/* Rerun the request; its payload has been neutered (if guilty). */
 	ce->ring->head = head;