drm/i915/selftests: Exercise adding requests to a full GGTT

A bug recently encountered involved the issue where are we were
submitting requests to different ppGTT, each would pin a segment of the
GGTT for its logical context and ring. However, this is invisible to
eviction as we do not tie the context/ring VMA to a request and so do
not automatically wait upon it them (instead they are marked as pinned,
preventing eviction entirely). Instead the eviction code must flush those
contexts by switching to the kernel context. This selftest tries to
fill the GGTT with contexts to exercise a path where the
switch-to-kernel-context failed to make forward progress and we fail
with ENOSPC.

v2: Make the hole in the filled GGTT explicit.
v3: Swap out the arbitrary timeout for a private notification from
i915_gem_evict_something()
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20171012125726.14736-3-chris@chris-wilson.co.ukReviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>

drivers/gpu/drm/i915/i915_gem_evict.c

@@ -33,6 +33,10 @@
 #include "intel_drv.h"
 #include "i915_trace.h"
 
+I915_SELFTEST_DECLARE(static struct igt_evict_ctl {
+	bool fail_if_busy:1;
+} igt_evict_ctl;)
+
 static bool ggtt_is_idle(struct drm_i915_private *i915)
 {
        struct intel_engine_cs *engine;
@@ -205,6 +209,9 @@ i915_gem_evict_something(struct i915_address_space *vm,
 	 * the kernel's there is no more we can evict.
 	 */
 	if (!ggtt_is_idle(dev_priv)) {
+		if (I915_SELFTEST_ONLY(igt_evict_ctl.fail_if_busy))
+			return -EBUSY;
+
 		ret = ggtt_flush(dev_priv);
 		if (ret)
 			return ret;

drivers/gpu/drm/i915/selftests/i915_gem_evict.c

@@ -24,6 +24,9 @@
 
 #include "../i915_selftest.h"
 
+#include "lib_sw_fence.h"
+#include "mock_context.h"
+#include "mock_drm.h"
 #include "mock_gem_device.h"
 
 static int populate_ggtt(struct drm_i915_private *i915)
@@ -325,6 +328,148 @@ static int igt_evict_vm(void *arg)
 	return err;
 }
 
+static int igt_evict_contexts(void *arg)
+{
+	const u64 PRETEND_GGTT_SIZE = 16ull << 20;
+	struct drm_i915_private *i915 = arg;
+	struct intel_engine_cs *engine;
+	enum intel_engine_id id;
+	struct reserved {
+		struct drm_mm_node node;
+		struct reserved *next;
+	} *reserved = NULL;
+	struct drm_mm_node hole;
+	unsigned long count;
+	int err;
+
+	/*
+	 * The purpose of this test is to verify that we will trigger an
+	 * eviction in the GGTT when constructing a request that requires
+	 * additional space in the GGTT for pinning the context. This space
+	 * is not directly tied to the request so reclaiming it requires
+	 * extra work.
+	 *
+	 * As such this test is only meaningful for full-ppgtt environments
+	 * where the GTT space of the request is separate from the GGTT
+	 * allocation required to build the request.
+	 */
+	if (!USES_FULL_PPGTT(i915))
+		return 0;
+
+	mutex_lock(&i915->drm.struct_mutex);
+
+	/* Reserve a block so that we know we have enough to fit a few rq */
+	memset(&hole, 0, sizeof(hole));
+	err = i915_gem_gtt_insert(&i915->ggtt.base, &hole,
+				  PRETEND_GGTT_SIZE, 0, I915_COLOR_UNEVICTABLE,
+				  0, i915->ggtt.base.total,
+				  PIN_NOEVICT);
+	if (err)
+		goto out_locked;
+
+	/* Make the GGTT appear small by filling it with unevictable nodes */
+	count = 0;
+	do {
+		struct reserved *r;
+
+		r = kcalloc(1, sizeof(*r), GFP_KERNEL);
+		if (!r) {
+			err = -ENOMEM;
+			goto out_locked;
+		}
+
+		if (i915_gem_gtt_insert(&i915->ggtt.base, &r->node,
+					1ul << 20, 0, I915_COLOR_UNEVICTABLE,
+					0, i915->ggtt.base.total,
+					PIN_NOEVICT)) {
+			kfree(r);
+			break;
+		}
+
+		r->next = reserved;
+		reserved = r;
+
+		count++;
+	} while (1);
+	drm_mm_remove_node(&hole);
+	mutex_unlock(&i915->drm.struct_mutex);
+	pr_info("Filled GGTT with %lu 1MiB nodes\n", count);
+
+	/* Overfill the GGTT with context objects and so try to evict one. */
+	for_each_engine(engine, i915, id) {
+		struct i915_sw_fence fence;
+		struct drm_file *file;
+
+		file = mock_file(i915);
+		if (IS_ERR(file))
+			return PTR_ERR(file);
+
+		count = 0;
+		mutex_lock(&i915->drm.struct_mutex);
+		onstack_fence_init(&fence);
+		do {
+			struct drm_i915_gem_request *rq;
+			struct i915_gem_context *ctx;
+
+			ctx = live_context(i915, file);
+			if (!ctx)
+				break;
+
+			/* We will need some GGTT space for the rq's context */
+			igt_evict_ctl.fail_if_busy = true;
+			rq = i915_gem_request_alloc(engine, ctx);
+			igt_evict_ctl.fail_if_busy = false;
+
+			if (IS_ERR(rq)) {
+				/* When full, fail_if_busy will trigger EBUSY */
+				if (PTR_ERR(rq) != -EBUSY) {
+					pr_err("Unexpected error from request alloc (ctx hw id %u, on %s): %d\n",
+					       ctx->hw_id, engine->name,
+					       (int)PTR_ERR(rq));
+					err = PTR_ERR(rq);
+				}
+				break;
+			}
+
+			/* Keep every request/ctx pinned until we are full */
+			err = i915_sw_fence_await_sw_fence_gfp(&rq->submit,
+							       &fence,
+							       GFP_KERNEL);
+			if (err < 0)
+				break;
+
+			i915_add_request(rq);
+			count++;
+			err = 0;
+		} while(1);
+		mutex_unlock(&i915->drm.struct_mutex);
+
+		onstack_fence_fini(&fence);
+		pr_info("Submitted %lu contexts/requests on %s\n",
+			count, engine->name);
+
+		mock_file_free(i915, file);
+		if (err)
+			break;
+	}
+
+	mutex_lock(&i915->drm.struct_mutex);
+out_locked:
+	while (reserved) {
+		struct reserved *next = reserved->next;
+
+		drm_mm_remove_node(&reserved->node);
+		kfree(reserved);
+
+		reserved = next;
+	}
+	if (drm_mm_node_allocated(&hole))
+		drm_mm_remove_node(&hole);
+	mutex_unlock(&i915->drm.struct_mutex);
+
+	return err;
+}
+
 int i915_gem_evict_mock_selftests(void)
 {
 	static const struct i915_subtest tests[] = {
@@ -348,3 +493,12 @@ int i915_gem_evict_mock_selftests(void)
 	drm_dev_unref(&i915->drm);
 	return err;
 }
+
+int i915_gem_evict_live_selftests(struct drm_i915_private *i915)
+{
+	static const struct i915_subtest tests[] = {
+		SUBTEST(igt_evict_contexts),
+	};
+
+	return i915_subtests(tests, i915);
+}

drivers/gpu/drm/i915/selftests/i915_live_selftests.h

@@ -15,6 +15,7 @@ selftest(objects, i915_gem_object_live_selftests)
 selftest(dmabuf, i915_gem_dmabuf_live_selftests)
 selftest(coherency, i915_gem_coherency_live_selftests)
 selftest(gtt, i915_gem_gtt_live_selftests)
+selftest(evict, i915_gem_evict_live_selftests)
 selftest(hugepages, i915_gem_huge_page_live_selftests)
 selftest(contexts, i915_gem_context_live_selftests)
 selftest(hangcheck, intel_hangcheck_live_selftests)

drivers/gpu/drm/i915/selftests/mock_context.c

@@ -73,11 +73,7 @@ mock_context(struct drm_i915_private *i915,
 
 void mock_context_close(struct i915_gem_context *ctx)
 {
-	i915_gem_context_set_closed(ctx);
-
-	i915_ppgtt_close(&ctx->ppgtt->base);
-
-	i915_gem_context_put(ctx);
+	context_close(ctx);
 }
 
 void mock_init_contexts(struct drm_i915_private *i915)