drm/i915: Allow overlapping userptr objects

Whilst I strongly advise against doing so for the implicit coherency
issues between the multiple buffer objects accessing the same backing
store, it nevertheless is a valid use case, akin to mmaping the same
file multiple times.

The reason why we forbade it earlier was that our use of the interval
tree for fast invalidation upon vma changes excluded overlapping
objects. So in the case where the user wishes to create such pairs of
overlapping objects, we degrade the range invalidation to walkin the
linear list of objects associated with the mm.

A situation where overlapping objects could arise is the lax implementation
of MIT-SHM Pixmaps in the xserver. A second situation is where the user
wishes to have different access modes to a region of memory (e.g. access
through a read-only userptr buffer and through a normal userptr buffer).

v2: Compile for mmu-notifiers after tweaking
v3: Rename is_linear/has_linear
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: "Li, Victor Y" <victor.y.li@intel.com>
Cc: "Kelley, Sean V" <sean.v.kelley@intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
Cc: "Gong, Zhipeng" <zhipeng.gong@intel.com>
Cc: Akash Goel <akash.goel@intel.com>
Cc: "Volkin, Bradley D" <bradley.d.volkin@intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_gem_userptr.c

@@ -40,19 +40,87 @@ struct i915_mmu_notifier {
 	struct hlist_node node;
 	struct mmu_notifier mn;
 	struct rb_root objects;
+	struct list_head linear;
 	struct drm_device *dev;
 	struct mm_struct *mm;
 	struct work_struct work;
 	unsigned long count;
 	unsigned long serial;
+	bool has_linear;
 };
 
 struct i915_mmu_object {
 	struct i915_mmu_notifier *mmu;
 	struct interval_tree_node it;
+	struct list_head link;
 	struct drm_i915_gem_object *obj;
+	bool is_linear;
 };
 
+static unsigned long cancel_userptr(struct drm_i915_gem_object *obj)
+{
+	struct drm_device *dev = obj->base.dev;
+	unsigned long end;
+
+	mutex_lock(&dev->struct_mutex);
+	/* Cancel any active worker and force us to re-evaluate gup */
+	obj->userptr.work = NULL;
+
+	if (obj->pages != NULL) {
+		struct drm_i915_private *dev_priv = to_i915(dev);
+		struct i915_vma *vma, *tmp;
+		bool was_interruptible;
+
+		was_interruptible = dev_priv->mm.interruptible;
+		dev_priv->mm.interruptible = false;
+
+		list_for_each_entry_safe(vma, tmp, &obj->vma_list, vma_link) {
+			int ret = i915_vma_unbind(vma);
+			WARN_ON(ret && ret != -EIO);
+		}
+		WARN_ON(i915_gem_object_put_pages(obj));
+
+		dev_priv->mm.interruptible = was_interruptible;
+	}
+
+	end = obj->userptr.ptr + obj->base.size;
+
+	drm_gem_object_unreference(&obj->base);
+	mutex_unlock(&dev->struct_mutex);
+
+	return end;
+}
+
+static void invalidate_range__linear(struct i915_mmu_notifier *mn,
+				     struct mm_struct *mm,
+				     unsigned long start,
+				     unsigned long end)
+{
+	struct i915_mmu_object *mmu;
+	unsigned long serial;
+
+restart:
+	serial = mn->serial;
+	list_for_each_entry(mmu, &mn->linear, link) {
+		struct drm_i915_gem_object *obj;
+
+		if (mmu->it.last < start || mmu->it.start > end)
+			continue;
+
+		obj = mmu->obj;
+		drm_gem_object_reference(&obj->base);
+		spin_unlock(&mn->lock);
+
+		cancel_userptr(obj);
+
+		spin_lock(&mn->lock);
+		if (serial != mn->serial)
+			goto restart;
+	}
+
+	spin_unlock(&mn->lock);
+}
+
 static void i915_gem_userptr_mn_invalidate_range_start(struct mmu_notifier *_mn,
 						       struct mm_struct *mm,
 						       unsigned long start,
@@ -60,16 +128,19 @@ static void i915_gem_userptr_mn_invalidate_range_start(struct mmu_notifier *_mn,
 {
 	struct i915_mmu_notifier *mn = container_of(_mn, struct i915_mmu_notifier, mn);
 	struct interval_tree_node *it = NULL;
+	unsigned long next = start;
 	unsigned long serial = 0;
 
 	end--; /* interval ranges are inclusive, but invalidate range is exclusive */
-	while (start < end) {
+	while (next < end) {
 		struct drm_i915_gem_object *obj;
 
 		obj = NULL;
 		spin_lock(&mn->lock);
+		if (mn->has_linear)
+			return invalidate_range__linear(mn, mm, start, end);
 		if (serial == mn->serial)
-			it = interval_tree_iter_next(it, start, end);
+			it = interval_tree_iter_next(it, next, end);
 		else
 			it = interval_tree_iter_first(&mn->objects, start, end);
 		if (it != NULL) {
@@ -81,31 +152,7 @@ static void i915_gem_userptr_mn_invalidate_range_start(struct mmu_notifier *_mn,
 		if (obj == NULL)
 			return;
 
-		mutex_lock(&mn->dev->struct_mutex);
-		/* Cancel any active worker and force us to re-evaluate gup */
-		obj->userptr.work = NULL;
-
-		if (obj->pages != NULL) {
-			struct drm_i915_private *dev_priv = to_i915(mn->dev);
-			struct i915_vma *vma, *tmp;
-			bool was_interruptible;
-
-			was_interruptible = dev_priv->mm.interruptible;
-			dev_priv->mm.interruptible = false;
-
-			list_for_each_entry_safe(vma, tmp, &obj->vma_list, vma_link) {
-				int ret = i915_vma_unbind(vma);
-				WARN_ON(ret && ret != -EIO);
-			}
-			WARN_ON(i915_gem_object_put_pages(obj));
-
-			dev_priv->mm.interruptible = was_interruptible;
-		}
-
-		start = obj->userptr.ptr + obj->base.size;
-
-		drm_gem_object_unreference(&obj->base);
-		mutex_unlock(&mn->dev->struct_mutex);
+		next = cancel_userptr(obj);
 	}
 }
 
@@ -151,6 +198,8 @@ i915_mmu_notifier_get(struct drm_device *dev, struct mm_struct *mm)
 	mmu->objects = RB_ROOT;
 	mmu->count = 0;
 	mmu->serial = 1;
+	INIT_LIST_HEAD(&mmu->linear);
+	mmu->has_linear = false;
 
 	/* Protected by mmap_sem (write-lock) */
 	ret = __mmu_notifier_register(&mmu->mn, mm);
@@ -197,6 +246,17 @@ static void __i915_mmu_notifier_update_serial(struct i915_mmu_notifier *mmu)
 		mmu->serial = 1;
 }
 
+static bool i915_mmu_notifier_has_linear(struct i915_mmu_notifier *mmu)
+{
+	struct i915_mmu_object *mn;
+
+	list_for_each_entry(mn, &mmu->linear, link)
+		if (mn->is_linear)
+			return true;
+
+	return false;
+}
+
 static void
 i915_mmu_notifier_del(struct i915_mmu_notifier *mmu,
 		      struct i915_mmu_object *mn)
@@ -204,6 +264,10 @@ i915_mmu_notifier_del(struct i915_mmu_notifier *mmu,
 	lockdep_assert_held(&mmu->dev->struct_mutex);
 
 	spin_lock(&mmu->lock);
+	list_del(&mn->link);
+	if (mn->is_linear)
+		mmu->has_linear = i915_mmu_notifier_has_linear(mmu);
+	else
 		interval_tree_remove(&mn->it, &mmu->objects);
 	__i915_mmu_notifier_update_serial(mmu);
 	spin_unlock(&mmu->lock);
@@ -230,7 +294,6 @@ i915_mmu_notifier_add(struct i915_mmu_notifier *mmu,
 	 */
 	i915_gem_retire_requests(mmu->dev);
 
-	/* Disallow overlapping userptr objects */
 	spin_lock(&mmu->lock);
 	it = interval_tree_iter_first(&mmu->objects,
 				      mn->it.start, mn->it.last);
@@ -243,14 +306,22 @@ i915_mmu_notifier_add(struct i915_mmu_notifier *mmu,
 		 * to flush their object references upon which the object will
 		 * be removed from the interval-tree, or the the range is
 		 * still in use by another client and the overlap is invalid.
+		 *
+		 * If we do have an overlap, we cannot use the interval tree
+		 * for fast range invalidation.
 		 */
 
 		obj = container_of(it, struct i915_mmu_object, it)->obj;
-		ret = obj->userptr.workers ? -EAGAIN : -EINVAL;
-	} else {
+		if (!obj->userptr.workers)
+			mmu->has_linear = mn->is_linear = true;
+		else
+			ret = -EAGAIN;
+	} else
 		interval_tree_insert(&mn->it, &mmu->objects);
+
+	if (ret == 0) {
+		list_add(&mn->link, &mmu->linear);
 		__i915_mmu_notifier_update_serial(mmu);
-		ret = 0;
 	}
 	spin_unlock(&mmu->lock);
 	mutex_unlock(&mmu->dev->struct_mutex);
@@ -611,12 +682,11 @@ static const struct drm_i915_gem_object_ops i915_gem_userptr_ops = {
  * We impose several restrictions upon the memory being mapped
  * into the GPU.
  * 1. It must be page aligned (both start/end addresses, i.e ptr and size).
- * 2. It cannot overlap any other userptr object in the same address space.
- * 3. It must be normal system memory, not a pointer into another map of IO
+ * 2. It must be normal system memory, not a pointer into another map of IO
  *    space (e.g. it must not be a GTT mmapping of another object).
- * 4. We only allow a bo as large as we could in theory map into the GTT,
+ * 3. We only allow a bo as large as we could in theory map into the GTT,
  *    that is we limit the size to the total size of the GTT.
- * 5. The bo is marked as being snoopable. The backing pages are left
+ * 4. The bo is marked as being snoopable. The backing pages are left
  *    accessible directly by the CPU, but reads and writes by the GPU may
  *    incur the cost of a snoop (unless you have an LLC architecture).
  *