[Intel-gfx] [PATCH] drm/i915/gem: Store mmap_offsets in an rbtree rather than a plain list

[Chris Wilson <chris@chris-wilson.co.uk>]

Currently we create a new mmap_offset for every call to
mmap_offset_ioctl. This exposes ourselves to an abusive client that may
simply create new mmap_offsets ad infinitum, which will exhaust physical
memory and the virtual address space. In addition to the exhaustion, a
very long linear list of mmap_offsets causes other clients using the
object to incur long list walks -- these long lists can also be
generated by simply having many clients generate their own mmap_offset.

Switching to an rbtree store for obj->mmo.offsets allows us to use a
binary search for duplicated mmap_offsets (preventing the exhaustion
from a trivial malicious client), and also quickly search for matching
mmap_offsets on object close.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Abdiel Janulgue <abdiel.janulgue@linux.intel.com>
---
 drivers/gpu/drm/i915/gem/i915_gem_mman.c      | 93 +++++++++++++++++--
 drivers/gpu/drm/i915/gem/i915_gem_object.c    | 46 +++++++--
 .../gpu/drm/i915/gem/i915_gem_object_types.h  |  4 +-
 3 files changed, 124 insertions(+), 19 deletions(-)

diff --git a/drivers/gpu/drm/i915/gem/i915_gem_mman.c b/drivers/gpu/drm/i915/gem/i915_gem_mman.c
index b9fdac2f9003..2908a205faa9 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_mman.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_mman.c
@@ -455,10 +455,11 @@ static void i915_gem_object_release_mmap_gtt(struct drm_i915_gem_object *obj)
 
 void i915_gem_object_release_mmap_offset(struct drm_i915_gem_object *obj)
 {
-	struct i915_mmap_offset *mmo;
+	struct i915_mmap_offset *mmo, *mn;
 
 	spin_lock(&obj->mmo.lock);
-	list_for_each_entry(mmo, &obj->mmo.offsets, offset) {
+	rbtree_postorder_for_each_entry_safe(mmo, mn,
+					     &obj->mmo.offsets, offset) {
 		/*
 		 * vma_node_unmap for GTT mmaps handled already in
 		 * __i915_gem_object_release_mmap_gtt
@@ -487,6 +488,84 @@ void i915_gem_object_release_mmap(struct drm_i915_gem_object *obj)
 	i915_gem_object_release_mmap_offset(obj);
 }
 
+static struct i915_mmap_offset *
+lookup_mmo(struct drm_i915_gem_object *obj,
+	   enum i915_mmap_type mmap_type,
+	   struct drm_file *file)
+{
+	struct i915_mmap_offset *match = NULL;
+	struct rb_node *rb;
+
+	spin_lock(&obj->mmo.lock);
+	rb = obj->mmo.offsets.rb_node;
+	while (rb) {
+		struct i915_mmap_offset *mmo =
+			rb_entry(rb, typeof(*mmo), offset);
+
+		if (mmo->file < file) {
+			rb = rb->rb_right;
+			continue;
+		}
+
+		if (mmo->file > file) {
+			rb = rb->rb_left;
+			continue;
+		}
+
+		if (mmo->mmap_type < mmap_type) {
+			rb = rb->rb_right;
+			continue;
+		}
+
+		if (mmo->mmap_type > mmap_type) {
+			rb = rb->rb_left;
+			continue;
+		}
+
+		match = mmo;
+		break;
+	}
+	spin_unlock(&obj->mmo.lock);
+
+	return match;
+}
+
+static struct i915_mmap_offset *
+insert_mmo(struct drm_i915_gem_object *obj, struct i915_mmap_offset *mmo)
+{
+	struct rb_node *rb, **p;
+
+	spin_lock(&obj->mmo.lock);
+	rb = NULL;
+	p = &obj->mmo.offsets.rb_node;
+	while (*p) {
+		struct i915_mmap_offset *pos;
+
+		rb = *p;
+		pos = rb_entry(rb, typeof(*pos), offset);
+
+		if (pos->file < mmo->file) {
+			p = &rb->rb_right;
+			continue;
+		}
+
+		if (pos->file > mmo->file) {
+			p = &rb->rb_left;
+			continue;
+		}
+
+		if (pos->mmap_type < mmo->mmap_type)
+			p = &rb->rb_right;
+		else
+			p = &rb->rb_left;
+	}
+	rb_link_node(&mmo->offset, rb, p);
+	rb_insert_color(&mmo->offset, &obj->mmo.offsets);
+	spin_unlock(&obj->mmo.lock);
+
+	return mmo;
+}
+
 static struct i915_mmap_offset *
 mmap_offset_attach(struct drm_i915_gem_object *obj,
 		   enum i915_mmap_type mmap_type,
@@ -496,6 +575,10 @@ mmap_offset_attach(struct drm_i915_gem_object *obj,
 	struct i915_mmap_offset *mmo;
 	int err;
 
+	mmo = lookup_mmo(obj, mmap_type, file);
+	if (mmo)
+		return mmo;
+
 	mmo = kmalloc(sizeof(*mmo), GFP_KERNEL);
 	if (!mmo)
 		return ERR_PTR(-ENOMEM);
@@ -526,11 +609,7 @@ mmap_offset_attach(struct drm_i915_gem_object *obj,
 	if (file)
 		drm_vma_node_allow(&mmo->vma_node, file);
 
-	spin_lock(&obj->mmo.lock);
-	list_add(&mmo->offset, &obj->mmo.offsets);
-	spin_unlock(&obj->mmo.lock);
-
-	return mmo;
+	return insert_mmo(obj, mmo);
 
 err:
 	kfree(mmo);
diff --git a/drivers/gpu/drm/i915/gem/i915_gem_object.c b/drivers/gpu/drm/i915/gem/i915_gem_object.c
index 46bacc82ddc4..3cc9f83f0bae 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_object.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_object.c
@@ -63,7 +63,7 @@ void i915_gem_object_init(struct drm_i915_gem_object *obj,
 	INIT_LIST_HEAD(&obj->lut_list);
 
 	spin_lock_init(&obj->mmo.lock);
-	INIT_LIST_HEAD(&obj->mmo.offsets);
+	obj->mmo.offsets = RB_ROOT;
 
 	init_rcu_head(&obj->rcu);
 
@@ -96,6 +96,37 @@ void i915_gem_object_set_cache_coherency(struct drm_i915_gem_object *obj,
 		!(obj->cache_coherent & I915_BO_CACHE_COHERENT_FOR_WRITE);
 }
 
+static struct i915_mmap_offset *
+first_mmo(struct drm_i915_gem_object *obj, struct drm_file *file)
+{
+	struct i915_mmap_offset *first = NULL;
+	struct rb_node *pos;
+
+	pos = obj->mmo.offsets.rb_node;
+	while (pos) {
+		struct i915_mmap_offset *mmo =
+			rb_entry(pos, typeof(*mmo), offset);
+
+		if (mmo->file < file) {
+			pos = pos->rb_right;
+			continue;
+		}
+
+		pos = pos->rb_left;
+		if (mmo->file == file)
+			first = mmo;
+	}
+
+	return first;
+}
+
+static struct i915_mmap_offset *
+next_mmo(struct i915_mmap_offset *pos, struct drm_file *file)
+{
+	pos = rb_entry_safe(rb_next(&pos->offset), typeof(*pos), offset);
+	return pos && pos->file == file ? pos : NULL;
+}
+
 void i915_gem_close_object(struct drm_gem_object *gem, struct drm_file *file)
 {
 	struct drm_i915_gem_object *obj = to_intel_bo(gem);
@@ -117,14 +148,8 @@ void i915_gem_close_object(struct drm_gem_object *gem, struct drm_file *file)
 	i915_gem_object_unlock(obj);
 
 	spin_lock(&obj->mmo.lock);
-	list_for_each_entry(mmo, &obj->mmo.offsets, offset) {
-		if (mmo->file != file)
-			continue;
-
-		spin_unlock(&obj->mmo.lock);
+	for (mmo = first_mmo(obj, file); mmo; mmo = next_mmo(mmo, file))
 		drm_vma_node_revoke(&mmo->vma_node, file);
-		spin_lock(&obj->mmo.lock);
-	}
 	spin_unlock(&obj->mmo.lock);
 
 	list_for_each_entry_safe(lut, ln, &close, obj_link) {
@@ -203,12 +228,13 @@ static void __i915_gem_free_objects(struct drm_i915_private *i915,
 
 		i915_gem_object_release_mmap(obj);
 
-		list_for_each_entry_safe(mmo, mn, &obj->mmo.offsets, offset) {
+		rbtree_postorder_for_each_entry_safe(mmo, mn,
+						     &obj->mmo.offsets,
+						     offset) {
 			drm_vma_offset_remove(obj->base.dev->vma_offset_manager,
 					      &mmo->vma_node);
 			kfree(mmo);
 		}
-		INIT_LIST_HEAD(&obj->mmo.offsets);
 
 		GEM_BUG_ON(atomic_read(&obj->bind_count));
 		GEM_BUG_ON(obj->userfault_count);
diff --git a/drivers/gpu/drm/i915/gem/i915_gem_object_types.h b/drivers/gpu/drm/i915/gem/i915_gem_object_types.h
index 88e268633fdc..124fd2fb1bec 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_object_types.h
+++ b/drivers/gpu/drm/i915/gem/i915_gem_object_types.h
@@ -77,7 +77,7 @@ struct i915_mmap_offset {
 	struct drm_file *file;
 	enum i915_mmap_type mmap_type;
 
-	struct list_head offset;
+	struct rb_node offset;
 };
 
 struct drm_i915_gem_object {
@@ -137,7 +137,7 @@ struct drm_i915_gem_object {
 
 	struct {
 		spinlock_t lock; /* Protects access to mmo offsets */
-		struct list_head offsets;
+		struct rb_root offsets;
 	} mmo;
 
 	I915_SELFTEST_DECLARE(struct list_head st_link);
-- 
2.25.0

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