drm/i915/gem: Store mmap_offsets in an rbtree rather than a plain list

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.

However, we can simply use the drm_vma_node itself to manage the file
association (allow/revoke) dropping our need to keep an mmo per-file.
Then if we keep a small rbtree of per-type mmap_offsets, we can lookup
duplicate requests quickly.

Fixes: cc662126b413 ("drm/i915: Introduce DRM_I915_GEM_MMAP_OFFSET")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Abdiel Janulgue <abdiel.janulgue@linux.intel.com>
Reviewed-by: Abdiel Janulgue <abdiel.janulgue@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200120104924.4000706-3-chris@chris-wilson.co.uk

diff --git a/drivers/gpu/drm/i915/gem/i915_gem_mman.c b/drivers/gpu/drm/i915/gem/i915_gem_mman.c
index b9fdac2..e9be250 100644 (file)
--- a/drivers/gpu/drm/i915/gem/i915_gem_mman.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_mman.c
@@ -455,10 +455,11 @@ out:
 
 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
@@ -488,6 +489,67 @@ void i915_gem_object_release_mmap(struct drm_i915_gem_object *obj)
 }
 
 static struct i915_mmap_offset *
+lookup_mmo(struct drm_i915_gem_object *obj,
+          enum i915_mmap_type mmap_type)
+{
+       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->mmap_type == mmap_type) {
+                       spin_unlock(&obj->mmo.lock);
+                       return mmo;
+               }
+
+               if (mmo->mmap_type < mmap_type)
+                       rb = rb->rb_right;
+               else
+                       rb = rb->rb_left;
+       }
+       spin_unlock(&obj->mmo.lock);
+
+       return NULL;
+}
+
+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->mmap_type == mmo->mmap_type) {
+                       spin_unlock(&obj->mmo.lock);
+                       drm_vma_offset_remove(obj->base.dev->vma_offset_manager,
+                                             &mmo->vma_node);
+                       kfree(mmo);
+                       return pos;
+               }
+
+               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,
                   struct drm_file *file)
@@ -496,20 +558,22 @@ mmap_offset_attach(struct drm_i915_gem_object *obj,
        struct i915_mmap_offset *mmo;
        int err;
 
+       mmo = lookup_mmo(obj, mmap_type);
+       if (mmo)
+               goto out;
+
        mmo = kmalloc(sizeof(*mmo), GFP_KERNEL);
        if (!mmo)
                return ERR_PTR(-ENOMEM);
 
        mmo->obj = obj;
-       mmo->dev = obj->base.dev;
-       mmo->file = file;
        mmo->mmap_type = mmap_type;
        drm_vma_node_reset(&mmo->vma_node);
 
-       err = drm_vma_offset_add(mmo->dev->vma_offset_manager, &mmo->vma_node,
-                                obj->base.size / PAGE_SIZE);
+       err = drm_vma_offset_add(obj->base.dev->vma_offset_manager,
+                                &mmo->vma_node, obj->base.size / PAGE_SIZE);
        if (likely(!err))
-               goto out;
+               goto insert;
 
        /* Attempt to reap some mmap space from dead objects */
        err = intel_gt_retire_requests_timeout(&i915->gt, MAX_SCHEDULE_TIMEOUT);
@@ -517,19 +581,17 @@ mmap_offset_attach(struct drm_i915_gem_object *obj,
                goto err;
 
        i915_gem_drain_freed_objects(i915);
-       err = drm_vma_offset_add(mmo->dev->vma_offset_manager, &mmo->vma_node,
-                                obj->base.size / PAGE_SIZE);
+       err = drm_vma_offset_add(obj->base.dev->vma_offset_manager,
+                                &mmo->vma_node, obj->base.size / PAGE_SIZE);
        if (err)
                goto err;
 
+insert:
+       mmo = insert_mmo(obj, mmo);
+       GEM_BUG_ON(lookup_mmo(obj, mmap_type) != mmo);
 out:
        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;
 
 err:

diff --git a/drivers/gpu/drm/i915/gem/i915_gem_object.c b/drivers/gpu/drm/i915/gem/i915_gem_object.c
index 46bacc8..3598521 100644 (file)
--- 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);
 
@@ -100,8 +100,8 @@ void i915_gem_close_object(struct drm_gem_object *gem, struct drm_file *file)
 {
        struct drm_i915_gem_object *obj = to_intel_bo(gem);
        struct drm_i915_file_private *fpriv = file->driver_priv;
+       struct i915_mmap_offset *mmo, *mn;
        struct i915_lut_handle *lut, *ln;
-       struct i915_mmap_offset *mmo;
        LIST_HEAD(close);
 
        i915_gem_object_lock(obj);
@@ -117,14 +117,8 @@ 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);
+       rbtree_postorder_for_each_entry_safe(mmo, mn, &obj->mmo.offsets, offset)
                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 +197,14 @@ 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);
+               obj->mmo.offsets = RB_ROOT;
 
                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 88e2686..f64ad77 100644 (file)
--- a/drivers/gpu/drm/i915/gem/i915_gem_object_types.h
+++ b/drivers/gpu/drm/i915/gem/i915_gem_object_types.h
@@ -71,13 +71,11 @@ enum i915_mmap_type {
 };
 
 struct i915_mmap_offset {
-       struct drm_device *dev;
        struct drm_vma_offset_node vma_node;
        struct drm_i915_gem_object *obj;
-       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 +135,7 @@ 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);