drivers/gpu/drm/drm_vma_manager.c - kernel/msm-4.19 - Gitiles

 /*
  * Copyright (c) 2006-2009 VMware, Inc., Palo Alto, CA., USA
  * Copyright (c) 2012 David Airlie <airlied@linux.ie>
  * Copyright (c) 2013 David Herrmann <dh.herrmann@gmail.com>
  *
  * Permission is hereby granted, free of charge, to any person obtaining a
  * copy of this software and associated documentation files (the "Software"),
  * to deal in the Software without restriction, including without limitation
  * the rights to use, copy, modify, merge, publish, distribute, sublicense,
  * and/or sell copies of the Software, and to permit persons to whom the
  * Software is furnished to do so, subject to the following conditions:
  *
  * The above copyright notice and this permission notice shall be included in
  * all copies or substantial portions of the Software.
  *
  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
  * THE COPYRIGHT HOLDER(S) OR AUTHOR(S) BE LIABLE FOR ANY CLAIM, DAMAGES OR
  * OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
  * ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
  * OTHER DEALINGS IN THE SOFTWARE.
  */

 #include <drm/drmP.h>
 #include <drm/drm_mm.h>
 #include <drm/drm_vma_manager.h>
 #include <linux/mm.h>
 #include <linux/module.h>
 #include <linux/rbtree.h>
 #include <linux/slab.h>
 #include <linux/spinlock.h>
 #include <linux/types.h>

 /**
  * DOC: vma offset manager
  *
  * The vma-manager is responsible to map arbitrary driver-dependent memory
  * regions into the linear user address-space. It provides offsets to the
  * caller which can then be used on the address_space of the drm-device. It
  * takes care to not overlap regions, size them appropriately and to not
  * confuse mm-core by inconsistent fake vm_pgoff fields.
  * Drivers shouldn't use this for object placement in VMEM. This manager should
  * only be used to manage mappings into linear user-space VMs.
  *
  * We use drm_mm as backend to manage object allocations. But it is highly
  * optimized for alloc/free calls, not lookups. Hence, we use an rb-tree to
  * speed up offset lookups.
  *
  * You must not use multiple offset managers on a single address_space.
  * Otherwise, mm-core will be unable to tear down memory mappings as the VM will
  * no longer be linear.
  *
  * This offset manager works on page-based addresses. That is, every argument
  * and return code (with the exception of drm_vma_node_offset_addr()) is given
  * in number of pages, not number of bytes. That means, object sizes and offsets
  * must always be page-aligned (as usual).
  * If you want to get a valid byte-based user-space address for a given offset,
  * please see drm_vma_node_offset_addr().
  *
  * Additionally to offset management, the vma offset manager also handles access
  * management. For every open-file context that is allowed to access a given
  * node, you must call drm_vma_node_allow(). Otherwise, an mmap() call on this
  * open-file with the offset of the node will fail with -EACCES. To revoke
  * access again, use drm_vma_node_revoke(). However, the caller is responsible
  * for destroying already existing mappings, if required.
  */

 /**
  * drm_vma_offset_manager_init - Initialize new offset-manager
  * @mgr: Manager object
  * @page_offset: Offset of available memory area (page-based)
  * @size: Size of available address space range (page-based)
  *
  * Initialize a new offset-manager. The offset and area size available for the
  * manager are given as @page_offset and @size. Both are interpreted as
  * page-numbers, not bytes.
  *
  * Adding/removing nodes from the manager is locked internally and protected
  * against concurrent access. However, node allocation and destruction is left
  * for the caller. While calling into the vma-manager, a given node must
  * always be guaranteed to be referenced.
  */
 void drm_vma_offset_manager_init(struct drm_vma_offset_manager *mgr,
 				 unsigned long page_offset, unsigned long size)
 {
 	rwlock_init(&mgr->vm_lock);
 	drm_mm_init(&mgr->vm_addr_space_mm, page_offset, size);
 }
 EXPORT_SYMBOL(drm_vma_offset_manager_init);

 /**
  * drm_vma_offset_manager_destroy() - Destroy offset manager
  * @mgr: Manager object
  *
  * Destroy an object manager which was previously created via
  * drm_vma_offset_manager_init(). The caller must remove all allocated nodes
  * before destroying the manager. Otherwise, drm_mm will refuse to free the
  * requested resources.
  *
  * The manager must not be accessed after this function is called.
  */
 void drm_vma_offset_manager_destroy(struct drm_vma_offset_manager *mgr)
 {
 	/* take the lock to protect against buggy drivers */
 	write_lock(&mgr->vm_lock);
 	drm_mm_takedown(&mgr->vm_addr_space_mm);
 	write_unlock(&mgr->vm_lock);
 }
 EXPORT_SYMBOL(drm_vma_offset_manager_destroy);

 /**
  * drm_vma_offset_lookup_locked() - Find node in offset space
  * @mgr: Manager object
  * @start: Start address for object (page-based)
  * @pages: Size of object (page-based)
  *
  * Find a node given a start address and object size. This returns the _best_
  * match for the given node. That is, @start may point somewhere into a valid
  * region and the given node will be returned, as long as the node spans the
  * whole requested area (given the size in number of pages as @pages).
  *
  * Note that before lookup the vma offset manager lookup lock must be acquired
  * with drm_vma_offset_lock_lookup(). See there for an example. This can then be
  * used to implement weakly referenced lookups using kref_get_unless_zero().
  *
  * Example:
  *
  * ::
  *
  *     drm_vma_offset_lock_lookup(mgr);
  *     node = drm_vma_offset_lookup_locked(mgr);
  *     if (node)
  *         kref_get_unless_zero(container_of(node, sth, entr));
  *     drm_vma_offset_unlock_lookup(mgr);
  *
  * RETURNS:
  * Returns NULL if no suitable node can be found. Otherwise, the best match
  * is returned. It's the caller's responsibility to make sure the node doesn't
  * get destroyed before the caller can access it.
  */
 struct drm_vma_offset_node *drm_vma_offset_lookup_locked(struct drm_vma_offset_manager *mgr,
 							 unsigned long start,
 							 unsigned long pages)
 {
 	struct drm_mm_node *node, *best;
 	struct rb_node *iter;
 	unsigned long offset;

 	iter = mgr->vm_addr_space_mm.interval_tree.rb_node;
 	best = NULL;

 	while (likely(iter)) {
 		node = rb_entry(iter, struct drm_mm_node, rb);
 		offset = node->start;
 		if (start >= offset) {
 			iter = iter->rb_right;
 			best = node;
 			if (start == offset)
 				break;
 		} else {
 			iter = iter->rb_left;
 		}
 	}

 	/* verify that the node spans the requested area */
 	if (best) {
 		offset = best->start + best->size;
 		if (offset < start + pages)
 			best = NULL;
 	}

 	if (!best)
 		return NULL;

 	return container_of(best, struct drm_vma_offset_node, vm_node);
 }
 EXPORT_SYMBOL(drm_vma_offset_lookup_locked);

 /**
  * drm_vma_offset_add() - Add offset node to manager
  * @mgr: Manager object
  * @node: Node to be added
  * @pages: Allocation size visible to user-space (in number of pages)
  *
  * Add a node to the offset-manager. If the node was already added, this does
  * nothing and return 0. @pages is the size of the object given in number of
  * pages.
  * After this call succeeds, you can access the offset of the node until it
  * is removed again.
  *
  * If this call fails, it is safe to retry the operation or call
  * drm_vma_offset_remove(), anyway. However, no cleanup is required in that
  * case.
  *
  * @pages is not required to be the same size as the underlying memory object
  * that you want to map. It only limits the size that user-space can map into
  * their address space.
  *
  * RETURNS:
  * 0 on success, negative error code on failure.
  */
 int drm_vma_offset_add(struct drm_vma_offset_manager *mgr,
 		       struct drm_vma_offset_node *node, unsigned long pages)
 {
 	int ret;

 	write_lock(&mgr->vm_lock);

 	if (drm_mm_node_allocated(&node->vm_node)) {
 		ret = 0;
 		goto out_unlock;
 	}

 	ret = drm_mm_insert_node(&mgr->vm_addr_space_mm, &node->vm_node, pages);
 	if (ret)
 		goto out_unlock;

 out_unlock:
 	write_unlock(&mgr->vm_lock);
 	return ret;
 }
 EXPORT_SYMBOL(drm_vma_offset_add);

 /**
  * drm_vma_offset_remove() - Remove offset node from manager
  * @mgr: Manager object
  * @node: Node to be removed
  *
  * Remove a node from the offset manager. If the node wasn't added before, this
  * does nothing. After this call returns, the offset and size will be 0 until a
  * new offset is allocated via drm_vma_offset_add() again. Helper functions like
  * drm_vma_node_start() and drm_vma_node_offset_addr() will return 0 if no
  * offset is allocated.
  */
 void drm_vma_offset_remove(struct drm_vma_offset_manager *mgr,
 			   struct drm_vma_offset_node *node)
 {
 	write_lock(&mgr->vm_lock);

 	if (drm_mm_node_allocated(&node->vm_node)) {
 		drm_mm_remove_node(&node->vm_node);
 		memset(&node->vm_node, 0, sizeof(node->vm_node));
 	}

 	write_unlock(&mgr->vm_lock);
 }
 EXPORT_SYMBOL(drm_vma_offset_remove);

 /**
  * drm_vma_node_allow - Add open-file to list of allowed users
  * @node: Node to modify
  * @tag: Tag of file to remove
  *
  * Add @tag to the list of allowed open-files for this node. If @tag is
  * already on this list, the ref-count is incremented.
  *
  * The list of allowed-users is preserved across drm_vma_offset_add() and
  * drm_vma_offset_remove() calls. You may even call it if the node is currently
  * not added to any offset-manager.
  *
  * You must remove all open-files the same number of times as you added them
  * before destroying the node. Otherwise, you will leak memory.
  *
  * This is locked against concurrent access internally.
  *
  * RETURNS:
  * 0 on success, negative error code on internal failure (out-of-mem)
  */
 int drm_vma_node_allow(struct drm_vma_offset_node *node, struct drm_file *tag)
 {
 	struct rb_node **iter;
 	struct rb_node *parent = NULL;
 	struct drm_vma_offset_file *new, *entry;
 	int ret = 0;

 	/* Preallocate entry to avoid atomic allocations below. It is quite
 	 * unlikely that an open-file is added twice to a single node so we
 	 * don't optimize for this case. OOM is checked below only if the entry
 	 * is actually used. */
 	new = kmalloc(sizeof(*entry), GFP_KERNEL);

 	write_lock(&node->vm_lock);

 	iter = &node->vm_files.rb_node;

 	while (likely(*iter)) {
 		parent = *iter;
 		entry = rb_entry(*iter, struct drm_vma_offset_file, vm_rb);

 		if (tag == entry->vm_tag) {
 			entry->vm_count++;
 			goto unlock;
 		} else if (tag > entry->vm_tag) {
 			iter = &(*iter)->rb_right;
 		} else {
 			iter = &(*iter)->rb_left;
 		}
 	}

 	if (!new) {
 		ret = -ENOMEM;
 		goto unlock;
 	}

 	new->vm_tag = tag;
 	new->vm_count = 1;
 	rb_link_node(&new->vm_rb, parent, iter);
 	rb_insert_color(&new->vm_rb, &node->vm_files);
 	new = NULL;

 unlock:
 	write_unlock(&node->vm_lock);
 	kfree(new);
 	return ret;
 }
 EXPORT_SYMBOL(drm_vma_node_allow);

 /**
  * drm_vma_node_revoke - Remove open-file from list of allowed users
  * @node: Node to modify
  * @tag: Tag of file to remove
  *
  * Decrement the ref-count of @tag in the list of allowed open-files on @node.
  * If the ref-count drops to zero, remove @tag from the list. You must call
  * this once for every drm_vma_node_allow() on @tag.
  *
  * This is locked against concurrent access internally.
  *
  * If @tag is not on the list, nothing is done.
  */
 void drm_vma_node_revoke(struct drm_vma_offset_node *node,
 			 struct drm_file *tag)
 {
 	struct drm_vma_offset_file *entry;
 	struct rb_node *iter;

 	write_lock(&node->vm_lock);

 	iter = node->vm_files.rb_node;
 	while (likely(iter)) {
 		entry = rb_entry(iter, struct drm_vma_offset_file, vm_rb);
 		if (tag == entry->vm_tag) {
 			if (!--entry->vm_count) {
 				rb_erase(&entry->vm_rb, &node->vm_files);
 				kfree(entry);
 			}
 			break;
 		} else if (tag > entry->vm_tag) {
 			iter = iter->rb_right;
 		} else {
 			iter = iter->rb_left;
 		}
 	}

 	write_unlock(&node->vm_lock);
 }
 EXPORT_SYMBOL(drm_vma_node_revoke);

 /**
  * drm_vma_node_is_allowed - Check whether an open-file is granted access
  * @node: Node to check
  * @tag: Tag of file to remove
  *
  * Search the list in @node whether @tag is currently on the list of allowed
  * open-files (see drm_vma_node_allow()).
  *
  * This is locked against concurrent access internally.
  *
  * RETURNS:
  * true iff @filp is on the list
  */
 bool drm_vma_node_is_allowed(struct drm_vma_offset_node *node,
 			     struct drm_file *tag)
 {
 	struct drm_vma_offset_file *entry;
 	struct rb_node *iter;

 	read_lock(&node->vm_lock);

 	iter = node->vm_files.rb_node;
 	while (likely(iter)) {
 		entry = rb_entry(iter, struct drm_vma_offset_file, vm_rb);
 		if (tag == entry->vm_tag)
 			break;
 		else if (tag > entry->vm_tag)
 			iter = iter->rb_right;
 		else
 			iter = iter->rb_left;
 	}

 	read_unlock(&node->vm_lock);

 	return iter;
 }
 EXPORT_SYMBOL(drm_vma_node_is_allowed);
	/*
	* Copyright (c) 2006-2009 VMware, Inc., Palo Alto, CA., USA
	* Copyright (c) 2012 David Airlie <airlied@linux.ie>
	* Copyright (c) 2013 David Herrmann <dh.herrmann@gmail.com>
	*
	* Permission is hereby granted, free of charge, to any person obtaining a
	* copy of this software and associated documentation files (the "Software"),
	* to deal in the Software without restriction, including without limitation
	* the rights to use, copy, modify, merge, publish, distribute, sublicense,
	* and/or sell copies of the Software, and to permit persons to whom the
	* Software is furnished to do so, subject to the following conditions:
	*
	* The above copyright notice and this permission notice shall be included in
	* all copies or substantial portions of the Software.
	*
	* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
	* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
	* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
	* THE COPYRIGHT HOLDER(S) OR AUTHOR(S) BE LIABLE FOR ANY CLAIM, DAMAGES OR
	* OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
	* ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
	* OTHER DEALINGS IN THE SOFTWARE.
	*/

	#include <drm/drmP.h>
	#include <drm/drm_mm.h>
	#include <drm/drm_vma_manager.h>
	#include <linux/mm.h>
	#include <linux/module.h>
	#include <linux/rbtree.h>
	#include <linux/slab.h>
	#include <linux/spinlock.h>
	#include <linux/types.h>

	/**
	* DOC: vma offset manager
	*
	* The vma-manager is responsible to map arbitrary driver-dependent memory
	* regions into the linear user address-space. It provides offsets to the
	* caller which can then be used on the address_space of the drm-device. It
	* takes care to not overlap regions, size them appropriately and to not
	* confuse mm-core by inconsistent fake vm_pgoff fields.
	* Drivers shouldn't use this for object placement in VMEM. This manager should
	* only be used to manage mappings into linear user-space VMs.
	*
	* We use drm_mm as backend to manage object allocations. But it is highly
	* optimized for alloc/free calls, not lookups. Hence, we use an rb-tree to
	* speed up offset lookups.
	*
	* You must not use multiple offset managers on a single address_space.
	* Otherwise, mm-core will be unable to tear down memory mappings as the VM will
	* no longer be linear.
	*
	* This offset manager works on page-based addresses. That is, every argument
	* and return code (with the exception of drm_vma_node_offset_addr()) is given
	* in number of pages, not number of bytes. That means, object sizes and offsets
	* must always be page-aligned (as usual).
	* If you want to get a valid byte-based user-space address for a given offset,
	* please see drm_vma_node_offset_addr().
	*
	* Additionally to offset management, the vma offset manager also handles access
	* management. For every open-file context that is allowed to access a given
	* node, you must call drm_vma_node_allow(). Otherwise, an mmap() call on this
	* open-file with the offset of the node will fail with -EACCES. To revoke
	* access again, use drm_vma_node_revoke(). However, the caller is responsible
	* for destroying already existing mappings, if required.
	*/

	/**
	* drm_vma_offset_manager_init - Initialize new offset-manager
	* @mgr: Manager object
	* @page_offset: Offset of available memory area (page-based)
	* @size: Size of available address space range (page-based)
	*
	* Initialize a new offset-manager. The offset and area size available for the
	* manager are given as @page_offset and @size. Both are interpreted as
	* page-numbers, not bytes.
	*
	* Adding/removing nodes from the manager is locked internally and protected
	* against concurrent access. However, node allocation and destruction is left
	* for the caller. While calling into the vma-manager, a given node must
	* always be guaranteed to be referenced.
	*/
	void drm_vma_offset_manager_init(struct drm_vma_offset_manager *mgr,
	unsigned long page_offset, unsigned long size)
	{
	rwlock_init(&mgr->vm_lock);
	drm_mm_init(&mgr->vm_addr_space_mm, page_offset, size);
	}
	EXPORT_SYMBOL(drm_vma_offset_manager_init);

	/**
	* drm_vma_offset_manager_destroy() - Destroy offset manager
	* @mgr: Manager object
	*
	* Destroy an object manager which was previously created via
	* drm_vma_offset_manager_init(). The caller must remove all allocated nodes
	* before destroying the manager. Otherwise, drm_mm will refuse to free the
	* requested resources.
	*
	* The manager must not be accessed after this function is called.
	*/
	void drm_vma_offset_manager_destroy(struct drm_vma_offset_manager *mgr)
	{
	/* take the lock to protect against buggy drivers */
	write_lock(&mgr->vm_lock);
	drm_mm_takedown(&mgr->vm_addr_space_mm);
	write_unlock(&mgr->vm_lock);
	}
	EXPORT_SYMBOL(drm_vma_offset_manager_destroy);

	/**
	* drm_vma_offset_lookup_locked() - Find node in offset space
	* @mgr: Manager object
	* @start: Start address for object (page-based)
	* @pages: Size of object (page-based)
	*
	* Find a node given a start address and object size. This returns the _best_
	* match for the given node. That is, @start may point somewhere into a valid
	* region and the given node will be returned, as long as the node spans the
	* whole requested area (given the size in number of pages as @pages).
	*
	* Note that before lookup the vma offset manager lookup lock must be acquired
	* with drm_vma_offset_lock_lookup(). See there for an example. This can then be
	* used to implement weakly referenced lookups using kref_get_unless_zero().
	*
	* Example:
	*
	* ::
	*
	* drm_vma_offset_lock_lookup(mgr);
	* node = drm_vma_offset_lookup_locked(mgr);
	* if (node)
	* kref_get_unless_zero(container_of(node, sth, entr));
	* drm_vma_offset_unlock_lookup(mgr);
	*
	* RETURNS:
	* Returns NULL if no suitable node can be found. Otherwise, the best match
	* is returned. It's the caller's responsibility to make sure the node doesn't
	* get destroyed before the caller can access it.
	*/
	struct drm_vma_offset_node drm_vma_offset_lookup_locked(struct drm_vma_offset_manager mgr,
	unsigned long start,
	unsigned long pages)
	{
	struct drm_mm_node node, best;
	struct rb_node *iter;
	unsigned long offset;

	iter = mgr->vm_addr_space_mm.interval_tree.rb_node;
	best = NULL;

	while (likely(iter)) {
	node = rb_entry(iter, struct drm_mm_node, rb);
	offset = node->start;
	if (start >= offset) {
	iter = iter->rb_right;
	best = node;
	if (start == offset)
	break;
	} else {
	iter = iter->rb_left;
	}
	}

	/* verify that the node spans the requested area */
	if (best) {
	offset = best->start + best->size;
	if (offset < start + pages)
	best = NULL;
	}

	if (!best)
	return NULL;

	return container_of(best, struct drm_vma_offset_node, vm_node);
	}
	EXPORT_SYMBOL(drm_vma_offset_lookup_locked);

	/**
	* drm_vma_offset_add() - Add offset node to manager
	* @mgr: Manager object
	* @node: Node to be added
	* @pages: Allocation size visible to user-space (in number of pages)
	*
	* Add a node to the offset-manager. If the node was already added, this does
	* nothing and return 0. @pages is the size of the object given in number of
	* pages.
	* After this call succeeds, you can access the offset of the node until it
	* is removed again.
	*
	* If this call fails, it is safe to retry the operation or call
	* drm_vma_offset_remove(), anyway. However, no cleanup is required in that
	* case.
	*
	* @pages is not required to be the same size as the underlying memory object
	* that you want to map. It only limits the size that user-space can map into
	* their address space.
	*
	* RETURNS:
	* 0 on success, negative error code on failure.
	*/
	int drm_vma_offset_add(struct drm_vma_offset_manager *mgr,
	struct drm_vma_offset_node *node, unsigned long pages)
	{
	int ret;

	write_lock(&mgr->vm_lock);

	if (drm_mm_node_allocated(&node->vm_node)) {
	ret = 0;
	goto out_unlock;
	}

	ret = drm_mm_insert_node(&mgr->vm_addr_space_mm, &node->vm_node, pages);
	if (ret)
	goto out_unlock;

	out_unlock:
	write_unlock(&mgr->vm_lock);
	return ret;
	}
	EXPORT_SYMBOL(drm_vma_offset_add);

	/**
	* drm_vma_offset_remove() - Remove offset node from manager
	* @mgr: Manager object
	* @node: Node to be removed
	*
	* Remove a node from the offset manager. If the node wasn't added before, this
	* does nothing. After this call returns, the offset and size will be 0 until a
	* new offset is allocated via drm_vma_offset_add() again. Helper functions like
	* drm_vma_node_start() and drm_vma_node_offset_addr() will return 0 if no
	* offset is allocated.
	*/
	void drm_vma_offset_remove(struct drm_vma_offset_manager *mgr,
	struct drm_vma_offset_node *node)
	{
	write_lock(&mgr->vm_lock);

	if (drm_mm_node_allocated(&node->vm_node)) {
	drm_mm_remove_node(&node->vm_node);
	memset(&node->vm_node, 0, sizeof(node->vm_node));
	}

	write_unlock(&mgr->vm_lock);
	}
	EXPORT_SYMBOL(drm_vma_offset_remove);

	/**
	* drm_vma_node_allow - Add open-file to list of allowed users
	* @node: Node to modify
	* @tag: Tag of file to remove
	*
	* Add @tag to the list of allowed open-files for this node. If @tag is
	* already on this list, the ref-count is incremented.
	*
	* The list of allowed-users is preserved across drm_vma_offset_add() and
	* drm_vma_offset_remove() calls. You may even call it if the node is currently
	* not added to any offset-manager.
	*
	* You must remove all open-files the same number of times as you added them
	* before destroying the node. Otherwise, you will leak memory.
	*
	* This is locked against concurrent access internally.
	*
	* RETURNS:
	* 0 on success, negative error code on internal failure (out-of-mem)
	*/
	int drm_vma_node_allow(struct drm_vma_offset_node node, struct drm_file tag)
	{
	struct rb_node **iter;
	struct rb_node *parent = NULL;
	struct drm_vma_offset_file new, entry;
	int ret = 0;

	/* Preallocate entry to avoid atomic allocations below. It is quite
	* unlikely that an open-file is added twice to a single node so we
	* don't optimize for this case. OOM is checked below only if the entry
	* is actually used. */
	new = kmalloc(sizeof(*entry), GFP_KERNEL);

	write_lock(&node->vm_lock);

	iter = &node->vm_files.rb_node;

	while (likely(*iter)) {
	parent = *iter;
	entry = rb_entry(*iter, struct drm_vma_offset_file, vm_rb);

	if (tag == entry->vm_tag) {
	entry->vm_count++;
	goto unlock;
	} else if (tag > entry->vm_tag) {
	iter = &(*iter)->rb_right;
	} else {
	iter = &(*iter)->rb_left;
	}
	}

	if (!new) {
	ret = -ENOMEM;
	goto unlock;
	}

	new->vm_tag = tag;
	new->vm_count = 1;
	rb_link_node(&new->vm_rb, parent, iter);
	rb_insert_color(&new->vm_rb, &node->vm_files);
	new = NULL;

	unlock:
	write_unlock(&node->vm_lock);
	kfree(new);
	return ret;
	}
	EXPORT_SYMBOL(drm_vma_node_allow);

	/**
	* drm_vma_node_revoke - Remove open-file from list of allowed users
	* @node: Node to modify
	* @tag: Tag of file to remove
	*
	* Decrement the ref-count of @tag in the list of allowed open-files on @node.
	* If the ref-count drops to zero, remove @tag from the list. You must call
	* this once for every drm_vma_node_allow() on @tag.
	*
	* This is locked against concurrent access internally.
	*
	* If @tag is not on the list, nothing is done.
	*/
	void drm_vma_node_revoke(struct drm_vma_offset_node *node,
	struct drm_file *tag)
	{
	struct drm_vma_offset_file *entry;
	struct rb_node *iter;

	write_lock(&node->vm_lock);

	iter = node->vm_files.rb_node;
	while (likely(iter)) {
	entry = rb_entry(iter, struct drm_vma_offset_file, vm_rb);
	if (tag == entry->vm_tag) {
	if (!--entry->vm_count) {
	rb_erase(&entry->vm_rb, &node->vm_files);
	kfree(entry);
	}
	break;
	} else if (tag > entry->vm_tag) {
	iter = iter->rb_right;
	} else {
	iter = iter->rb_left;
	}
	}

	write_unlock(&node->vm_lock);
	}
	EXPORT_SYMBOL(drm_vma_node_revoke);

	/**
	* drm_vma_node_is_allowed - Check whether an open-file is granted access
	* @node: Node to check
	* @tag: Tag of file to remove
	*
	* Search the list in @node whether @tag is currently on the list of allowed
	* open-files (see drm_vma_node_allow()).
	*
	* This is locked against concurrent access internally.
	*
	* RETURNS:
	* true iff @filp is on the list
	*/
	bool drm_vma_node_is_allowed(struct drm_vma_offset_node *node,
	struct drm_file *tag)
	{
	struct drm_vma_offset_file *entry;
	struct rb_node *iter;

	read_lock(&node->vm_lock);

	iter = node->vm_files.rb_node;
	while (likely(iter)) {
	entry = rb_entry(iter, struct drm_vma_offset_file, vm_rb);
	if (tag == entry->vm_tag)
	break;
	else if (tag > entry->vm_tag)
	iter = iter->rb_right;
	else
	iter = iter->rb_left;
	}

	read_unlock(&node->vm_lock);

	return iter;
	}
	EXPORT_SYMBOL(drm_vma_node_is_allowed);