dev/drm/drm_gem.c

/*
 * Copyright © 2008 Intel Corporation
 *
 * 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 (including the next
 * paragraph) 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 AUTHORS OR COPYRIGHT HOLDERS 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.
 *
 * Authors:
 *    Eric Anholt <eric@anholt.net>
 *
 */
/*-
 * Copyright (c) 2011 The FreeBSD Foundation
 * All rights reserved.
 *
 * This software was developed by Konstantin Belousov under sponsorship from
 * the FreeBSD Foundation.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

#include "opt_vm.h"

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/limits.h>
#include <sys/lock.h>
#include <sys/mutex.h>
#include <sys/conf.h>

#include <vm/vm.h>
#include <vm/vm_page.h>

#include <linux/types.h>
#include <linux/mm.h>
#include <linux/module.h>
#include <drm/drmP.h>
#include <drm/drm_vma_manager.h>
#include <drm/drm_gem.h>
#include "drm_internal.h"

/** @file drm_gem.c
 *
 * This file provides some of the base ioctls and library routines for
 * the graphics memory manager implemented by each device driver.
 *
 * Because various devices have different requirements in terms of
 * synchronization and migration strategies, implementing that is left up to
 * the driver, and all that the general API provides should be generic --
 * allocating objects, reading/writing data with the cpu, freeing objects.
 * Even there, platform-dependent optimizations for reading/writing data with
 * the CPU mean we'll likely hook those out to driver-specific calls.  However,
 * the DRI2 implementation wants to have at least allocate/mmap be generic.
 *
 * The goal was to have swap-backed object allocation managed through
 * struct file.  However, file descriptors as handles to a struct file have
 * two major failings:
 * - Process limits prevent more than 1024 or so being used at a time by
 *   default.
 * - Inability to allocate high fds will aggravate the X Server's select()
 *   handling, and likely that of many GL client applications as well.
 *
 * This led to a plan of using our own integer IDs (called handles, following
 * DRM terminology) to mimic fds, and implement the fd syscalls we need as
 * ioctls.  The objects themselves will still include the struct file so
 * that we can transition to fds if the required kernel infrastructure shows
 * up at a later date, and as our interface with shmfs for memory allocation.
 */

/*
 * We make up offsets for buffer objects so we can recognize them at
 * mmap time.
 */

/* pgoff in mmap is an unsigned long, so we need to make sure that
 * the faked up offset will fit
 */

#if BITS_PER_LONG == 64
#define DRM_FILE_PAGE_OFFSET_START ((0xFFFFFFFFUL >> PAGE_SHIFT) + 1)
#define DRM_FILE_PAGE_OFFSET_SIZE ((0xFFFFFFFFUL >> PAGE_SHIFT) * 16)
#else
#define DRM_FILE_PAGE_OFFSET_START ((0xFFFFFFFUL >> PAGE_SHIFT) + 1)
#define DRM_FILE_PAGE_OFFSET_SIZE ((0xFFFFFFFUL >> PAGE_SHIFT) * 16)
#endif

/**
 * drm_gem_init - Initialize the GEM device fields
 * @dev: drm_devic structure to initialize
 */
int
drm_gem_init(struct drm_device *dev)
{
	struct drm_gem_mm *mm;

	lockinit(&dev->object_name_lock, "objnam", 0, LK_CANRECURSE);
	idr_init(&dev->object_name_idr);

	mm = kzalloc(sizeof(struct drm_gem_mm), GFP_KERNEL);
	if (!mm) {
		DRM_ERROR("out of memory\n");
		return -ENOMEM;
	}

	dev->mm_private = mm;

	if (drm_ht_create(&mm->offset_hash, 12)) {
		kfree(mm);
		return -ENOMEM;
	}

	mm->idxunr = new_unrhdr(0, DRM_GEM_MAX_IDX, NULL);
	drm_mm_init(&mm->offset_manager, DRM_FILE_PAGE_OFFSET_START,
		    DRM_FILE_PAGE_OFFSET_SIZE);
	drm_vma_offset_manager_init(&mm->vma_manager,
				    DRM_FILE_PAGE_OFFSET_START,
				    DRM_FILE_PAGE_OFFSET_SIZE);

	return 0;
}

void
drm_gem_destroy(struct drm_device *dev)
{
	struct drm_gem_mm *mm = dev->mm_private;

	drm_mm_takedown(&mm->offset_manager);
	drm_ht_remove(&mm->offset_hash);

	drm_vma_offset_manager_destroy(&mm->vma_manager);
	delete_unrhdr(mm->idxunr);
	kfree(mm);
	dev->mm_private = NULL;
}

/**
 * Initialize an already allocated GEM object of the specified size with
 * shmfs backing store.
 */
int drm_gem_object_init(struct drm_device *dev,
			struct drm_gem_object *obj, size_t size)
{
	drm_gem_private_object_init(dev, obj, size);

	obj->vm_obj = default_pager_alloc(NULL, size,
	    VM_PROT_READ | VM_PROT_WRITE, 0);

	return 0;
}
EXPORT_SYMBOL(drm_gem_object_init);

/**
 * drm_gem_object_init - initialize an allocated private GEM object
 * @dev: drm_device the object should be initialized for
 * @obj: drm_gem_object to initialize
 * @size: object size
 *
 * Initialize an already allocated GEM object of the specified size with
 * no GEM provided backing store. Instead the caller is responsible for
 * backing the object and handling it.
 */
void drm_gem_private_object_init(struct drm_device *dev,
				 struct drm_gem_object *obj, size_t size)
{
	BUG_ON((size & (PAGE_SIZE - 1)) != 0);

	obj->dev = dev;
	obj->vm_obj = NULL;

	kref_init(&obj->refcount);
	obj->handle_count = 0;
	obj->size = size;
	drm_vma_node_reset(&obj->vma_node);
}
EXPORT_SYMBOL(drm_gem_private_object_init);

static void
drm_gem_remove_prime_handles(struct drm_gem_object *obj, struct drm_file *filp)
{
#if 0
	if (obj->import_attach) {
		drm_prime_remove_buf_handle(&filp->prime,
				obj->import_attach->dmabuf);
	}
	if (obj->export_dma_buf) {
		drm_prime_remove_buf_handle(&filp->prime,
				obj->export_dma_buf);
	}
#endif
}

static void drm_gem_object_ref_bug(struct kref *list_kref)
{
	BUG();
}

/**
 * drm_gem_object_free - release resources bound to userspace handles
 * @obj: GEM object to clean up.
 *
 * Called after the last handle to the object has been closed
 *
 * Removes any name for the object. Note that this must be
 * called before drm_gem_object_free or we'll be touching
 * freed memory
 */
static void drm_gem_object_handle_free(struct drm_gem_object *obj)
{
	struct drm_device *dev = obj->dev;

	/* Remove any name for this object */
	if (obj->name) {
		idr_remove(&dev->object_name_idr, obj->name);
		obj->name = 0;
	/*
	 * The object name held a reference to this object, drop
	 * that now.
	*
	* This cannot be the last reference, since the handle holds one too.
	 */
		kref_put(&obj->refcount, drm_gem_object_ref_bug);
	}
}

#if 0
static void drm_gem_object_exported_dma_buf_free(struct drm_gem_object *obj)
{
	/* Unbreak the reference cycle if we have an exported dma_buf. */
	if (obj->dma_buf) {
		dma_buf_put(obj->dma_buf);
		obj->dma_buf = NULL;
	}
}
#endif

static void
drm_gem_object_handle_unreference_unlocked(struct drm_gem_object *obj)
{
	if (WARN_ON(obj->handle_count == 0))
		return;

	/*
	* Must bump handle count first as this may be the last
	* ref, in which case the object would disappear before we
	* checked for a name
	*/

	mutex_lock(&obj->dev->object_name_lock);
	if (--obj->handle_count == 0)
		drm_gem_object_handle_free(obj);
	mutex_unlock(&obj->dev->object_name_lock);

	drm_gem_object_unreference_unlocked(obj);
}

/**
 * drm_gem_handle_delete - deletes the given file-private handle
 * @filp: drm file-private structure to use for the handle look up
 * @handle: userspace handle to delete
 *
 * Removes the GEM handle from the @filp lookup table and if this is the last
 * handle also cleans up linked resources like GEM names.
 */
int
drm_gem_handle_delete(struct drm_file *filp, u32 handle)
{
	struct drm_device *dev;
	struct drm_gem_object *obj;

	/* This is gross. The idr system doesn't let us try a delete and
	 * return an error code.  It just spews if you fail at deleting.
	 * So, we have to grab a lock around finding the object and then
	 * doing the delete on it and dropping the refcount, or the user
	 * could race us to double-decrement the refcount and cause a
	 * use-after-free later.  Given the frequency of our handle lookups,
	 * we may want to use ida for number allocation and a hash table
	 * for the pointers, anyway.
	 */
	lockmgr(&filp->table_lock, LK_EXCLUSIVE);

	/* Check if we currently have a reference on the object */
	obj = idr_find(&filp->object_idr, handle);
	if (obj == NULL) {
		lockmgr(&filp->table_lock, LK_RELEASE);
		return -EINVAL;
	}
	dev = obj->dev;

	/* Release reference and decrement refcount. */
	idr_remove(&filp->object_idr, handle);
	lockmgr(&filp->table_lock, LK_RELEASE);

	drm_gem_remove_prime_handles(obj, filp);

	if (dev->driver->gem_close_object)
		dev->driver->gem_close_object(obj, filp);
	drm_gem_object_handle_unreference_unlocked(obj);

	return 0;
}
EXPORT_SYMBOL(drm_gem_handle_delete);

/**
 * drm_gem_dumb_destroy - dumb fb callback helper for gem based drivers
 * @file: drm file-private structure to remove the dumb handle from
 * @dev: corresponding drm_device
 * @handle: the dumb handle to remove
 *
 * This implements the ->dumb_destroy kms driver callback for drivers which use
 * gem to manage their backing storage.
 */
int drm_gem_dumb_destroy(struct drm_file *file,
			 struct drm_device *dev,
			 uint32_t handle)
{
	return drm_gem_handle_delete(file, handle);
}
EXPORT_SYMBOL(drm_gem_dumb_destroy);

/**
 * drm_gem_handle_create_tail - internal functions to create a handle
 * @file_priv: drm file-private structure to register the handle for
 * @obj: object to register
 * @handlep: pointer to return the created handle to the caller
 *
 * This expects the dev->object_name_lock to be held already and will drop it
 * before returning. Used to avoid races in establishing new handles when
 * importing an object from either an flink name or a dma-buf.
 */
int
drm_gem_handle_create_tail(struct drm_file *file_priv,
			   struct drm_gem_object *obj,
			   u32 *handlep)
{
	struct drm_device *dev = obj->dev;
	int ret;

	*handlep = 0;		/* whack gcc warning */
	WARN_ON(!mutex_is_locked(&dev->object_name_lock));

	/*
	 * Get the user-visible handle using idr.  Preload and perform
	 * allocation under our spinlock.
	 */
	idr_preload(GFP_KERNEL);
	lockmgr(&file_priv->table_lock, LK_EXCLUSIVE);

	ret = idr_alloc(&file_priv->object_idr, obj, 1, 0, GFP_NOWAIT);
	drm_gem_object_reference(obj);
	obj->handle_count++;
	lockmgr(&file_priv->table_lock, LK_RELEASE);
	idr_preload_end();
	mutex_unlock(&dev->object_name_lock);
	if (ret < 0) {
		drm_gem_object_handle_unreference_unlocked(obj);
		return ret;
	}
	*handlep = ret;

#if 0
	ret = drm_vma_node_allow(&obj->vma_node, file_priv->filp);
	if (ret) {
		drm_gem_handle_delete(file_priv, *handlep);
		return ret;
	}
#endif

	if (dev->driver->gem_open_object) {
		ret = dev->driver->gem_open_object(obj, file_priv);
		if (ret) {
			drm_gem_handle_delete(file_priv, *handlep);
			return ret;
		}
	}

	return 0;
}

/**
 * drm_gem_handle_create - create a gem handle for an object
 * @file_priv: drm file-private structure to register the handle for
 * @obj: object to register
 * @handlep: pionter to return the created handle to the caller
 *
 * Create a handle for this object. This adds a handle reference
 * to the object, which includes a regular reference count. Callers
 * will likely want to dereference the object afterwards.
 */
int drm_gem_handle_create(struct drm_file *file_priv,
			  struct drm_gem_object *obj,
			  u32 *handlep)
{
	mutex_lock(&obj->dev->object_name_lock);

	return drm_gem_handle_create_tail(file_priv, obj, handlep);
}
EXPORT_SYMBOL(drm_gem_handle_create);

/**
 * drm_gem_free_mmap_offset - release a fake mmap offset for an object
 * @obj: obj in question
 *
 * This routine frees fake offsets allocated by drm_gem_create_mmap_offset().
 */
void
drm_gem_free_mmap_offset(struct drm_gem_object *obj)
{
	struct drm_device *dev = obj->dev;
	struct drm_gem_mm *mm = dev->mm_private;
	struct drm_hash_item *list;

	if (!obj->on_map)
		return;
	list = &obj->map_list;

	drm_ht_remove_item(&mm->offset_hash, list);
	free_unr(mm->idxunr, list->key);
	obj->on_map = false;

	drm_vma_offset_remove(&mm->vma_manager, &obj->vma_node);
}
EXPORT_SYMBOL(drm_gem_free_mmap_offset);

/**
 * drm_gem_create_mmap_offset_size - create a fake mmap offset for an object
 * @obj: obj in question
 * @size: the virtual size
 *
 * GEM memory mapping works by handing back to userspace a fake mmap offset
 * it can use in a subsequent mmap(2) call.  The DRM core code then looks
 * up the object based on the offset and sets up the various memory mapping
 * structures.
 *
 * This routine allocates and attaches a fake offset for @obj, in cases where
 * the virtual size differs from the physical size (ie. obj->size).  Otherwise
 * just use drm_gem_create_mmap_offset().
 */
int
drm_gem_create_mmap_offset_size(struct drm_gem_object *obj, size_t size)
{
	struct drm_device *dev = obj->dev;
	struct drm_gem_mm *mm = dev->mm_private;
	int ret = 0;

	if (obj->on_map)
		return (0);

	obj->map_list.key = alloc_unr(mm->idxunr);
	ret = drm_ht_insert_item(&mm->offset_hash, &obj->map_list);
	if (ret != 0) {
		DRM_ERROR("failed to add to map hash\n");
		free_unr(mm->idxunr, obj->map_list.key);
		return (ret);
	}
	obj->on_map = true;
	return 0;

	return drm_vma_offset_add(&mm->vma_manager, &obj->vma_node,
				  size / PAGE_SIZE);
}
EXPORT_SYMBOL(drm_gem_create_mmap_offset_size);

/**
 * drm_gem_create_mmap_offset - create a fake mmap offset for an object
 * @obj: obj in question
 *
 * GEM memory mapping works by handing back to userspace a fake mmap offset
 * it can use in a subsequent mmap(2) call.  The DRM core code then looks
 * up the object based on the offset and sets up the various memory mapping
 * structures.
 *
 * This routine allocates and attaches a fake offset for @obj.
 */
int drm_gem_create_mmap_offset(struct drm_gem_object *obj)
{
	return drm_gem_create_mmap_offset_size(obj, obj->size);
}
EXPORT_SYMBOL(drm_gem_create_mmap_offset);

/** Returns a reference to the object named by the handle. */
struct drm_gem_object *
drm_gem_object_lookup(struct drm_device *dev, struct drm_file *filp,
		      u32 handle)
{
	struct drm_gem_object *obj;

	lockmgr(&filp->table_lock, LK_EXCLUSIVE);

	/* Check if we currently have a reference on the object */
	obj = idr_find(&filp->object_idr, handle);
	if (obj == NULL) {
		lockmgr(&filp->table_lock, LK_RELEASE);
		return NULL;
	}

	drm_gem_object_reference(obj);

	lockmgr(&filp->table_lock, LK_RELEASE);

	return obj;
}
EXPORT_SYMBOL(drm_gem_object_lookup);

/**
 * drm_gem_close_ioctl - implementation of the GEM_CLOSE ioctl
 * @dev: drm_device
 * @data: ioctl data
 * @file_priv: drm file-private structure
 *
 * Releases the handle to an mm object.
 */
int
drm_gem_close_ioctl(struct drm_device *dev, void *data,
		    struct drm_file *file_priv)
{
	struct drm_gem_close *args = data;
	int ret;

	if (!drm_core_check_feature(dev, DRIVER_GEM))
		return -ENODEV;

	ret = drm_gem_handle_delete(file_priv, args->handle);

	return ret;
}

/**
 * Create a global name for an object, returning the name.
 *
 * Note that the name does not hold a reference; when the object
 * is freed, the name goes away.
 */
int
drm_gem_flink_ioctl(struct drm_device *dev, void *data,
		    struct drm_file *file_priv)
{
	struct drm_gem_flink *args = data;
	struct drm_gem_object *obj;
	int ret;

	if (!drm_core_check_feature(dev, DRIVER_GEM))
		return -ENODEV;

	obj = drm_gem_object_lookup(dev, file_priv, args->handle);
	if (obj == NULL)
		return -ENOENT;

	idr_preload(GFP_KERNEL);
	lockmgr(&dev->object_name_lock, LK_EXCLUSIVE);
	/* prevent races with concurrent gem_close. */
	if (obj->handle_count == 0) {
		ret = -ENOENT;
		goto err;
	}

	if (!obj->name) {
		ret = idr_alloc(&dev->object_name_idr, obj, 1, 0, GFP_NOWAIT);
		if (ret < 0)
			goto err;

		obj->name = ret;

		/* Allocate a reference for the name table.  */
		drm_gem_object_reference(obj);
	}

	args->name = (uint64_t) obj->name;
	ret = 0;

err:
	lockmgr(&dev->object_name_lock, LK_RELEASE);
	idr_preload_end();
	drm_gem_object_unreference_unlocked(obj);
	return ret;
}

/**
 * drm_gem_open - implementation of the GEM_OPEN ioctl
 * @dev: drm_device
 * @data: ioctl data
 * @file_priv: drm file-private structure
 *
 * Open an object using the global name, returning a handle and the size.
 *
 * This handle (of course) holds a reference to the object, so the object
 * will not go away until the handle is deleted.
 */
int
drm_gem_open_ioctl(struct drm_device *dev, void *data,
		   struct drm_file *file_priv)
{
	struct drm_gem_open *args = data;
	struct drm_gem_object *obj;
	int ret;
	u32 handle;

	if (!drm_core_check_feature(dev, DRIVER_GEM))
		return -ENODEV;

	lockmgr(&dev->object_name_lock, LK_EXCLUSIVE);
	obj = idr_find(&dev->object_name_idr, (int) args->name);
	if (obj)
		drm_gem_object_reference(obj);
	lockmgr(&dev->object_name_lock, LK_RELEASE);
	if (!obj)
		return -ENOENT;

	ret = drm_gem_handle_create(file_priv, obj, &handle);
	drm_gem_object_unreference_unlocked(obj);
	if (ret)
		return ret;

	args->handle = handle;
	args->size = obj->size;

	return 0;
}

/**
 * gem_gem_open - initalizes GEM file-private structures at devnode open time
 * @dev: drm_device which is being opened by userspace
 * @file_private: drm file-private structure to set up
 *
 * Called at device open time, sets up the structure for handling refcounting
 * of mm objects.
 */
void
drm_gem_open(struct drm_device *dev, struct drm_file *file_private)
{
	idr_init(&file_private->object_idr);
	lockinit(&file_private->table_lock, "fptab", 0, LK_CANRECURSE);
}

/*
 * Called at device close to release the file's
 * handle references on objects.
 */
static int
drm_gem_object_release_handle(int id, void *ptr, void *data)
{
	struct drm_file *file_priv = data;
	struct drm_gem_object *obj = ptr;
	struct drm_device *dev = obj->dev;

	drm_gem_remove_prime_handles(obj, file_priv);

	if (dev->driver->gem_close_object)
		dev->driver->gem_close_object(obj, file_priv);

	drm_gem_object_handle_unreference_unlocked(obj);

	return 0;
}

/**
 * drm_gem_release - release file-private GEM resources
 * @dev: drm_device which is being closed by userspace
 * @file_private: drm file-private structure to clean up
 *
 * Called at close time when the filp is going away.
 *
 * Releases any remaining references on objects by this filp.
 */
void
drm_gem_release(struct drm_device *dev, struct drm_file *file_private)
{
	idr_for_each(&file_private->object_idr,
		     &drm_gem_object_release_handle, file_private);
	idr_destroy(&file_private->object_idr);
}

void
drm_gem_object_release(struct drm_gem_object *obj)
{

	/*
	 * obj->vm_obj can be NULL for private gem objects.
	 */
	vm_object_deallocate(obj->vm_obj);
}
EXPORT_SYMBOL(drm_gem_object_release);

/**
 * drm_gem_object_free - free a GEM object
 * @kref: kref of the object to free
 *
 * Called after the last reference to the object has been lost.
 * Must be called holding struct_ mutex
 *
 * Frees the object
 */
void
drm_gem_object_free(struct kref *kref)
{
	struct drm_gem_object *obj =
		container_of(kref, struct drm_gem_object, refcount);
	struct drm_device *dev = obj->dev;

	WARN_ON(!mutex_is_locked(&dev->struct_mutex));

	if (dev->driver->gem_free_object != NULL)
		dev->driver->gem_free_object(obj);
}
EXPORT_SYMBOL(drm_gem_object_free);

static struct drm_gem_object *
drm_gem_object_from_offset(struct drm_device *dev, vm_ooffset_t offset)
{
	struct drm_gem_object *obj;
	struct drm_gem_mm *mm = dev->mm_private;
	struct drm_hash_item *hash;

	if ((offset & DRM_GEM_MAPPING_MASK) != DRM_GEM_MAPPING_KEY)
		return (NULL);
	offset &= ~DRM_GEM_MAPPING_KEY;

	if (drm_ht_find_item(&mm->offset_hash, DRM_GEM_MAPPING_IDX(offset),
	    &hash) != 0) {
		return (NULL);
	}
	obj = container_of(hash, struct drm_gem_object, map_list);
	return (obj);
}

int
drm_gem_mmap_single(struct drm_device *dev, vm_ooffset_t *offset, vm_size_t size,
    struct vm_object **obj_res, int nprot)
{
	struct drm_gem_object *gem_obj;
	struct vm_object *vm_obj;

	DRM_LOCK(dev);
	gem_obj = drm_gem_object_from_offset(dev, *offset);
	if (gem_obj == NULL) {
		DRM_UNLOCK(dev);
		return (ENODEV);
	}

	drm_gem_object_reference(gem_obj);
	DRM_UNLOCK(dev);
	vm_obj = cdev_pager_allocate(gem_obj, OBJT_MGTDEVICE,
	    dev->driver->gem_pager_ops, size, nprot,
	    DRM_GEM_MAPPING_MAPOFF(*offset), curthread->td_ucred);
	if (vm_obj == NULL) {
		drm_gem_object_unreference_unlocked(gem_obj);
		return (EINVAL);
	}
	*offset = DRM_GEM_MAPPING_MAPOFF(*offset);
	*obj_res = vm_obj;
	return (0);
}