drm/ttm/ttm_bo_vm.c

/**************************************************************************
 *
 * Copyright (c) 2006-2009 VMware, Inc., Palo Alto, CA., USA
 * All Rights Reserved.
 *
 * 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, sub license, 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 NON-INFRINGEMENT. IN NO EVENT SHALL
 * THE COPYRIGHT HOLDERS, AUTHORS AND/OR ITS SUPPLIERS 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: Thomas Hellstrom <thellstrom-at-vmware-dot-com>
 */

#define pr_fmt(fmt) "[TTM] " fmt

#include <ttm/ttm_module.h>
#include <ttm/ttm_bo_driver.h>
#include <ttm/ttm_bo_api.h>
#include <ttm/ttm_placement.h>
#include <drm/drm_vma_manager.h>
#include <linux/mm.h>
#include <linux/rbtree.h>
#include <linux/module.h>
#include <linux/uaccess.h>

#include <sys/sysctl.h>
#include <vm/vm.h>
#include <vm/vm_page.h>
#include <vm/vm_page2.h>

#define TTM_BO_VM_NUM_PREFAULT 16

/*
 * Always unstall on unexpected vm_page alias, fatal bus fault.
 * Set to 0 to stall, set to positive count to unstall N times,
 * then stall again.
 */
static int drm_unstall = -1;
SYSCTL_INT(_debug, OID_AUTO, unstall, CTLFLAG_RW, &drm_unstall, 0, "");

static int ttm_bo_vm_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
{
	/* see ttm_bo_mmap_single() at end of this file */
	/* ttm_bo_vm_ops not currently used, no entry should occur */
	panic("ttm_bo_vm_fault");
#if 0
	struct ttm_buffer_object *bo = (struct ttm_buffer_object *)
	    vma->vm_private_data;
	struct ttm_bo_device *bdev = bo->bdev;
	unsigned long page_offset;
	unsigned long page_last;
	unsigned long pfn;
	struct ttm_tt *ttm = NULL;
	struct page *page;
	int ret;
	int i;
	unsigned long address = (unsigned long)vmf->virtual_address;
	int retval = VM_FAULT_NOPAGE;
	struct ttm_mem_type_manager *man =
		&bdev->man[bo->mem.mem_type];

	/*
	 * Work around locking order reversal in fault / nopfn
	 * between mmap_sem and bo_reserve: Perform a trylock operation
	 * for reserve, and if it fails, retry the fault after scheduling.
	 */

	ret = ttm_bo_reserve(bo, true, true, false, 0);
	if (unlikely(ret != 0)) {
		if (ret == -EBUSY)
			set_need_resched();
		return VM_FAULT_NOPAGE;
	}

	if (bdev->driver->fault_reserve_notify) {
		ret = bdev->driver->fault_reserve_notify(bo);
		switch (ret) {
		case 0:
			break;
		case -EBUSY:
			set_need_resched();
		case -ERESTARTSYS:
			retval = VM_FAULT_NOPAGE;
			goto out_unlock;
		default:
			retval = VM_FAULT_SIGBUS;
			goto out_unlock;
		}
	}

	/*
	 * Wait for buffer data in transit, due to a pipelined
	 * move.
	 */

	lockmgr(&bdev->fence_lock, LK_EXCLUSIVE);
	if (test_bit(TTM_BO_PRIV_FLAG_MOVING, &bo->priv_flags)) {
		ret = ttm_bo_wait(bo, false, true, false);
		lockmgr(&bdev->fence_lock, LK_RELEASE);
		if (unlikely(ret != 0)) {
			retval = (ret != -ERESTARTSYS) ?
			    VM_FAULT_SIGBUS : VM_FAULT_NOPAGE;
			goto out_unlock;
		}
	} else
		lockmgr(&bdev->fence_lock, LK_RELEASE);

	ret = ttm_mem_io_lock(man, true);
	if (unlikely(ret != 0)) {
		retval = VM_FAULT_NOPAGE;
		goto out_unlock;
	}
	ret = ttm_mem_io_reserve_vm(bo);
	if (unlikely(ret != 0)) {
		retval = VM_FAULT_SIGBUS;
		goto out_io_unlock;
	}

	page_offset = ((address - vma->vm_start) >> PAGE_SHIFT) +
	    drm_vma_node_start(&bo->vma_node) - vma->vm_pgoff;
	page_last = vma_pages(vma) +
	    drm_vma_node_start(&bo->vma_node) - vma->vm_pgoff;

	if (unlikely(page_offset >= bo->num_pages)) {
		retval = VM_FAULT_SIGBUS;
		goto out_io_unlock;
	}

	/*
	 * Strictly, we're not allowed to modify vma->vm_page_prot here,
	 * since the mmap_sem is only held in read mode. However, we
	 * modify only the caching bits of vma->vm_page_prot and
	 * consider those bits protected by
	 * the bo->mutex, as we should be the only writers.
	 * There shouldn't really be any readers of these bits except
	 * within vm_insert_mixed()? fork?
	 *
	 * TODO: Add a list of vmas to the bo, and change the
	 * vma->vm_page_prot when the object changes caching policy, with
	 * the correct locks held.
	 */
	if (bo->mem.bus.is_iomem) {
		vma->vm_page_prot = ttm_io_prot(bo->mem.placement,
						vma->vm_page_prot);
	} else {
		ttm = bo->ttm;
		vma->vm_page_prot = (bo->mem.placement & TTM_PL_FLAG_CACHED) ?
		    vm_get_page_prot(vma->vm_flags) :
		    ttm_io_prot(bo->mem.placement, vma->vm_page_prot);

		/* Allocate all page at once, most common usage */
		if (ttm->bdev->driver->ttm_tt_populate(ttm)) {
			retval = VM_FAULT_OOM;
			goto out_io_unlock;
		}
	}

	/*
	 * Speculatively prefault a number of pages. Only error on
	 * first page.
	 */
	for (i = 0; i < TTM_BO_VM_NUM_PREFAULT; ++i) {
		if (bo->mem.bus.is_iomem)
			pfn = ((bo->mem.bus.base + bo->mem.bus.offset) >> PAGE_SHIFT) + page_offset;
		else {
			page = ttm->pages[page_offset];
			if (unlikely(!page && i == 0)) {
				retval = VM_FAULT_OOM;
				goto out_io_unlock;
			} else if (unlikely(!page)) {
				break;
			}
			pfn = page_to_pfn(page);
		}

		ret = vm_insert_mixed(vma, address, pfn);
		/*
		 * Somebody beat us to this PTE or prefaulting to
		 * an already populated PTE, or prefaulting error.
		 */

		if (unlikely((ret == -EBUSY) || (ret != 0 && i > 0)))
			break;
		else if (unlikely(ret != 0)) {
			retval =
			    (ret == -ENOMEM) ? VM_FAULT_OOM : VM_FAULT_SIGBUS;
			goto out_io_unlock;
		}

		address += PAGE_SIZE;
		if (unlikely(++page_offset >= page_last))
			break;
	}
out_io_unlock:
	ttm_mem_io_unlock(man);
out_unlock:
	ttm_bo_unreserve(bo);
	return retval;
#endif
}

/* ttm_bo_vm_ops not currently used, no entry should occur */
static void ttm_bo_vm_open(struct vm_area_struct *vma)
{
	struct ttm_buffer_object *bo =
	    (struct ttm_buffer_object *)vma->vm_private_data;

	(void)ttm_bo_reference(bo);
}

/* ttm_bo_vm_ops not currently used, no entry should occur */
static void ttm_bo_vm_close(struct vm_area_struct *vma)
{
	struct ttm_buffer_object *bo = (struct ttm_buffer_object *)vma->vm_private_data;

	ttm_bo_unref(&bo);
	vma->vm_private_data = NULL;
}

static const struct vm_operations_struct ttm_bo_vm_ops = {
	.fault = ttm_bo_vm_fault,
	.open = ttm_bo_vm_open,
	.close = ttm_bo_vm_close
};

static struct ttm_buffer_object *ttm_bo_vm_lookup(struct ttm_bo_device *bdev,
						  unsigned long offset,
						  unsigned long pages)
{
	struct drm_vma_offset_node *node;
	struct ttm_buffer_object *bo = NULL;

	drm_vma_offset_lock_lookup(&bdev->vma_manager);

	node = drm_vma_offset_lookup_locked(&bdev->vma_manager, offset, pages);
	if (likely(node)) {
		bo = container_of(node, struct ttm_buffer_object, vma_node);
		if (!kref_get_unless_zero(&bo->kref))
			bo = NULL;
	}

	drm_vma_offset_unlock_lookup(&bdev->vma_manager);

	if (!bo)
		pr_err("Could not find buffer object to map\n");

	return bo;
}

int ttm_bo_mmap(struct file *filp, struct vm_area_struct *vma,
		struct ttm_bo_device *bdev)
{
	struct ttm_bo_driver *driver;
	struct ttm_buffer_object *bo;
	int ret;

	bo = ttm_bo_vm_lookup(bdev, vma->vm_pgoff, vma_pages(vma));
	if (unlikely(!bo))
		return -EINVAL;

	driver = bo->bdev->driver;
	if (unlikely(!driver->verify_access)) {
		ret = -EPERM;
		goto out_unref;
	}
	ret = driver->verify_access(bo, filp);
	if (unlikely(ret != 0))
		goto out_unref;

	vma->vm_ops = &ttm_bo_vm_ops;

	/*
	 * Note: We're transferring the bo reference to
	 * vma->vm_private_data here.
	 */

	vma->vm_private_data = bo;
	vma->vm_flags |= VM_IO | VM_MIXEDMAP | VM_DONTEXPAND | VM_DONTDUMP;
	return 0;
out_unref:
	ttm_bo_unref(&bo);
	return ret;
}
EXPORT_SYMBOL(ttm_bo_mmap);

int ttm_fbdev_mmap(struct vm_area_struct *vma, struct ttm_buffer_object *bo)
{
	if (vma->vm_pgoff != 0)
		return -EACCES;

	vma->vm_ops = &ttm_bo_vm_ops;
	vma->vm_private_data = ttm_bo_reference(bo);
	vma->vm_flags |= VM_IO | VM_MIXEDMAP | VM_DONTEXPAND;
	return 0;
}
EXPORT_SYMBOL(ttm_fbdev_mmap);


ssize_t ttm_bo_io(struct ttm_bo_device *bdev, struct file *filp,
		  const char __user *wbuf, char __user *rbuf, size_t count,
		  loff_t *f_pos, bool write)
{
	struct ttm_buffer_object *bo;
	struct ttm_bo_driver *driver;
	struct ttm_bo_kmap_obj map;
	unsigned long dev_offset = (*f_pos >> PAGE_SHIFT);
	unsigned long kmap_offset;
	unsigned long kmap_end;
	unsigned long kmap_num;
	size_t io_size;
	unsigned int page_offset;
	char *virtual;
	int ret;
	bool no_wait = false;
	bool dummy;

	bo = ttm_bo_vm_lookup(bdev, dev_offset, 1);
	if (unlikely(bo == NULL))
		return -EFAULT;

	driver = bo->bdev->driver;
	if (unlikely(!driver->verify_access)) {
		ret = -EPERM;
		goto out_unref;
	}

	ret = driver->verify_access(bo, filp);
	if (unlikely(ret != 0))
		goto out_unref;

	kmap_offset = dev_offset - drm_vma_node_start(&bo->vma_node);
	if (unlikely(kmap_offset >= bo->num_pages)) {
		ret = -EFBIG;
		goto out_unref;
	}

	page_offset = *f_pos & ~PAGE_MASK;
	io_size = bo->num_pages - kmap_offset;
	io_size = (io_size << PAGE_SHIFT) - page_offset;
	if (count < io_size)
		io_size = count;

	kmap_end = (*f_pos + count - 1) >> PAGE_SHIFT;
	kmap_num = kmap_end - kmap_offset + 1;

	ret = ttm_bo_reserve(bo, true, no_wait, false, 0);

	switch (ret) {
	case 0:
		break;
	case -EBUSY:
		ret = -EAGAIN;
		goto out_unref;
	default:
		goto out_unref;
	}

	ret = ttm_bo_kmap(bo, kmap_offset, kmap_num, &map);
	if (unlikely(ret != 0)) {
		ttm_bo_unreserve(bo);
		goto out_unref;
	}

	virtual = ttm_kmap_obj_virtual(&map, &dummy);
	virtual += page_offset;

	if (write)
		ret = copy_from_user(virtual, wbuf, io_size);
	else
		ret = copy_to_user(rbuf, virtual, io_size);

	ttm_bo_kunmap(&map);
	ttm_bo_unreserve(bo);
	ttm_bo_unref(&bo);

	if (unlikely(ret != 0))
		return -EFBIG;

	*f_pos += io_size;

	return io_size;
out_unref:
	ttm_bo_unref(&bo);
	return ret;
}

ssize_t ttm_bo_fbdev_io(struct ttm_buffer_object *bo, const char __user *wbuf,
			char __user *rbuf, size_t count, loff_t *f_pos,
			bool write)
{
	struct ttm_bo_kmap_obj map;
	unsigned long kmap_offset;
	unsigned long kmap_end;
	unsigned long kmap_num;
	size_t io_size;
	unsigned int page_offset;
	char *virtual;
	int ret;
	bool no_wait = false;
	bool dummy;

	kmap_offset = (*f_pos >> PAGE_SHIFT);
	if (unlikely(kmap_offset >= bo->num_pages))
		return -EFBIG;

	page_offset = *f_pos & ~PAGE_MASK;
	io_size = bo->num_pages - kmap_offset;
	io_size = (io_size << PAGE_SHIFT) - page_offset;
	if (count < io_size)
		io_size = count;

	kmap_end = (*f_pos + count - 1) >> PAGE_SHIFT;
	kmap_num = kmap_end - kmap_offset + 1;

	ret = ttm_bo_reserve(bo, true, no_wait, false, 0);

	switch (ret) {
	case 0:
		break;
	case -EBUSY:
		return -EAGAIN;
	default:
		return ret;
	}

	ret = ttm_bo_kmap(bo, kmap_offset, kmap_num, &map);
	if (unlikely(ret != 0)) {
		ttm_bo_unreserve(bo);
		return ret;
	}

	virtual = ttm_kmap_obj_virtual(&map, &dummy);
	virtual += page_offset;

	if (write)
		ret = copy_from_user(virtual, wbuf, io_size);
	else
		ret = copy_to_user(rbuf, virtual, io_size);

	ttm_bo_kunmap(&map);
	ttm_bo_unreserve(bo);
	ttm_bo_unref(&bo);

	if (unlikely(ret != 0))
		return ret;

	*f_pos += io_size;

	return io_size;
}

/*
 * DragonFlyBSD Interface
 */

#include "opt_vm.h"

#include <vm/vm.h>
#include <vm/vm_page.h>
#include <linux/errno.h>
#include <linux/export.h>

#include <vm/vm_page2.h>

static int
ttm_bo_vm_fault_dfly(vm_object_t vm_obj, vm_ooffset_t offset,
		     int prot, vm_page_t *mres)
{
	struct ttm_buffer_object *bo = vm_obj->handle;
	struct ttm_bo_device *bdev = bo->bdev;
	struct ttm_tt *ttm = NULL;
	vm_page_t m, oldm;
	int ret;
	int retval = VM_PAGER_OK;
	struct ttm_mem_type_manager *man;

	man = &bdev->man[bo->mem.mem_type];

	/*kprintf("FAULT %p %p/%ld\n", vm_obj, bo, offset);*/

	vm_object_pip_add(vm_obj, 1);
	oldm = *mres;
	*mres = NULL;

retry:
	VM_OBJECT_UNLOCK(vm_obj);
	m = NULL;

	/*
	 * NOTE: set nowait to false, we don't have ttm_bo_wait_unreserved()
	 * 	 for the -BUSY case yet.
	 */
	ret = ttm_bo_reserve(bo, true, false, false, 0);
	if (unlikely(ret != 0)) {
		retval = VM_PAGER_ERROR;
		VM_OBJECT_LOCK(vm_obj);
		goto out_unlock2;
	}

	if (bdev->driver->fault_reserve_notify) {
		ret = bdev->driver->fault_reserve_notify(bo);
		switch (ret) {
		case 0:
			break;
		case -EBUSY:
			lwkt_yield();
			/* fall through */
		case -ERESTARTSYS:
		case -EINTR:
			retval = VM_PAGER_ERROR;
			goto out_unlock;
		default:
			retval = VM_PAGER_ERROR;
			goto out_unlock;
		}
	}

	/*
	 * Wait for buffer data in transit, due to a pipelined
	 * move.
	 */
	lockmgr(&bdev->fence_lock, LK_EXCLUSIVE);
	if (test_bit(TTM_BO_PRIV_FLAG_MOVING, &bo->priv_flags)) {
		/*
		 * Here, the behavior differs between Linux and FreeBSD.
		 *
		 * On Linux, the wait is interruptible (3rd argument to
		 * ttm_bo_wait). There must be some mechanism to resume
		 * page fault handling, once the signal is processed.
		 *
		 * On FreeBSD, the wait is uninteruptible. This is not a
		 * problem as we can't end up with an unkillable process
		 * here, because the wait will eventually time out.
		 *
		 * An example of this situation is the Xorg process
		 * which uses SIGALRM internally. The signal could
		 * interrupt the wait, causing the page fault to fail
		 * and the process to receive SIGSEGV.
		 */
		ret = ttm_bo_wait(bo, false, false, false);
		lockmgr(&bdev->fence_lock, LK_RELEASE);
		if (unlikely(ret != 0)) {
			retval = VM_PAGER_ERROR;
			goto out_unlock;
		}
	} else {
		lockmgr(&bdev->fence_lock, LK_RELEASE);
	}

	ret = ttm_mem_io_lock(man, true);
	if (unlikely(ret != 0)) {
		retval = VM_PAGER_ERROR;
		goto out_unlock;
	}
	ret = ttm_mem_io_reserve_vm(bo);
	if (unlikely(ret != 0)) {
		retval = VM_PAGER_ERROR;
		goto out_io_unlock;
	}
	if (unlikely(OFF_TO_IDX(offset) >= bo->num_pages)) {
		retval = VM_PAGER_ERROR;
		goto out_io_unlock;
	}

	/*
	 * Strictly, we're not allowed to modify vma->vm_page_prot here,
	 * since the mmap_sem is only held in read mode. However, we
	 * modify only the caching bits of vma->vm_page_prot and
	 * consider those bits protected by
	 * the bo->mutex, as we should be the only writers.
	 * There shouldn't really be any readers of these bits except
	 * within vm_insert_mixed()? fork?
	 *
	 * TODO: Add a list of vmas to the bo, and change the
	 * vma->vm_page_prot when the object changes caching policy, with
	 * the correct locks held.
	 */

	if (bo->mem.bus.is_iomem) {
		m = vm_phys_fictitious_to_vm_page(bo->mem.bus.base +
						  bo->mem.bus.offset + offset);
		pmap_page_set_memattr(m, ttm_io_prot(bo->mem.placement, 0));
	} else {
		/* Allocate all page at once, most common usage */
		ttm = bo->ttm;
		if (ttm->bdev->driver->ttm_tt_populate(ttm)) {
			retval = VM_PAGER_ERROR;
			goto out_io_unlock;
		}
		ttm = bo->ttm;

		m = (struct vm_page *)ttm->pages[OFF_TO_IDX(offset)];
		if (unlikely(!m)) {
			retval = VM_PAGER_ERROR;
			goto out_io_unlock;
		}
		pmap_page_set_memattr(m,
		    (bo->mem.placement & TTM_PL_FLAG_CACHED) ?
		    VM_MEMATTR_WRITE_BACK : ttm_io_prot(bo->mem.placement, 0));
	}

	VM_OBJECT_LOCK(vm_obj);

	if (vm_page_busy_try(m, FALSE)) {
		kprintf("r");
		vm_page_sleep_busy(m, FALSE, "ttmvmf");
		ttm_mem_io_unlock(man);
		ttm_bo_unreserve(bo);
		goto retry;
	}

	/*
	 * We want our fake page in the VM object, not the page the OS
	 * allocatedd for us as a placeholder.
	 */
	m->valid = VM_PAGE_BITS_ALL;
	*mres = m;
	if (oldm != NULL) {
		vm_page_remove(oldm);
		if (m->object) {
			retval = VM_PAGER_ERROR;
			kprintf("ttm_bo_vm_fault_dfly: m(%p) already inserted "
				"in obj %p, attempt obj %p\n",
				m, m->object, vm_obj);
			while (drm_unstall == 0) {
				tsleep(&retval, 0, "DEBUG", hz/10);
			}
			if (drm_unstall > 0)
				--drm_unstall;
		} else {
			vm_page_insert(m, vm_obj, OFF_TO_IDX(offset));
		}
		vm_page_free(oldm);
		oldm = NULL;
	} else {
		vm_page_t mtmp;

		kprintf("oldm NULL\n");

		mtmp = vm_page_lookup(vm_obj, OFF_TO_IDX(offset));
		KASSERT(mtmp == NULL || mtmp == m,
		    ("inconsistent insert bo %p m %p mtmp %p offset %jx",
		    bo, m, mtmp, (uintmax_t)offset));
		if (mtmp == NULL)
			vm_page_insert(m, vm_obj, OFF_TO_IDX(offset));
	}
	/*vm_page_busy_try(m, FALSE);*/

out_io_unlock1:
	ttm_mem_io_unlock(man);
out_unlock1:
	ttm_bo_unreserve(bo);
out_unlock2:
	if (oldm) {
		vm_page_remove(oldm);
		vm_page_free(oldm);
	}
	vm_object_pip_wakeup(vm_obj);
	return (retval);

out_io_unlock:
	VM_OBJECT_LOCK(vm_obj);
	goto out_io_unlock1;

out_unlock:
	VM_OBJECT_LOCK(vm_obj);
	goto out_unlock1;
}

static int
ttm_bo_vm_ctor(void *handle, vm_ooffset_t size, vm_prot_t prot,
	       vm_ooffset_t foff, struct ucred *cred, u_short *color)
{

	/*
	 * On Linux, a reference to the buffer object is acquired here.
	 * The reason is that this function is not called when the
	 * mmap() is initialized, but only when a process forks for
	 * instance. Therefore on Linux, the reference on the bo is
	 * acquired either in ttm_bo_mmap() or ttm_bo_vm_open(). It's
	 * then released in ttm_bo_vm_close().
	 *
	 * Here, this function is called during mmap() intialization.
	 * Thus, the reference acquired in ttm_bo_mmap_single() is
	 * sufficient.
	 */
	*color = 0;
	return (0);
}

static void
ttm_bo_vm_dtor(void *handle)
{
	struct ttm_buffer_object *bo = handle;

	ttm_bo_unref(&bo);
}

static struct cdev_pager_ops ttm_pager_ops = {
	.cdev_pg_fault = ttm_bo_vm_fault_dfly,
	.cdev_pg_ctor = ttm_bo_vm_ctor,
	.cdev_pg_dtor = ttm_bo_vm_dtor
};

/*
 * Called from drm_drv.c
 *
 * *offset - object offset in bytes
 * size	   - map size in bytes
 *
 * We setup a dummy vma (for now) and call ttm_bo_mmap().  Then we setup
 * our own VM object and dfly ops.  Note that the ops supplied by
 * ttm_bo_mmap() are not currently used.
 */
int
ttm_bo_mmap_single(struct drm_device *dev, vm_ooffset_t *offset,
		   vm_size_t size, struct vm_object **obj_res, int nprot)
{
	struct ttm_bo_device *bdev = dev->drm_ttm_bdev;
	struct ttm_buffer_object *bo;
	struct vm_object *vm_obj;
	struct vm_area_struct vma;
	int ret;

	*obj_res = NULL;

	bzero(&vma, sizeof(vma));
	vma.vm_start = *offset;		/* bdev-relative offset */
	vma.vm_end = vma.vm_start + size;
	vma.vm_pgoff = vma.vm_start >> PAGE_SHIFT;
	/* vma.vm_page_prot */
	/* vma.vm_flags */

	/*
	 * Call the linux-ported code to do the work, and on success just
	 * setup our own VM object and ignore what the linux code did other
	 * then supplying us the 'bo'.
	 */
	ret = ttm_bo_mmap(NULL, &vma, bdev);

	if (ret == 0) {
		bo = vma.vm_private_data;
		vm_obj = cdev_pager_allocate(bo, OBJT_MGTDEVICE,
					     &ttm_pager_ops,
					     size, nprot, 0,
					     curthread->td_ucred);
		if (vm_obj) {
			*obj_res = vm_obj;
			*offset = 0;		/* object-relative offset */
		} else {
			ttm_bo_unref(&bo);
			ret = EINVAL;
		}
	}
	return ret;
}
EXPORT_SYMBOL(ttm_bo_mmap_single);

void
ttm_bo_release_mmap(struct ttm_buffer_object *bo)
{
	vm_object_t vm_obj;
	vm_page_t m;
	int i;

	vm_obj = cdev_pager_lookup(bo);
	if (vm_obj == NULL)
		return;

	VM_OBJECT_LOCK(vm_obj);
	for (i = 0; i < bo->num_pages; i++) {
		m = vm_page_lookup_busy_wait(vm_obj, i, TRUE, "ttm_unm");
		if (m == NULL)
			continue;
		cdev_pager_free_page(vm_obj, m);
	}
	VM_OBJECT_UNLOCK(vm_obj);

	vm_object_deallocate(vm_obj);
}

#if 0
int ttm_fbdev_mmap(struct vm_area_struct *vma, struct ttm_buffer_object *bo)
{
	if (vma->vm_pgoff != 0)
		return -EACCES;

	vma->vm_ops = &ttm_bo_vm_ops;
	vma->vm_private_data = ttm_bo_reference(bo);
	vma->vm_flags |= VM_IO | VM_MIXEDMAP | VM_DONTEXPAND;
	return 0;
}
EXPORT_SYMBOL(ttm_fbdev_mmap);
#endif