summaryrefslogtreecommitdiff
path: root/drivers/xen/gntdev-dmabuf.c
blob: 940e5e9e8a54a7391de26509348b95aadf8b1f27 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
// SPDX-License-Identifier: GPL-2.0

/*
 * Xen dma-buf functionality for gntdev.
 *
 * DMA buffer implementation is based on drivers/gpu/drm/drm_prime.c.
 *
 * Copyright (c) 2018 Oleksandr Andrushchenko, EPAM Systems Inc.
 */

#include <linux/kernel.h>
#include <linux/errno.h>
#include <linux/dma-buf.h>
#include <linux/slab.h>
#include <linux/types.h>
#include <linux/uaccess.h>
#include <linux/module.h>

#include <xen/xen.h>
#include <xen/grant_table.h>

#include "gntdev-common.h"
#include "gntdev-dmabuf.h"

MODULE_IMPORT_NS(DMA_BUF);

struct gntdev_dmabuf {
	struct gntdev_dmabuf_priv *priv;
	struct dma_buf *dmabuf;
	struct list_head next;
	int fd;

	union {
		struct {
			/* Exported buffers are reference counted. */
			struct kref refcount;

			struct gntdev_priv *priv;
			struct gntdev_grant_map *map;
		} exp;
		struct {
			/* Granted references of the imported buffer. */
			grant_ref_t *refs;
			/* Scatter-gather table of the imported buffer. */
			struct sg_table *sgt;
			/* dma-buf attachment of the imported buffer. */
			struct dma_buf_attachment *attach;
		} imp;
	} u;

	/* Number of pages this buffer has. */
	int nr_pages;
	/* Pages of this buffer. */
	struct page **pages;
};

struct gntdev_dmabuf_wait_obj {
	struct list_head next;
	struct gntdev_dmabuf *gntdev_dmabuf;
	struct completion completion;
};

struct gntdev_dmabuf_attachment {
	struct sg_table *sgt;
	enum dma_data_direction dir;
};

struct gntdev_dmabuf_priv {
	/* List of exported DMA buffers. */
	struct list_head exp_list;
	/* List of wait objects. */
	struct list_head exp_wait_list;
	/* List of imported DMA buffers. */
	struct list_head imp_list;
	/* This is the lock which protects dma_buf_xxx lists. */
	struct mutex lock;
	/*
	 * We reference this file while exporting dma-bufs, so
	 * the grant device context is not destroyed while there are
	 * external users alive.
	 */
	struct file *filp;
};

/* DMA buffer export support. */

/* Implementation of wait for exported DMA buffer to be released. */

static void dmabuf_exp_release(struct kref *kref);

static struct gntdev_dmabuf_wait_obj *
dmabuf_exp_wait_obj_new(struct gntdev_dmabuf_priv *priv,
			struct gntdev_dmabuf *gntdev_dmabuf)
{
	struct gntdev_dmabuf_wait_obj *obj;

	obj = kzalloc(sizeof(*obj), GFP_KERNEL);
	if (!obj)
		return ERR_PTR(-ENOMEM);

	init_completion(&obj->completion);
	obj->gntdev_dmabuf = gntdev_dmabuf;

	mutex_lock(&priv->lock);
	list_add(&obj->next, &priv->exp_wait_list);
	/* Put our reference and wait for gntdev_dmabuf's release to fire. */
	kref_put(&gntdev_dmabuf->u.exp.refcount, dmabuf_exp_release);
	mutex_unlock(&priv->lock);
	return obj;
}

static void dmabuf_exp_wait_obj_free(struct gntdev_dmabuf_priv *priv,
				     struct gntdev_dmabuf_wait_obj *obj)
{
	mutex_lock(&priv->lock);
	list_del(&obj->next);
	mutex_unlock(&priv->lock);
	kfree(obj);
}

static int dmabuf_exp_wait_obj_wait(struct gntdev_dmabuf_wait_obj *obj,
				    u32 wait_to_ms)
{
	if (wait_for_completion_timeout(&obj->completion,
			msecs_to_jiffies(wait_to_ms)) <= 0)
		return -ETIMEDOUT;

	return 0;
}

static void dmabuf_exp_wait_obj_signal(struct gntdev_dmabuf_priv *priv,
				       struct gntdev_dmabuf *gntdev_dmabuf)
{
	struct gntdev_dmabuf_wait_obj *obj;

	list_for_each_entry(obj, &priv->exp_wait_list, next)
		if (obj->gntdev_dmabuf == gntdev_dmabuf) {
			pr_debug("Found gntdev_dmabuf in the wait list, wake\n");
			complete_all(&obj->completion);
			break;
		}
}

static struct gntdev_dmabuf *
dmabuf_exp_wait_obj_get_dmabuf(struct gntdev_dmabuf_priv *priv, int fd)
{
	struct gntdev_dmabuf *gntdev_dmabuf, *ret = ERR_PTR(-ENOENT);

	mutex_lock(&priv->lock);
	list_for_each_entry(gntdev_dmabuf, &priv->exp_list, next)
		if (gntdev_dmabuf->fd == fd) {
			pr_debug("Found gntdev_dmabuf in the wait list\n");
			kref_get(&gntdev_dmabuf->u.exp.refcount);
			ret = gntdev_dmabuf;
			break;
		}
	mutex_unlock(&priv->lock);
	return ret;
}

static int dmabuf_exp_wait_released(struct gntdev_dmabuf_priv *priv, int fd,
				    int wait_to_ms)
{
	struct gntdev_dmabuf *gntdev_dmabuf;
	struct gntdev_dmabuf_wait_obj *obj;
	int ret;

	pr_debug("Will wait for dma-buf with fd %d\n", fd);
	/*
	 * Try to find the DMA buffer: if not found means that
	 * either the buffer has already been released or file descriptor
	 * provided is wrong.
	 */
	gntdev_dmabuf = dmabuf_exp_wait_obj_get_dmabuf(priv, fd);
	if (IS_ERR(gntdev_dmabuf))
		return PTR_ERR(gntdev_dmabuf);

	/*
	 * gntdev_dmabuf still exists and is reference count locked by us now,
	 * so prepare to wait: allocate wait object and add it to the wait list,
	 * so we can find it on release.
	 */
	obj = dmabuf_exp_wait_obj_new(priv, gntdev_dmabuf);
	if (IS_ERR(obj))
		return PTR_ERR(obj);

	ret = dmabuf_exp_wait_obj_wait(obj, wait_to_ms);
	dmabuf_exp_wait_obj_free(priv, obj);
	return ret;
}

/* DMA buffer export support. */

static struct sg_table *
dmabuf_pages_to_sgt(struct page **pages, unsigned int nr_pages)
{
	struct sg_table *sgt;
	int ret;

	sgt = kmalloc(sizeof(*sgt), GFP_KERNEL);
	if (!sgt) {
		ret = -ENOMEM;
		goto out;
	}

	ret = sg_alloc_table_from_pages(sgt, pages, nr_pages, 0,
					nr_pages << PAGE_SHIFT,
					GFP_KERNEL);
	if (ret)
		goto out;

	return sgt;

out:
	kfree(sgt);
	return ERR_PTR(ret);
}

static int dmabuf_exp_ops_attach(struct dma_buf *dma_buf,
				 struct dma_buf_attachment *attach)
{
	struct gntdev_dmabuf_attachment *gntdev_dmabuf_attach;

	gntdev_dmabuf_attach = kzalloc(sizeof(*gntdev_dmabuf_attach),
				       GFP_KERNEL);
	if (!gntdev_dmabuf_attach)
		return -ENOMEM;

	gntdev_dmabuf_attach->dir = DMA_NONE;
	attach->priv = gntdev_dmabuf_attach;
	return 0;
}

static void dmabuf_exp_ops_detach(struct dma_buf *dma_buf,
				  struct dma_buf_attachment *attach)
{
	struct gntdev_dmabuf_attachment *gntdev_dmabuf_attach = attach->priv;

	if (gntdev_dmabuf_attach) {
		struct sg_table *sgt = gntdev_dmabuf_attach->sgt;

		if (sgt) {
			if (gntdev_dmabuf_attach->dir != DMA_NONE)
				dma_unmap_sgtable(attach->dev, sgt,
						  gntdev_dmabuf_attach->dir,
						  DMA_ATTR_SKIP_CPU_SYNC);
			sg_free_table(sgt);
		}

		kfree(sgt);
		kfree(gntdev_dmabuf_attach);
		attach->priv = NULL;
	}
}

static struct sg_table *
dmabuf_exp_ops_map_dma_buf(struct dma_buf_attachment *attach,
			   enum dma_data_direction dir)
{
	struct gntdev_dmabuf_attachment *gntdev_dmabuf_attach = attach->priv;
	struct gntdev_dmabuf *gntdev_dmabuf = attach->dmabuf->priv;
	struct sg_table *sgt;

	pr_debug("Mapping %d pages for dev %p\n", gntdev_dmabuf->nr_pages,
		 attach->dev);

	if (dir == DMA_NONE || !gntdev_dmabuf_attach)
		return ERR_PTR(-EINVAL);

	/* Return the cached mapping when possible. */
	if (gntdev_dmabuf_attach->dir == dir)
		return gntdev_dmabuf_attach->sgt;

	/*
	 * Two mappings with different directions for the same attachment are
	 * not allowed.
	 */
	if (gntdev_dmabuf_attach->dir != DMA_NONE)
		return ERR_PTR(-EBUSY);

	sgt = dmabuf_pages_to_sgt(gntdev_dmabuf->pages,
				  gntdev_dmabuf->nr_pages);
	if (!IS_ERR(sgt)) {
		if (dma_map_sgtable(attach->dev, sgt, dir,
				    DMA_ATTR_SKIP_CPU_SYNC)) {
			sg_free_table(sgt);
			kfree(sgt);
			sgt = ERR_PTR(-ENOMEM);
		} else {
			gntdev_dmabuf_attach->sgt = sgt;
			gntdev_dmabuf_attach->dir = dir;
		}
	}
	if (IS_ERR(sgt))
		pr_debug("Failed to map sg table for dev %p\n", attach->dev);
	return sgt;
}

static void dmabuf_exp_ops_unmap_dma_buf(struct dma_buf_attachment *attach,
					 struct sg_table *sgt,
					 enum dma_data_direction dir)
{
	/* Not implemented. The unmap is done at dmabuf_exp_ops_detach(). */
}

static void dmabuf_exp_release(struct kref *kref)
{
	struct gntdev_dmabuf *gntdev_dmabuf =
		container_of(kref, struct gntdev_dmabuf, u.exp.refcount);

	dmabuf_exp_wait_obj_signal(gntdev_dmabuf->priv, gntdev_dmabuf);
	list_del(&gntdev_dmabuf->next);
	fput(gntdev_dmabuf->priv->filp);
	kfree(gntdev_dmabuf);
}

static void dmabuf_exp_remove_map(struct gntdev_priv *priv,
				  struct gntdev_grant_map *map)
{
	mutex_lock(&priv->lock);
	list_del(&map->next);
	gntdev_put_map(NULL /* already removed */, map);
	mutex_unlock(&priv->lock);
}

static void dmabuf_exp_ops_release(struct dma_buf *dma_buf)
{
	struct gntdev_dmabuf *gntdev_dmabuf = dma_buf->priv;
	struct gntdev_dmabuf_priv *priv = gntdev_dmabuf->priv;

	dmabuf_exp_remove_map(gntdev_dmabuf->u.exp.priv,
			      gntdev_dmabuf->u.exp.map);
	mutex_lock(&priv->lock);
	kref_put(&gntdev_dmabuf->u.exp.refcount, dmabuf_exp_release);
	mutex_unlock(&priv->lock);
}

static const struct dma_buf_ops dmabuf_exp_ops =  {
	.attach = dmabuf_exp_ops_attach,
	.detach = dmabuf_exp_ops_detach,
	.map_dma_buf = dmabuf_exp_ops_map_dma_buf,
	.unmap_dma_buf = dmabuf_exp_ops_unmap_dma_buf,
	.release = dmabuf_exp_ops_release,
};

struct gntdev_dmabuf_export_args {
	struct gntdev_priv *priv;
	struct gntdev_grant_map *map;
	struct gntdev_dmabuf_priv *dmabuf_priv;
	struct device *dev;
	int count;
	struct page **pages;
	u32 fd;
};

static int dmabuf_exp_from_pages(struct gntdev_dmabuf_export_args *args)
{
	DEFINE_DMA_BUF_EXPORT_INFO(exp_info);
	struct gntdev_dmabuf *gntdev_dmabuf;
	int ret;

	gntdev_dmabuf = kzalloc(sizeof(*gntdev_dmabuf), GFP_KERNEL);
	if (!gntdev_dmabuf)
		return -ENOMEM;

	kref_init(&gntdev_dmabuf->u.exp.refcount);

	gntdev_dmabuf->priv = args->dmabuf_priv;
	gntdev_dmabuf->nr_pages = args->count;
	gntdev_dmabuf->pages = args->pages;
	gntdev_dmabuf->u.exp.priv = args->priv;
	gntdev_dmabuf->u.exp.map = args->map;

	exp_info.exp_name = KBUILD_MODNAME;
	if (args->dev->driver && args->dev->driver->owner)
		exp_info.owner = args->dev->driver->owner;
	else
		exp_info.owner = THIS_MODULE;
	exp_info.ops = &dmabuf_exp_ops;
	exp_info.size = args->count << PAGE_SHIFT;
	exp_info.flags = O_RDWR;
	exp_info.priv = gntdev_dmabuf;

	gntdev_dmabuf->dmabuf = dma_buf_export(&exp_info);
	if (IS_ERR(gntdev_dmabuf->dmabuf)) {
		ret = PTR_ERR(gntdev_dmabuf->dmabuf);
		gntdev_dmabuf->dmabuf = NULL;
		goto fail;
	}

	ret = dma_buf_fd(gntdev_dmabuf->dmabuf, O_CLOEXEC);
	if (ret < 0)
		goto fail;

	gntdev_dmabuf->fd = ret;
	args->fd = ret;

	pr_debug("Exporting DMA buffer with fd %d\n", ret);

	mutex_lock(&args->dmabuf_priv->lock);
	list_add(&gntdev_dmabuf->next, &args->dmabuf_priv->exp_list);
	mutex_unlock(&args->dmabuf_priv->lock);
	get_file(gntdev_dmabuf->priv->filp);
	return 0;

fail:
	if (gntdev_dmabuf->dmabuf)
		dma_buf_put(gntdev_dmabuf->dmabuf);
	kfree(gntdev_dmabuf);
	return ret;
}

static struct gntdev_grant_map *
dmabuf_exp_alloc_backing_storage(struct gntdev_priv *priv, int dmabuf_flags,
				 int count)
{
	struct gntdev_grant_map *map;

	if (unlikely(gntdev_test_page_count(count)))
		return ERR_PTR(-EINVAL);

	if ((dmabuf_flags & GNTDEV_DMA_FLAG_WC) &&
	    (dmabuf_flags & GNTDEV_DMA_FLAG_COHERENT)) {
		pr_debug("Wrong dma-buf flags: 0x%x\n", dmabuf_flags);
		return ERR_PTR(-EINVAL);
	}

	map = gntdev_alloc_map(priv, count, dmabuf_flags);
	if (!map)
		return ERR_PTR(-ENOMEM);

	return map;
}

static int dmabuf_exp_from_refs(struct gntdev_priv *priv, int flags,
				int count, u32 domid, u32 *refs, u32 *fd)
{
	struct gntdev_grant_map *map;
	struct gntdev_dmabuf_export_args args;
	int i, ret;

	map = dmabuf_exp_alloc_backing_storage(priv, flags, count);
	if (IS_ERR(map))
		return PTR_ERR(map);

	for (i = 0; i < count; i++) {
		map->grants[i].domid = domid;
		map->grants[i].ref = refs[i];
	}

	mutex_lock(&priv->lock);
	gntdev_add_map(priv, map);
	mutex_unlock(&priv->lock);

	map->flags |= GNTMAP_host_map;
#if defined(CONFIG_X86)
	map->flags |= GNTMAP_device_map;
#endif

	ret = gntdev_map_grant_pages(map);
	if (ret < 0)
		goto out;

	args.priv = priv;
	args.map = map;
	args.dev = priv->dma_dev;
	args.dmabuf_priv = priv->dmabuf_priv;
	args.count = map->count;
	args.pages = map->pages;
	args.fd = -1; /* Shut up unnecessary gcc warning for i386 */

	ret = dmabuf_exp_from_pages(&args);
	if (ret < 0)
		goto out;

	*fd = args.fd;
	return 0;

out:
	dmabuf_exp_remove_map(priv, map);
	return ret;
}

/* DMA buffer import support. */

static int
dmabuf_imp_grant_foreign_access(struct page **pages, u32 *refs,
				int count, int domid)
{
	grant_ref_t priv_gref_head;
	int i, ret;

	ret = gnttab_alloc_grant_references(count, &priv_gref_head);
	if (ret < 0) {
		pr_debug("Cannot allocate grant references, ret %d\n", ret);
		return ret;
	}

	for (i = 0; i < count; i++) {
		int cur_ref;

		cur_ref = gnttab_claim_grant_reference(&priv_gref_head);
		if (cur_ref < 0) {
			ret = cur_ref;
			pr_debug("Cannot claim grant reference, ret %d\n", ret);
			goto out;
		}

		gnttab_grant_foreign_access_ref(cur_ref, domid,
						xen_page_to_gfn(pages[i]), 0);
		refs[i] = cur_ref;
	}

	return 0;

out:
	gnttab_free_grant_references(priv_gref_head);
	return ret;
}

static void dmabuf_imp_end_foreign_access(u32 *refs, int count)
{
	int i;

	for (i = 0; i < count; i++)
		if (refs[i] != INVALID_GRANT_REF)
			gnttab_end_foreign_access(refs[i], NULL);
}

static void dmabuf_imp_free_storage(struct gntdev_dmabuf *gntdev_dmabuf)
{
	kfree(gntdev_dmabuf->pages);
	kfree(gntdev_dmabuf->u.imp.refs);
	kfree(gntdev_dmabuf);
}

static struct gntdev_dmabuf *dmabuf_imp_alloc_storage(int count)
{
	struct gntdev_dmabuf *gntdev_dmabuf;
	int i;

	gntdev_dmabuf = kzalloc(sizeof(*gntdev_dmabuf), GFP_KERNEL);
	if (!gntdev_dmabuf)
		goto fail_no_free;

	gntdev_dmabuf->u.imp.refs = kcalloc(count,
					    sizeof(gntdev_dmabuf->u.imp.refs[0]),
					    GFP_KERNEL);
	if (!gntdev_dmabuf->u.imp.refs)
		goto fail;

	gntdev_dmabuf->pages = kcalloc(count,
				       sizeof(gntdev_dmabuf->pages[0]),
				       GFP_KERNEL);
	if (!gntdev_dmabuf->pages)
		goto fail;

	gntdev_dmabuf->nr_pages = count;

	for (i = 0; i < count; i++)
		gntdev_dmabuf->u.imp.refs[i] = INVALID_GRANT_REF;

	return gntdev_dmabuf;

fail:
	dmabuf_imp_free_storage(gntdev_dmabuf);
fail_no_free:
	return ERR_PTR(-ENOMEM);
}

static struct gntdev_dmabuf *
dmabuf_imp_to_refs(struct gntdev_dmabuf_priv *priv, struct device *dev,
		   int fd, int count, int domid)
{
	struct gntdev_dmabuf *gntdev_dmabuf, *ret;
	struct dma_buf *dma_buf;
	struct dma_buf_attachment *attach;
	struct sg_table *sgt;
	struct sg_page_iter sg_iter;
	int i;

	dma_buf = dma_buf_get(fd);
	if (IS_ERR(dma_buf))
		return ERR_CAST(dma_buf);

	gntdev_dmabuf = dmabuf_imp_alloc_storage(count);
	if (IS_ERR(gntdev_dmabuf)) {
		ret = gntdev_dmabuf;
		goto fail_put;
	}

	gntdev_dmabuf->priv = priv;
	gntdev_dmabuf->fd = fd;

	attach = dma_buf_attach(dma_buf, dev);
	if (IS_ERR(attach)) {
		ret = ERR_CAST(attach);
		goto fail_free_obj;
	}

	gntdev_dmabuf->u.imp.attach = attach;

	sgt = dma_buf_map_attachment(attach, DMA_BIDIRECTIONAL);
	if (IS_ERR(sgt)) {
		ret = ERR_CAST(sgt);
		goto fail_detach;
	}

	/* Check that we have zero offset. */
	if (sgt->sgl->offset) {
		ret = ERR_PTR(-EINVAL);
		pr_debug("DMA buffer has %d bytes offset, user-space expects 0\n",
			 sgt->sgl->offset);
		goto fail_unmap;
	}

	/* Check number of pages that imported buffer has. */
	if (attach->dmabuf->size != gntdev_dmabuf->nr_pages << PAGE_SHIFT) {
		ret = ERR_PTR(-EINVAL);
		pr_debug("DMA buffer has %zu pages, user-space expects %d\n",
			 attach->dmabuf->size, gntdev_dmabuf->nr_pages);
		goto fail_unmap;
	}

	gntdev_dmabuf->u.imp.sgt = sgt;

	/* Now convert sgt to array of pages and check for page validity. */
	i = 0;
	for_each_sgtable_page(sgt, &sg_iter, 0) {
		struct page *page = sg_page_iter_page(&sg_iter);
		/*
		 * Check if page is valid: this can happen if we are given
		 * a page from VRAM or other resources which are not backed
		 * by a struct page.
		 */
		if (!pfn_valid(page_to_pfn(page))) {
			ret = ERR_PTR(-EINVAL);
			goto fail_unmap;
		}

		gntdev_dmabuf->pages[i++] = page;
	}

	ret = ERR_PTR(dmabuf_imp_grant_foreign_access(gntdev_dmabuf->pages,
						      gntdev_dmabuf->u.imp.refs,
						      count, domid));
	if (IS_ERR(ret))
		goto fail_end_access;

	pr_debug("Imported DMA buffer with fd %d\n", fd);

	mutex_lock(&priv->lock);
	list_add(&gntdev_dmabuf->next, &priv->imp_list);
	mutex_unlock(&priv->lock);

	return gntdev_dmabuf;

fail_end_access:
	dmabuf_imp_end_foreign_access(gntdev_dmabuf->u.imp.refs, count);
fail_unmap:
	dma_buf_unmap_attachment(attach, sgt, DMA_BIDIRECTIONAL);
fail_detach:
	dma_buf_detach(dma_buf, attach);
fail_free_obj:
	dmabuf_imp_free_storage(gntdev_dmabuf);
fail_put:
	dma_buf_put(dma_buf);
	return ret;
}

/*
 * Find the hyper dma-buf by its file descriptor and remove
 * it from the buffer's list.
 */
static struct gntdev_dmabuf *
dmabuf_imp_find_unlink(struct gntdev_dmabuf_priv *priv, int fd)
{
	struct gntdev_dmabuf *q, *gntdev_dmabuf, *ret = ERR_PTR(-ENOENT);

	mutex_lock(&priv->lock);
	list_for_each_entry_safe(gntdev_dmabuf, q, &priv->imp_list, next) {
		if (gntdev_dmabuf->fd == fd) {
			pr_debug("Found gntdev_dmabuf in the import list\n");
			ret = gntdev_dmabuf;
			list_del(&gntdev_dmabuf->next);
			break;
		}
	}
	mutex_unlock(&priv->lock);
	return ret;
}

static int dmabuf_imp_release(struct gntdev_dmabuf_priv *priv, u32 fd)
{
	struct gntdev_dmabuf *gntdev_dmabuf;
	struct dma_buf_attachment *attach;
	struct dma_buf *dma_buf;

	gntdev_dmabuf = dmabuf_imp_find_unlink(priv, fd);
	if (IS_ERR(gntdev_dmabuf))
		return PTR_ERR(gntdev_dmabuf);

	pr_debug("Releasing DMA buffer with fd %d\n", fd);

	dmabuf_imp_end_foreign_access(gntdev_dmabuf->u.imp.refs,
				      gntdev_dmabuf->nr_pages);

	attach = gntdev_dmabuf->u.imp.attach;

	if (gntdev_dmabuf->u.imp.sgt)
		dma_buf_unmap_attachment(attach, gntdev_dmabuf->u.imp.sgt,
					 DMA_BIDIRECTIONAL);
	dma_buf = attach->dmabuf;
	dma_buf_detach(attach->dmabuf, attach);
	dma_buf_put(dma_buf);

	dmabuf_imp_free_storage(gntdev_dmabuf);
	return 0;
}

static void dmabuf_imp_release_all(struct gntdev_dmabuf_priv *priv)
{
	struct gntdev_dmabuf *q, *gntdev_dmabuf;

	list_for_each_entry_safe(gntdev_dmabuf, q, &priv->imp_list, next)
		dmabuf_imp_release(priv, gntdev_dmabuf->fd);
}

/* DMA buffer IOCTL support. */

long gntdev_ioctl_dmabuf_exp_from_refs(struct gntdev_priv *priv, int use_ptemod,
				       struct ioctl_gntdev_dmabuf_exp_from_refs __user *u)
{
	struct ioctl_gntdev_dmabuf_exp_from_refs op;
	u32 *refs;
	long ret;

	if (use_ptemod) {
		pr_debug("Cannot provide dma-buf: use_ptemode %d\n",
			 use_ptemod);
		return -EINVAL;
	}

	if (copy_from_user(&op, u, sizeof(op)) != 0)
		return -EFAULT;

	if (unlikely(gntdev_test_page_count(op.count)))
		return -EINVAL;

	refs = kcalloc(op.count, sizeof(*refs), GFP_KERNEL);
	if (!refs)
		return -ENOMEM;

	if (copy_from_user(refs, u->refs, sizeof(*refs) * op.count) != 0) {
		ret = -EFAULT;
		goto out;
	}

	ret = dmabuf_exp_from_refs(priv, op.flags, op.count,
				   op.domid, refs, &op.fd);
	if (ret)
		goto out;

	if (copy_to_user(u, &op, sizeof(op)) != 0)
		ret = -EFAULT;

out:
	kfree(refs);
	return ret;
}

long gntdev_ioctl_dmabuf_exp_wait_released(struct gntdev_priv *priv,
					   struct ioctl_gntdev_dmabuf_exp_wait_released __user *u)
{
	struct ioctl_gntdev_dmabuf_exp_wait_released op;

	if (copy_from_user(&op, u, sizeof(op)) != 0)
		return -EFAULT;

	return dmabuf_exp_wait_released(priv->dmabuf_priv, op.fd,
					op.wait_to_ms);
}

long gntdev_ioctl_dmabuf_imp_to_refs(struct gntdev_priv *priv,
				     struct ioctl_gntdev_dmabuf_imp_to_refs __user *u)
{
	struct ioctl_gntdev_dmabuf_imp_to_refs op;
	struct gntdev_dmabuf *gntdev_dmabuf;
	long ret;

	if (copy_from_user(&op, u, sizeof(op)) != 0)
		return -EFAULT;

	if (unlikely(gntdev_test_page_count(op.count)))
		return -EINVAL;

	gntdev_dmabuf = dmabuf_imp_to_refs(priv->dmabuf_priv,
					   priv->dma_dev, op.fd,
					   op.count, op.domid);
	if (IS_ERR(gntdev_dmabuf))
		return PTR_ERR(gntdev_dmabuf);

	if (copy_to_user(u->refs, gntdev_dmabuf->u.imp.refs,
			 sizeof(*u->refs) * op.count) != 0) {
		ret = -EFAULT;
		goto out_release;
	}
	return 0;

out_release:
	dmabuf_imp_release(priv->dmabuf_priv, op.fd);
	return ret;
}

long gntdev_ioctl_dmabuf_imp_release(struct gntdev_priv *priv,
				     struct ioctl_gntdev_dmabuf_imp_release __user *u)
{
	struct ioctl_gntdev_dmabuf_imp_release op;

	if (copy_from_user(&op, u, sizeof(op)) != 0)
		return -EFAULT;

	return dmabuf_imp_release(priv->dmabuf_priv, op.fd);
}

struct gntdev_dmabuf_priv *gntdev_dmabuf_init(struct file *filp)
{
	struct gntdev_dmabuf_priv *priv;

	priv = kzalloc(sizeof(*priv), GFP_KERNEL);
	if (!priv)
		return ERR_PTR(-ENOMEM);

	mutex_init(&priv->lock);
	INIT_LIST_HEAD(&priv->exp_list);
	INIT_LIST_HEAD(&priv->exp_wait_list);
	INIT_LIST_HEAD(&priv->imp_list);

	priv->filp = filp;

	return priv;
}

void gntdev_dmabuf_fini(struct gntdev_dmabuf_priv *priv)
{
	dmabuf_imp_release_all(priv);
	kfree(priv);
}