summaryrefslogtreecommitdiffstats
path: root/drivers/xen/grant-table.c
blob: 8c71ab80175653827d0ceb966b74b7aef73287d3 (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
/******************************************************************************
 * grant_table.c
 *
 * Granting foreign access to our memory reservation.
 *
 * Copyright (c) 2005-2006, Christopher Clark
 * Copyright (c) 2004-2005, K A Fraser
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License version 2
 * as published by the Free Software Foundation; or, when distributed
 * separately from the Linux kernel or incorporated into other
 * software packages, subject to the following license:
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this source file (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
 * 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.
 */

#include <linux/module.h>
#include <linux/sched.h>
#include <linux/mm.h>
#include <linux/slab.h>
#include <linux/vmalloc.h>
#include <linux/uaccess.h>
#include <linux/io.h>

#include <xen/xen.h>
#include <xen/interface/xen.h>
#include <xen/page.h>
#include <xen/grant_table.h>
#include <xen/interface/memory.h>
#include <asm/xen/hypercall.h>

#include <asm/pgtable.h>
#include <asm/sync_bitops.h>


/* External tools reserve first few grant table entries. */
#define NR_RESERVED_ENTRIES 8
#define GNTTAB_LIST_END 0xffffffff
#define GREFS_PER_GRANT_FRAME (PAGE_SIZE / sizeof(struct grant_entry))

static grant_ref_t **gnttab_list;
static unsigned int nr_grant_frames;
static unsigned int boot_max_nr_grant_frames;
static int gnttab_free_count;
static grant_ref_t gnttab_free_head;
static DEFINE_SPINLOCK(gnttab_list_lock);
unsigned long xen_hvm_resume_frames;
EXPORT_SYMBOL_GPL(xen_hvm_resume_frames);

static struct grant_entry *shared;

static struct gnttab_free_callback *gnttab_free_callback_list;

static int gnttab_expand(unsigned int req_entries);

#define RPP (PAGE_SIZE / sizeof(grant_ref_t))

static inline grant_ref_t *__gnttab_entry(grant_ref_t entry)
{
	return &gnttab_list[(entry) / RPP][(entry) % RPP];
}
/* This can be used as an l-value */
#define gnttab_entry(entry) (*__gnttab_entry(entry))

static int get_free_entries(unsigned count)
{
	unsigned long flags;
	int ref, rc = 0;
	grant_ref_t head;

	spin_lock_irqsave(&gnttab_list_lock, flags);

	if ((gnttab_free_count < count) &&
	    ((rc = gnttab_expand(count - gnttab_free_count)) < 0)) {
		spin_unlock_irqrestore(&gnttab_list_lock, flags);
		return rc;
	}

	ref = head = gnttab_free_head;
	gnttab_free_count -= count;
	while (count-- > 1)
		head = gnttab_entry(head);
	gnttab_free_head = gnttab_entry(head);
	gnttab_entry(head) = GNTTAB_LIST_END;

	spin_unlock_irqrestore(&gnttab_list_lock, flags);

	return ref;
}

static void do_free_callbacks(void)
{
	struct gnttab_free_callback *callback, *next;

	callback = gnttab_free_callback_list;
	gnttab_free_callback_list = NULL;

	while (callback != NULL) {
		next = callback->next;
		if (gnttab_free_count >= callback->count) {
			callback->next = NULL;
			callback->fn(callback->arg);
		} else {
			callback->next = gnttab_free_callback_list;
			gnttab_free_callback_list = callback;
		}
		callback = next;
	}
}

static inline void check_free_callbacks(void)
{
	if (unlikely(gnttab_free_callback_list))
		do_free_callbacks();
}

static void put_free_entry(grant_ref_t ref)
{
	unsigned long flags;
	spin_lock_irqsave(&gnttab_list_lock, flags);
	gnttab_entry(ref) = gnttab_free_head;
	gnttab_free_head = ref;
	gnttab_free_count++;
	check_free_callbacks();
	spin_unlock_irqrestore(&gnttab_list_lock, flags);
}

static void update_grant_entry(grant_ref_t ref, domid_t domid,
			       unsigned long frame, unsigned flags)
{
	/*
	 * Introducing a valid entry into the grant table:
	 *  1. Write ent->domid.
	 *  2. Write ent->frame:
	 *      GTF_permit_access:   Frame to which access is permitted.
	 *      GTF_accept_transfer: Pseudo-phys frame slot being filled by new
	 *                           frame, or zero if none.
	 *  3. Write memory barrier (WMB).
	 *  4. Write ent->flags, inc. valid type.
	 */
	shared[ref].frame = frame;
	shared[ref].domid = domid;
	wmb();
	shared[ref].flags = flags;
}

/*
 * Public grant-issuing interface functions
 */
void gnttab_grant_foreign_access_ref(grant_ref_t ref, domid_t domid,
				     unsigned long frame, int readonly)
{
	update_grant_entry(ref, domid, frame,
			   GTF_permit_access | (readonly ? GTF_readonly : 0));
}
EXPORT_SYMBOL_GPL(gnttab_grant_foreign_access_ref);

int gnttab_grant_foreign_access(domid_t domid, unsigned long frame,
				int readonly)
{
	int ref;

	ref = get_free_entries(1);
	if (unlikely(ref < 0))
		return -ENOSPC;

	gnttab_grant_foreign_access_ref(ref, domid, frame, readonly);

	return ref;
}
EXPORT_SYMBOL_GPL(gnttab_grant_foreign_access);

int gnttab_query_foreign_access(grant_ref_t ref)
{
	u16 nflags;

	nflags = shared[ref].flags;

	return (nflags & (GTF_reading|GTF_writing));
}
EXPORT_SYMBOL_GPL(gnttab_query_foreign_access);

int gnttab_end_foreign_access_ref(grant_ref_t ref, int readonly)
{
	u16 flags, nflags;

	nflags = shared[ref].flags;
	do {
		flags = nflags;
		if (flags & (GTF_reading|GTF_writing)) {
			printk(KERN_ALERT "WARNING: g.e. still in use!\n");
			return 0;
		}
	} while ((nflags = sync_cmpxchg(&shared[ref].flags, flags, 0)) != flags);

	return 1;
}
EXPORT_SYMBOL_GPL(gnttab_end_foreign_access_ref);

void gnttab_end_foreign_access(grant_ref_t ref, int readonly,
			       unsigned long page)
{
	if (gnttab_end_foreign_access_ref(ref, readonly)) {
		put_free_entry(ref);
		if (page != 0)
			free_page(page);
	} else {
		/* XXX This needs to be fixed so that the ref and page are
		   placed on a list to be freed up later. */
		printk(KERN_WARNING
		       "WARNING: leaking g.e. and page still in use!\n");
	}
}
EXPORT_SYMBOL_GPL(gnttab_end_foreign_access);

int gnttab_grant_foreign_transfer(domid_t domid, unsigned long pfn)
{
	int ref;

	ref = get_free_entries(1);
	if (unlikely(ref < 0))
		return -ENOSPC;
	gnttab_grant_foreign_transfer_ref(ref, domid, pfn);

	return ref;
}
EXPORT_SYMBOL_GPL(gnttab_grant_foreign_transfer);

void gnttab_grant_foreign_transfer_ref(grant_ref_t ref, domid_t domid,
				       unsigned long pfn)
{
	update_grant_entry(ref, domid, pfn, GTF_accept_transfer);
}
EXPORT_SYMBOL_GPL(gnttab_grant_foreign_transfer_ref);

unsigned long gnttab_end_foreign_transfer_ref(grant_ref_t ref)
{
	unsigned long frame;
	u16           flags;

	/*
	 * If a transfer is not even yet started, try to reclaim the grant
	 * reference and return failure (== 0).
	 */
	while (!((flags = shared[ref].flags) & GTF_transfer_committed)) {
		if (sync_cmpxchg(&shared[ref].flags, flags, 0) == flags)
			return 0;
		cpu_relax();
	}

	/* If a transfer is in progress then wait until it is completed. */
	while (!(flags & GTF_transfer_completed)) {
		flags = shared[ref].flags;
		cpu_relax();
	}

	rmb();	/* Read the frame number /after/ reading completion status. */
	frame = shared[ref].frame;
	BUG_ON(frame == 0);

	return frame;
}
EXPORT_SYMBOL_GPL(gnttab_end_foreign_transfer_ref);

unsigned long gnttab_end_foreign_transfer(grant_ref_t ref)
{
	unsigned long frame = gnttab_end_foreign_transfer_ref(ref);
	put_free_entry(ref);
	return frame;
}
EXPORT_SYMBOL_GPL(gnttab_end_foreign_transfer);

void gnttab_free_grant_reference(grant_ref_t ref)
{
	put_free_entry(ref);
}
EXPORT_SYMBOL_GPL(gnttab_free_grant_reference);

void gnttab_free_grant_references(grant_ref_t head)
{
	grant_ref_t ref;
	unsigned long flags;
	int count = 1;
	if (head == GNTTAB_LIST_END)
		return;
	spin_lock_irqsave(&gnttab_list_lock, flags);
	ref = head;
	while (gnttab_entry(ref) != GNTTAB_LIST_END) {
		ref = gnttab_entry(ref);
		count++;
	}
	gnttab_entry(ref) = gnttab_free_head;
	gnttab_free_head = head;
	gnttab_free_count += count;
	check_free_callbacks();
	spin_unlock_irqrestore(&gnttab_list_lock, flags);
}
EXPORT_SYMBOL_GPL(gnttab_free_grant_references);

int gnttab_alloc_grant_references(u16 count, grant_ref_t *head)
{
	int h = get_free_entries(count);

	if (h < 0)
		return -ENOSPC;

	*head = h;

	return 0;
}
EXPORT_SYMBOL_GPL(gnttab_alloc_grant_references);

int gnttab_empty_grant_references(const grant_ref_t *private_head)
{
	return (*private_head == GNTTAB_LIST_END);
}
EXPORT_SYMBOL_GPL(gnttab_empty_grant_references);

int gnttab_claim_grant_reference(grant_ref_t *private_head)
{
	grant_ref_t g = *private_head;
	if (unlikely(g == GNTTAB_LIST_END))
		return -ENOSPC;
	*private_head = gnttab_entry(g);
	return g;
}
EXPORT_SYMBOL_GPL(gnttab_claim_grant_reference);

void gnttab_release_grant_reference(grant_ref_t *private_head,
				    grant_ref_t release)
{
	gnttab_entry(release) = *private_head;
	*private_head = release;
}
EXPORT_SYMBOL_GPL(gnttab_release_grant_reference);

void gnttab_request_free_callback(struct gnttab_free_callback *callback,
				  void (*fn)(void *), void *arg, u16 count)
{
	unsigned long flags;
	spin_lock_irqsave(&gnttab_list_lock, flags);
	if (callback->next)
		goto out;
	callback->fn = fn;
	callback->arg = arg;
	callback->count = count;
	callback->next = gnttab_free_callback_list;
	gnttab_free_callback_list = callback;
	check_free_callbacks();
out:
	spin_unlock_irqrestore(&gnttab_list_lock, flags);
}
EXPORT_SYMBOL_GPL(gnttab_request_free_callback);

void gnttab_cancel_free_callback(struct gnttab_free_callback *callback)
{
	struct gnttab_free_callback **pcb;
	unsigned long flags;

	spin_lock_irqsave(&gnttab_list_lock, flags);
	for (pcb = &gnttab_free_callback_list; *pcb; pcb = &(*pcb)->next) {
		if (*pcb == callback) {
			*pcb = callback->next;
			break;
		}
	}
	spin_unlock_irqrestore(&gnttab_list_lock, flags);
}
EXPORT_SYMBOL_GPL(gnttab_cancel_free_callback);

static int grow_gnttab_list(unsigned int more_frames)
{
	unsigned int new_nr_grant_frames, extra_entries, i;
	unsigned int nr_glist_frames, new_nr_glist_frames;

	new_nr_grant_frames = nr_grant_frames + more_frames;
	extra_entries       = more_frames * GREFS_PER_GRANT_FRAME;

	nr_glist_frames = (nr_grant_frames * GREFS_PER_GRANT_FRAME + RPP - 1) / RPP;
	new_nr_glist_frames =
		(new_nr_grant_frames * GREFS_PER_GRANT_FRAME + RPP - 1) / RPP;
	for (i = nr_glist_frames; i < new_nr_glist_frames; i++) {
		gnttab_list[i] = (grant_ref_t *)__get_free_page(GFP_ATOMIC);
		if (!gnttab_list[i])
			goto grow_nomem;
	}


	for (i = GREFS_PER_GRANT_FRAME * nr_grant_frames;
	     i < GREFS_PER_GRANT_FRAME * new_nr_grant_frames - 1; i++)
		gnttab_entry(i) = i + 1;

	gnttab_entry(i) = gnttab_free_head;
	gnttab_free_head = GREFS_PER_GRANT_FRAME * nr_grant_frames;
	gnttab_free_count += extra_entries;

	nr_grant_frames = new_nr_grant_frames;

	check_free_callbacks();

	return 0;

grow_nomem:
	for ( ; i >= nr_glist_frames; i--)
		free_page((unsigned long) gnttab_list[i]);
	return -ENOMEM;
}

static unsigned int __max_nr_grant_frames(void)
{
	struct gnttab_query_size query;
	int rc;

	query.dom = DOMID_SELF;

	rc = HYPERVISOR_grant_table_op(GNTTABOP_query_size, &query, 1);
	if ((rc < 0) || (query.status != GNTST_okay))
		return 4; /* Legacy max supported number of frames */

	return query.max_nr_frames;
}

unsigned int gnttab_max_grant_frames(void)
{
	unsigned int xen_max = __max_nr_grant_frames();

	if (xen_max > boot_max_nr_grant_frames)
		return boot_max_nr_grant_frames;
	return xen_max;
}
EXPORT_SYMBOL_GPL(gnttab_max_grant_frames);

int gnttab_map_refs(struct gnttab_map_grant_ref *map_ops,
			struct gnttab_map_grant_ref *kmap_ops,
			struct page **pages, unsigned int count)
{
	int i, ret;
	pte_t *pte;
	unsigned long mfn;

	ret = HYPERVISOR_grant_table_op(GNTTABOP_map_grant_ref, map_ops, count);
	if (ret)
		return ret;

	if (xen_feature(XENFEAT_auto_translated_physmap))
		return ret;

	for (i = 0; i < count; i++) {
		/* Do not add to override if the map failed. */
		if (map_ops[i].status)
			continue;

		if (map_ops[i].flags & GNTMAP_contains_pte) {
			pte = (pte_t *) (mfn_to_virt(PFN_DOWN(map_ops[i].host_addr)) +
				(map_ops[i].host_addr & ~PAGE_MASK));
			mfn = pte_mfn(*pte);
		} else {
			/* If you really wanted to do this:
			 * mfn = PFN_DOWN(map_ops[i].dev_bus_addr);
			 *
			 * The reason we do not implement it is b/c on the
			 * unmap path (gnttab_unmap_refs) we have no means of
			 * checking whether the page is !GNTMAP_contains_pte.
			 *
			 * That is without some extra data-structure to carry
			 * the struct page, bool clear_pte, and list_head next
			 * tuples and deal with allocation/delallocation, etc.
			 *
			 * The users of this API set the GNTMAP_contains_pte
			 * flag so lets just return not supported until it
			 * becomes neccessary to implement.
			 */
			return -EOPNOTSUPP;
		}
		ret = m2p_add_override(mfn, pages[i], &kmap_ops[i]);
		if (ret)
			return ret;
	}

	return ret;
}
EXPORT_SYMBOL_GPL(gnttab_map_refs);

int gnttab_unmap_refs(struct gnttab_unmap_grant_ref *unmap_ops,
		struct page **pages, unsigned int count)
{
	int i, ret;

	ret = HYPERVISOR_grant_table_op(GNTTABOP_unmap_grant_ref, unmap_ops, count);
	if (ret)
		return ret;

	if (xen_feature(XENFEAT_auto_translated_physmap))
		return ret;

	for (i = 0; i < count; i++) {
		ret = m2p_remove_override(pages[i], true /* clear the PTE */);
		if (ret)
			return ret;
	}

	return ret;
}
EXPORT_SYMBOL_GPL(gnttab_unmap_refs);

static int gnttab_map(unsigned int start_idx, unsigned int end_idx)
{
	struct gnttab_setup_table setup;
	unsigned long *frames;
	unsigned int nr_gframes = end_idx + 1;
	int rc;

	if (xen_hvm_domain()) {
		struct xen_add_to_physmap xatp;
		unsigned int i = end_idx;
		rc = 0;
		/*
		 * Loop backwards, so that the first hypercall has the largest
		 * index, ensuring that the table will grow only once.
		 */
		do {
			xatp.domid = DOMID_SELF;
			xatp.idx = i;
			xatp.space = XENMAPSPACE_grant_table;
			xatp.gpfn = (xen_hvm_resume_frames >> PAGE_SHIFT) + i;
			rc = HYPERVISOR_memory_op(XENMEM_add_to_physmap, &xatp);
			if (rc != 0) {
				printk(KERN_WARNING
						"grant table add_to_physmap failed, err=%d\n", rc);
				break;
			}
		} while (i-- > start_idx);

		return rc;
	}

	frames = kmalloc(nr_gframes * sizeof(unsigned long), GFP_ATOMIC);
	if (!frames)
		return -ENOMEM;

	setup.dom        = DOMID_SELF;
	setup.nr_frames  = nr_gframes;
	set_xen_guest_handle(setup.frame_list, frames);

	rc = HYPERVISOR_grant_table_op(GNTTABOP_setup_table, &setup, 1);
	if (rc == -ENOSYS) {
		kfree(frames);
		return -ENOSYS;
	}

	BUG_ON(rc || setup.status);

	rc = arch_gnttab_map_shared(frames, nr_gframes, gnttab_max_grant_frames(),
				    &shared);
	BUG_ON(rc);

	kfree(frames);

	return 0;
}

int gnttab_resume(void)
{
	unsigned int max_nr_gframes;

	max_nr_gframes = gnttab_max_grant_frames();
	if (max_nr_gframes < nr_grant_frames)
		return -ENOSYS;

	if (xen_pv_domain())
		return gnttab_map(0, nr_grant_frames - 1);

	if (!shared) {
		shared = ioremap(xen_hvm_resume_frames, PAGE_SIZE * max_nr_gframes);
		if (shared == NULL) {
			printk(KERN_WARNING
					"Failed to ioremap gnttab share frames!");
			return -ENOMEM;
		}
	}

	gnttab_map(0, nr_grant_frames - 1);

	return 0;
}

int gnttab_suspend(void)
{
	arch_gnttab_unmap_shared(shared, nr_grant_frames);
	return 0;
}

static int gnttab_expand(unsigned int req_entries)
{
	int rc;
	unsigned int cur, extra;

	cur = nr_grant_frames;
	extra = ((req_entries + (GREFS_PER_GRANT_FRAME-1)) /
		 GREFS_PER_GRANT_FRAME);
	if (cur + extra > gnttab_max_grant_frames())
		return -ENOSPC;

	rc = gnttab_map(cur, cur + extra - 1);
	if (rc == 0)
		rc = grow_gnttab_list(extra);

	return rc;
}

int gnttab_init(void)
{
	int i;
	unsigned int max_nr_glist_frames, nr_glist_frames;
	unsigned int nr_init_grefs;

	nr_grant_frames = 1;
	boot_max_nr_grant_frames = __max_nr_grant_frames();

	/* Determine the maximum number of frames required for the
	 * grant reference free list on the current hypervisor.
	 */
	max_nr_glist_frames = (boot_max_nr_grant_frames *
			       GREFS_PER_GRANT_FRAME / RPP);

	gnttab_list = kmalloc(max_nr_glist_frames * sizeof(grant_ref_t *),
			      GFP_KERNEL);
	if (gnttab_list == NULL)
		return -ENOMEM;

	nr_glist_frames = (nr_grant_frames * GREFS_PER_GRANT_FRAME + RPP - 1) / RPP;
	for (i = 0; i < nr_glist_frames; i++) {
		gnttab_list[i] = (grant_ref_t *)__get_free_page(GFP_KERNEL);
		if (gnttab_list[i] == NULL)
			goto ini_nomem;
	}

	if (gnttab_resume() < 0)
		return -ENODEV;

	nr_init_grefs = nr_grant_frames * GREFS_PER_GRANT_FRAME;

	for (i = NR_RESERVED_ENTRIES; i < nr_init_grefs - 1; i++)
		gnttab_entry(i) = i + 1;

	gnttab_entry(nr_init_grefs - 1) = GNTTAB_LIST_END;
	gnttab_free_count = nr_init_grefs - NR_RESERVED_ENTRIES;
	gnttab_free_head  = NR_RESERVED_ENTRIES;

	printk("Grant table initialized\n");
	return 0;

 ini_nomem:
	for (i--; i >= 0; i--)
		free_page((unsigned long)gnttab_list[i]);
	kfree(gnttab_list);
	return -ENOMEM;
}
EXPORT_SYMBOL_GPL(gnttab_init);

static int __devinit __gnttab_init(void)
{
	/* Delay grant-table initialization in the PV on HVM case */
	if (xen_hvm_domain())
		return 0;

	if (!xen_pv_domain())
		return -ENODEV;

	return gnttab_init();
}

core_initcall(__gnttab_init);
OpenPOWER on IntegriCloud