xref: /openbmc/linux/drivers/xen/grant-table.c (revision 565d76cb) 
1 /******************************************************************************
2  * grant_table.c
3  *
4  * Granting foreign access to our memory reservation.
5  *
6  * Copyright (c) 2005-2006, Christopher Clark
7  * Copyright (c) 2004-2005, K A Fraser
8  *
9  * This program is free software; you can redistribute it and/or
10  * modify it under the terms of the GNU General Public License version 2
11  * as published by the Free Software Foundation; or, when distributed
12  * separately from the Linux kernel or incorporated into other
13  * software packages, subject to the following license:
14  *
15  * Permission is hereby granted, free of charge, to any person obtaining a copy
16  * of this source file (the "Software"), to deal in the Software without
17  * restriction, including without limitation the rights to use, copy, modify,
18  * merge, publish, distribute, sublicense, and/or sell copies of the Software,
19  * and to permit persons to whom the Software is furnished to do so, subject to
20  * the following conditions:
21  *
22  * The above copyright notice and this permission notice shall be included in
23  * all copies or substantial portions of the Software.
24  *
25  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
26  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
27  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
28  * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
29  * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
30  * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
31  * IN THE SOFTWARE.
32  */
33 
34 #include <linux/module.h>
35 #include <linux/sched.h>
36 #include <linux/mm.h>
37 #include <linux/slab.h>
38 #include <linux/vmalloc.h>
39 #include <linux/uaccess.h>
40 #include <linux/io.h>
41 
42 #include <xen/xen.h>
43 #include <xen/interface/xen.h>
44 #include <xen/page.h>
45 #include <xen/grant_table.h>
46 #include <xen/interface/memory.h>
47 #include <asm/xen/hypercall.h>
48 
49 #include <asm/pgtable.h>
50 #include <asm/sync_bitops.h>
51 
52 
53 /* External tools reserve first few grant table entries. */
54 #define NR_RESERVED_ENTRIES 8
55 #define GNTTAB_LIST_END 0xffffffff
56 #define GREFS_PER_GRANT_FRAME (PAGE_SIZE / sizeof(struct grant_entry))
57 
58 static grant_ref_t **gnttab_list;
59 static unsigned int nr_grant_frames;
60 static unsigned int boot_max_nr_grant_frames;
61 static int gnttab_free_count;
62 static grant_ref_t gnttab_free_head;
63 static DEFINE_SPINLOCK(gnttab_list_lock);
64 unsigned long xen_hvm_resume_frames;
65 EXPORT_SYMBOL_GPL(xen_hvm_resume_frames);
66 
67 static struct grant_entry *shared;
68 
69 static struct gnttab_free_callback *gnttab_free_callback_list;
70 
71 static int gnttab_expand(unsigned int req_entries);
72 
73 #define RPP (PAGE_SIZE / sizeof(grant_ref_t))
74 
75 static inline grant_ref_t *__gnttab_entry(grant_ref_t entry)
76 {
77 	return &gnttab_list[(entry) / RPP][(entry) % RPP];
78 }
79 /* This can be used as an l-value */
80 #define gnttab_entry(entry) (*__gnttab_entry(entry))
81 
82 static int get_free_entries(unsigned count)
83 {
84 	unsigned long flags;
85 	int ref, rc;
86 	grant_ref_t head;
87 
88 	spin_lock_irqsave(&gnttab_list_lock, flags);
89 
90 	if ((gnttab_free_count < count) &&
91 	    ((rc = gnttab_expand(count - gnttab_free_count)) < 0)) {
92 		spin_unlock_irqrestore(&gnttab_list_lock, flags);
93 		return rc;
94 	}
95 
96 	ref = head = gnttab_free_head;
97 	gnttab_free_count -= count;
98 	while (count-- > 1)
99 		head = gnttab_entry(head);
100 	gnttab_free_head = gnttab_entry(head);
101 	gnttab_entry(head) = GNTTAB_LIST_END;
102 
103 	spin_unlock_irqrestore(&gnttab_list_lock, flags);
104 
105 	return ref;
106 }
107 
108 static void do_free_callbacks(void)
109 {
110 	struct gnttab_free_callback *callback, *next;
111 
112 	callback = gnttab_free_callback_list;
113 	gnttab_free_callback_list = NULL;
114 
115 	while (callback != NULL) {
116 		next = callback->next;
117 		if (gnttab_free_count >= callback->count) {
118 			callback->next = NULL;
119 			callback->fn(callback->arg);
120 		} else {
121 			callback->next = gnttab_free_callback_list;
122 			gnttab_free_callback_list = callback;
123 		}
124 		callback = next;
125 	}
126 }
127 
128 static inline void check_free_callbacks(void)
129 {
130 	if (unlikely(gnttab_free_callback_list))
131 		do_free_callbacks();
132 }
133 
134 static void put_free_entry(grant_ref_t ref)
135 {
136 	unsigned long flags;
137 	spin_lock_irqsave(&gnttab_list_lock, flags);
138 	gnttab_entry(ref) = gnttab_free_head;
139 	gnttab_free_head = ref;
140 	gnttab_free_count++;
141 	check_free_callbacks();
142 	spin_unlock_irqrestore(&gnttab_list_lock, flags);
143 }
144 
145 static void update_grant_entry(grant_ref_t ref, domid_t domid,
146 			       unsigned long frame, unsigned flags)
147 {
148 	/*
149 	 * Introducing a valid entry into the grant table:
150 	 *  1. Write ent->domid.
151 	 *  2. Write ent->frame:
152 	 *      GTF_permit_access:   Frame to which access is permitted.
153 	 *      GTF_accept_transfer: Pseudo-phys frame slot being filled by new
154 	 *                           frame, or zero if none.
155 	 *  3. Write memory barrier (WMB).
156 	 *  4. Write ent->flags, inc. valid type.
157 	 */
158 	shared[ref].frame = frame;
159 	shared[ref].domid = domid;
160 	wmb();
161 	shared[ref].flags = flags;
162 }
163 
164 /*
165  * Public grant-issuing interface functions
166  */
167 void gnttab_grant_foreign_access_ref(grant_ref_t ref, domid_t domid,
168 				     unsigned long frame, int readonly)
169 {
170 	update_grant_entry(ref, domid, frame,
171 			   GTF_permit_access | (readonly ? GTF_readonly : 0));
172 }
173 EXPORT_SYMBOL_GPL(gnttab_grant_foreign_access_ref);
174 
175 int gnttab_grant_foreign_access(domid_t domid, unsigned long frame,
176 				int readonly)
177 {
178 	int ref;
179 
180 	ref = get_free_entries(1);
181 	if (unlikely(ref < 0))
182 		return -ENOSPC;
183 
184 	gnttab_grant_foreign_access_ref(ref, domid, frame, readonly);
185 
186 	return ref;
187 }
188 EXPORT_SYMBOL_GPL(gnttab_grant_foreign_access);
189 
190 int gnttab_query_foreign_access(grant_ref_t ref)
191 {
192 	u16 nflags;
193 
194 	nflags = shared[ref].flags;
195 
196 	return (nflags & (GTF_reading|GTF_writing));
197 }
198 EXPORT_SYMBOL_GPL(gnttab_query_foreign_access);
199 
200 int gnttab_end_foreign_access_ref(grant_ref_t ref, int readonly)
201 {
202 	u16 flags, nflags;
203 
204 	nflags = shared[ref].flags;
205 	do {
206 		flags = nflags;
207 		if (flags & (GTF_reading|GTF_writing)) {
208 			printk(KERN_ALERT "WARNING: g.e. still in use!\n");
209 			return 0;
210 		}
211 	} while ((nflags = sync_cmpxchg(&shared[ref].flags, flags, 0)) != flags);
212 
213 	return 1;
214 }
215 EXPORT_SYMBOL_GPL(gnttab_end_foreign_access_ref);
216 
217 void gnttab_end_foreign_access(grant_ref_t ref, int readonly,
218 			       unsigned long page)
219 {
220 	if (gnttab_end_foreign_access_ref(ref, readonly)) {
221 		put_free_entry(ref);
222 		if (page != 0)
223 			free_page(page);
224 	} else {
225 		/* XXX This needs to be fixed so that the ref and page are
226 		   placed on a list to be freed up later. */
227 		printk(KERN_WARNING
228 		       "WARNING: leaking g.e. and page still in use!\n");
229 	}
230 }
231 EXPORT_SYMBOL_GPL(gnttab_end_foreign_access);
232 
233 int gnttab_grant_foreign_transfer(domid_t domid, unsigned long pfn)
234 {
235 	int ref;
236 
237 	ref = get_free_entries(1);
238 	if (unlikely(ref < 0))
239 		return -ENOSPC;
240 	gnttab_grant_foreign_transfer_ref(ref, domid, pfn);
241 
242 	return ref;
243 }
244 EXPORT_SYMBOL_GPL(gnttab_grant_foreign_transfer);
245 
246 void gnttab_grant_foreign_transfer_ref(grant_ref_t ref, domid_t domid,
247 				       unsigned long pfn)
248 {
249 	update_grant_entry(ref, domid, pfn, GTF_accept_transfer);
250 }
251 EXPORT_SYMBOL_GPL(gnttab_grant_foreign_transfer_ref);
252 
253 unsigned long gnttab_end_foreign_transfer_ref(grant_ref_t ref)
254 {
255 	unsigned long frame;
256 	u16           flags;
257 
258 	/*
259 	 * If a transfer is not even yet started, try to reclaim the grant
260 	 * reference and return failure (== 0).
261 	 */
262 	while (!((flags = shared[ref].flags) & GTF_transfer_committed)) {
263 		if (sync_cmpxchg(&shared[ref].flags, flags, 0) == flags)
264 			return 0;
265 		cpu_relax();
266 	}
267 
268 	/* If a transfer is in progress then wait until it is completed. */
269 	while (!(flags & GTF_transfer_completed)) {
270 		flags = shared[ref].flags;
271 		cpu_relax();
272 	}
273 
274 	rmb();	/* Read the frame number /after/ reading completion status. */
275 	frame = shared[ref].frame;
276 	BUG_ON(frame == 0);
277 
278 	return frame;
279 }
280 EXPORT_SYMBOL_GPL(gnttab_end_foreign_transfer_ref);
281 
282 unsigned long gnttab_end_foreign_transfer(grant_ref_t ref)
283 {
284 	unsigned long frame = gnttab_end_foreign_transfer_ref(ref);
285 	put_free_entry(ref);
286 	return frame;
287 }
288 EXPORT_SYMBOL_GPL(gnttab_end_foreign_transfer);
289 
290 void gnttab_free_grant_reference(grant_ref_t ref)
291 {
292 	put_free_entry(ref);
293 }
294 EXPORT_SYMBOL_GPL(gnttab_free_grant_reference);
295 
296 void gnttab_free_grant_references(grant_ref_t head)
297 {
298 	grant_ref_t ref;
299 	unsigned long flags;
300 	int count = 1;
301 	if (head == GNTTAB_LIST_END)
302 		return;
303 	spin_lock_irqsave(&gnttab_list_lock, flags);
304 	ref = head;
305 	while (gnttab_entry(ref) != GNTTAB_LIST_END) {
306 		ref = gnttab_entry(ref);
307 		count++;
308 	}
309 	gnttab_entry(ref) = gnttab_free_head;
310 	gnttab_free_head = head;
311 	gnttab_free_count += count;
312 	check_free_callbacks();
313 	spin_unlock_irqrestore(&gnttab_list_lock, flags);
314 }
315 EXPORT_SYMBOL_GPL(gnttab_free_grant_references);
316 
317 int gnttab_alloc_grant_references(u16 count, grant_ref_t *head)
318 {
319 	int h = get_free_entries(count);
320 
321 	if (h < 0)
322 		return -ENOSPC;
323 
324 	*head = h;
325 
326 	return 0;
327 }
328 EXPORT_SYMBOL_GPL(gnttab_alloc_grant_references);
329 
330 int gnttab_empty_grant_references(const grant_ref_t *private_head)
331 {
332 	return (*private_head == GNTTAB_LIST_END);
333 }
334 EXPORT_SYMBOL_GPL(gnttab_empty_grant_references);
335 
336 int gnttab_claim_grant_reference(grant_ref_t *private_head)
337 {
338 	grant_ref_t g = *private_head;
339 	if (unlikely(g == GNTTAB_LIST_END))
340 		return -ENOSPC;
341 	*private_head = gnttab_entry(g);
342 	return g;
343 }
344 EXPORT_SYMBOL_GPL(gnttab_claim_grant_reference);
345 
346 void gnttab_release_grant_reference(grant_ref_t *private_head,
347 				    grant_ref_t release)
348 {
349 	gnttab_entry(release) = *private_head;
350 	*private_head = release;
351 }
352 EXPORT_SYMBOL_GPL(gnttab_release_grant_reference);
353 
354 void gnttab_request_free_callback(struct gnttab_free_callback *callback,
355 				  void (*fn)(void *), void *arg, u16 count)
356 {
357 	unsigned long flags;
358 	spin_lock_irqsave(&gnttab_list_lock, flags);
359 	if (callback->next)
360 		goto out;
361 	callback->fn = fn;
362 	callback->arg = arg;
363 	callback->count = count;
364 	callback->next = gnttab_free_callback_list;
365 	gnttab_free_callback_list = callback;
366 	check_free_callbacks();
367 out:
368 	spin_unlock_irqrestore(&gnttab_list_lock, flags);
369 }
370 EXPORT_SYMBOL_GPL(gnttab_request_free_callback);
371 
372 void gnttab_cancel_free_callback(struct gnttab_free_callback *callback)
373 {
374 	struct gnttab_free_callback **pcb;
375 	unsigned long flags;
376 
377 	spin_lock_irqsave(&gnttab_list_lock, flags);
378 	for (pcb = &gnttab_free_callback_list; *pcb; pcb = &(*pcb)->next) {
379 		if (*pcb == callback) {
380 			*pcb = callback->next;
381 			break;
382 		}
383 	}
384 	spin_unlock_irqrestore(&gnttab_list_lock, flags);
385 }
386 EXPORT_SYMBOL_GPL(gnttab_cancel_free_callback);
387 
388 static int grow_gnttab_list(unsigned int more_frames)
389 {
390 	unsigned int new_nr_grant_frames, extra_entries, i;
391 	unsigned int nr_glist_frames, new_nr_glist_frames;
392 
393 	new_nr_grant_frames = nr_grant_frames + more_frames;
394 	extra_entries       = more_frames * GREFS_PER_GRANT_FRAME;
395 
396 	nr_glist_frames = (nr_grant_frames * GREFS_PER_GRANT_FRAME + RPP - 1) / RPP;
397 	new_nr_glist_frames =
398 		(new_nr_grant_frames * GREFS_PER_GRANT_FRAME + RPP - 1) / RPP;
399 	for (i = nr_glist_frames; i < new_nr_glist_frames; i++) {
400 		gnttab_list[i] = (grant_ref_t *)__get_free_page(GFP_ATOMIC);
401 		if (!gnttab_list[i])
402 			goto grow_nomem;
403 	}
404 
405 
406 	for (i = GREFS_PER_GRANT_FRAME * nr_grant_frames;
407 	     i < GREFS_PER_GRANT_FRAME * new_nr_grant_frames - 1; i++)
408 		gnttab_entry(i) = i + 1;
409 
410 	gnttab_entry(i) = gnttab_free_head;
411 	gnttab_free_head = GREFS_PER_GRANT_FRAME * nr_grant_frames;
412 	gnttab_free_count += extra_entries;
413 
414 	nr_grant_frames = new_nr_grant_frames;
415 
416 	check_free_callbacks();
417 
418 	return 0;
419 
420 grow_nomem:
421 	for ( ; i >= nr_glist_frames; i--)
422 		free_page((unsigned long) gnttab_list[i]);
423 	return -ENOMEM;
424 }
425 
426 static unsigned int __max_nr_grant_frames(void)
427 {
428 	struct gnttab_query_size query;
429 	int rc;
430 
431 	query.dom = DOMID_SELF;
432 
433 	rc = HYPERVISOR_grant_table_op(GNTTABOP_query_size, &query, 1);
434 	if ((rc < 0) || (query.status != GNTST_okay))
435 		return 4; /* Legacy max supported number of frames */
436 
437 	return query.max_nr_frames;
438 }
439 
440 unsigned int gnttab_max_grant_frames(void)
441 {
442 	unsigned int xen_max = __max_nr_grant_frames();
443 
444 	if (xen_max > boot_max_nr_grant_frames)
445 		return boot_max_nr_grant_frames;
446 	return xen_max;
447 }
448 EXPORT_SYMBOL_GPL(gnttab_max_grant_frames);
449 
450 int gnttab_map_refs(struct gnttab_map_grant_ref *map_ops,
451 		    struct page **pages, unsigned int count)
452 {
453 	int i, ret;
454 	pte_t *pte;
455 	unsigned long mfn;
456 
457 	ret = HYPERVISOR_grant_table_op(GNTTABOP_map_grant_ref, map_ops, count);
458 	if (ret)
459 		return ret;
460 
461 	if (xen_feature(XENFEAT_auto_translated_physmap))
462 		return ret;
463 
464 	for (i = 0; i < count; i++) {
465 		/* Do not add to override if the map failed. */
466 		if (map_ops[i].status)
467 			continue;
468 
469 		/* m2p override only supported for GNTMAP_contains_pte mappings */
470 		if (!(map_ops[i].flags & GNTMAP_contains_pte))
471 			continue;
472 		pte = (pte_t *) (mfn_to_virt(PFN_DOWN(map_ops[i].host_addr)) +
473 				(map_ops[i].host_addr & ~PAGE_MASK));
474 		mfn = pte_mfn(*pte);
475 		ret = m2p_add_override(mfn, pages[i]);
476 		if (ret)
477 			return ret;
478 	}
479 
480 	return ret;
481 }
482 EXPORT_SYMBOL_GPL(gnttab_map_refs);
483 
484 int gnttab_unmap_refs(struct gnttab_unmap_grant_ref *unmap_ops,
485 		struct page **pages, unsigned int count)
486 {
487 	int i, ret;
488 
489 	ret = HYPERVISOR_grant_table_op(GNTTABOP_unmap_grant_ref, unmap_ops, count);
490 	if (ret)
491 		return ret;
492 
493 	if (xen_feature(XENFEAT_auto_translated_physmap))
494 		return ret;
495 
496 	for (i = 0; i < count; i++) {
497 		ret = m2p_remove_override(pages[i]);
498 		if (ret)
499 			return ret;
500 	}
501 
502 	return ret;
503 }
504 EXPORT_SYMBOL_GPL(gnttab_unmap_refs);
505 
506 static int gnttab_map(unsigned int start_idx, unsigned int end_idx)
507 {
508 	struct gnttab_setup_table setup;
509 	unsigned long *frames;
510 	unsigned int nr_gframes = end_idx + 1;
511 	int rc;
512 
513 	if (xen_hvm_domain()) {
514 		struct xen_add_to_physmap xatp;
515 		unsigned int i = end_idx;
516 		rc = 0;
517 		/*
518 		 * Loop backwards, so that the first hypercall has the largest
519 		 * index, ensuring that the table will grow only once.
520 		 */
521 		do {
522 			xatp.domid = DOMID_SELF;
523 			xatp.idx = i;
524 			xatp.space = XENMAPSPACE_grant_table;
525 			xatp.gpfn = (xen_hvm_resume_frames >> PAGE_SHIFT) + i;
526 			rc = HYPERVISOR_memory_op(XENMEM_add_to_physmap, &xatp);
527 			if (rc != 0) {
528 				printk(KERN_WARNING
529 						"grant table add_to_physmap failed, err=%d\n", rc);
530 				break;
531 			}
532 		} while (i-- > start_idx);
533 
534 		return rc;
535 	}
536 
537 	frames = kmalloc(nr_gframes * sizeof(unsigned long), GFP_ATOMIC);
538 	if (!frames)
539 		return -ENOMEM;
540 
541 	setup.dom        = DOMID_SELF;
542 	setup.nr_frames  = nr_gframes;
543 	set_xen_guest_handle(setup.frame_list, frames);
544 
545 	rc = HYPERVISOR_grant_table_op(GNTTABOP_setup_table, &setup, 1);
546 	if (rc == -ENOSYS) {
547 		kfree(frames);
548 		return -ENOSYS;
549 	}
550 
551 	BUG_ON(rc || setup.status);
552 
553 	rc = arch_gnttab_map_shared(frames, nr_gframes, gnttab_max_grant_frames(),
554 				    &shared);
555 	BUG_ON(rc);
556 
557 	kfree(frames);
558 
559 	return 0;
560 }
561 
562 int gnttab_resume(void)
563 {
564 	unsigned int max_nr_gframes;
565 
566 	max_nr_gframes = gnttab_max_grant_frames();
567 	if (max_nr_gframes < nr_grant_frames)
568 		return -ENOSYS;
569 
570 	if (xen_pv_domain())
571 		return gnttab_map(0, nr_grant_frames - 1);
572 
573 	if (!shared) {
574 		shared = ioremap(xen_hvm_resume_frames, PAGE_SIZE * max_nr_gframes);
575 		if (shared == NULL) {
576 			printk(KERN_WARNING
577 					"Failed to ioremap gnttab share frames!");
578 			return -ENOMEM;
579 		}
580 	}
581 
582 	gnttab_map(0, nr_grant_frames - 1);
583 
584 	return 0;
585 }
586 
587 int gnttab_suspend(void)
588 {
589 	arch_gnttab_unmap_shared(shared, nr_grant_frames);
590 	return 0;
591 }
592 
593 static int gnttab_expand(unsigned int req_entries)
594 {
595 	int rc;
596 	unsigned int cur, extra;
597 
598 	cur = nr_grant_frames;
599 	extra = ((req_entries + (GREFS_PER_GRANT_FRAME-1)) /
600 		 GREFS_PER_GRANT_FRAME);
601 	if (cur + extra > gnttab_max_grant_frames())
602 		return -ENOSPC;
603 
604 	rc = gnttab_map(cur, cur + extra - 1);
605 	if (rc == 0)
606 		rc = grow_gnttab_list(extra);
607 
608 	return rc;
609 }
610 
611 int gnttab_init(void)
612 {
613 	int i;
614 	unsigned int max_nr_glist_frames, nr_glist_frames;
615 	unsigned int nr_init_grefs;
616 
617 	nr_grant_frames = 1;
618 	boot_max_nr_grant_frames = __max_nr_grant_frames();
619 
620 	/* Determine the maximum number of frames required for the
621 	 * grant reference free list on the current hypervisor.
622 	 */
623 	max_nr_glist_frames = (boot_max_nr_grant_frames *
624 			       GREFS_PER_GRANT_FRAME / RPP);
625 
626 	gnttab_list = kmalloc(max_nr_glist_frames * sizeof(grant_ref_t *),
627 			      GFP_KERNEL);
628 	if (gnttab_list == NULL)
629 		return -ENOMEM;
630 
631 	nr_glist_frames = (nr_grant_frames * GREFS_PER_GRANT_FRAME + RPP - 1) / RPP;
632 	for (i = 0; i < nr_glist_frames; i++) {
633 		gnttab_list[i] = (grant_ref_t *)__get_free_page(GFP_KERNEL);
634 		if (gnttab_list[i] == NULL)
635 			goto ini_nomem;
636 	}
637 
638 	if (gnttab_resume() < 0)
639 		return -ENODEV;
640 
641 	nr_init_grefs = nr_grant_frames * GREFS_PER_GRANT_FRAME;
642 
643 	for (i = NR_RESERVED_ENTRIES; i < nr_init_grefs - 1; i++)
644 		gnttab_entry(i) = i + 1;
645 
646 	gnttab_entry(nr_init_grefs - 1) = GNTTAB_LIST_END;
647 	gnttab_free_count = nr_init_grefs - NR_RESERVED_ENTRIES;
648 	gnttab_free_head  = NR_RESERVED_ENTRIES;
649 
650 	printk("Grant table initialized\n");
651 	return 0;
652 
653  ini_nomem:
654 	for (i--; i >= 0; i--)
655 		free_page((unsigned long)gnttab_list[i]);
656 	kfree(gnttab_list);
657 	return -ENOMEM;
658 }
659 EXPORT_SYMBOL_GPL(gnttab_init);
660 
661 static int __devinit __gnttab_init(void)
662 {
663 	/* Delay grant-table initialization in the PV on HVM case */
664 	if (xen_hvm_domain())
665 		return 0;
666 
667 	if (!xen_pv_domain())
668 		return -ENODEV;
669 
670 	return gnttab_init();
671 }
672 
673 core_initcall(__gnttab_init);
674