drivers/xen/grant-table.c

   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);