drivers/xen/gntalloc.c

   1 /******************************************************************************
   2  * gntalloc.c
   3  *
   4  * Device for creating grant references (in user-space) that may be shared
   5  * with other domains.
   6  *
   7  * This program is distributed in the hope that it will be useful,
   8  * but WITHOUT ANY WARRANTY; without even the implied warranty of
   9  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  10  * GNU General Public License for more details.
  11  *
  12  * You should have received a copy of the GNU General Public License
  13  * along with this program; if not, write to the Free Software
  14  * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
  15  */
  16
  17 /*
  18  * This driver exists to allow userspace programs in Linux to allocate kernel
  19  * memory that will later be shared with another domain.  Without this device,
  20  * Linux userspace programs cannot create grant references.
  21  *
  22  * How this stuff works:
  23  *   X -> granting a page to Y
  24  *   Y -> mapping the grant from X
  25  *
  26  *   1. X uses the gntalloc device to allocate a page of kernel memory, P.
  27  *   2. X creates an entry in the grant table that says domid(Y) can access P.
  28  *      This is done without a hypercall unless the grant table needs expansion.
  29  *   3. X gives the grant reference identifier, GREF, to Y.
  30  *   4. Y maps the page, either directly into kernel memory for use in a backend
  31  *      driver, or via a the gntdev device to map into the address space of an
  32  *      application running in Y. This is the first point at which Xen does any
  33  *      tracking of the page.
  34  *   5. A program in X mmap()s a segment of the gntalloc device that corresponds
  35  *      to the shared page, and can now communicate with Y over the shared page.
  36  *
  37  *
  38  * NOTE TO USERSPACE LIBRARIES:
  39  *   The grant allocation and mmap()ing are, naturally, two separate operations.
  40  *   You set up the sharing by calling the create ioctl() and then the mmap().
  41  *   Teardown requires munmap() and either close() or ioctl().
  42  *
  43  * WARNING: Since Xen does not allow a guest to forcibly end the use of a grant
  44  * reference, this device can be used to consume kernel memory by leaving grant
  45  * references mapped by another domain when an application exits. Therefore,
  46  * there is a global limit on the number of pages that can be allocated. When
  47  * all references to the page are unmapped, it will be freed during the next
  48  * grant operation.
  49  */
  50
  51 #include <linux/atomic.h>
  52 #include <linux/module.h>
  53 #include <linux/miscdevice.h>
  54 #include <linux/kernel.h>
  55 #include <linux/init.h>
  56 #include <linux/slab.h>
  57 #include <linux/fs.h>
  58 #include <linux/device.h>
  59 #include <linux/mm.h>
  60 #include <linux/uaccess.h>
  61 #include <linux/types.h>
  62 #include <linux/list.h>
  63 #include <linux/highmem.h>
  64
  65 #include <xen/xen.h>
  66 #include <xen/page.h>
  67 #include <xen/grant_table.h>
  68 #include <xen/gntalloc.h>
  69 #include <xen/events.h>
  70
  71 static int limit = 1024;
  72 module_param(limit, int, 0644);
  73 MODULE_PARM_DESC(limit, "Maximum number of grants that may be allocated by "
  74                 "the gntalloc device");
  75
  76 static LIST_HEAD(gref_list);
  77 static DEFINE_MUTEX(gref_mutex);
  78 static int gref_size;
  79
  80 struct notify_info {
  81         uint16_t pgoff:12;    /* Bits 0-11: Offset of the byte to clear */
  82         uint16_t flags:2;     /* Bits 12-13: Unmap notification flags */
  83         int event;            /* Port (event channel) to notify */
  84 };
  85
  86 /* Metadata on a grant reference. */
  87 struct gntalloc_gref {
  88         struct list_head next_gref;  /* list entry gref_list */
  89         struct list_head next_file;  /* list entry file->list, if open */
  90         struct page *page;           /* The shared page */
  91         uint64_t file_index;         /* File offset for mmap() */
  92         unsigned int users;          /* Use count - when zero, waiting on Xen */
  93         grant_ref_t gref_id;         /* The grant reference number */
  94         struct notify_info notify;   /* Unmap notification */
  95 };
  96
  97 struct gntalloc_file_private_data {
  98         struct list_head list;
  99         uint64_t index;
 100 };
 101
 102 struct gntalloc_vma_private_data {
 103         struct gntalloc_gref *gref;
 104         int users;
 105         int count;
 106 };
 107
 108 static void __del_gref(struct gntalloc_gref *gref);
 109
 110 static void do_cleanup(void)
 111 {
 112         struct gntalloc_gref *gref, *n;
 113         list_for_each_entry_safe(gref, n, &gref_list, next_gref) {
 114                 if (!gref->users)
 115                         __del_gref(gref);
 116         }
 117 }
 118
 119 static int add_grefs(struct ioctl_gntalloc_alloc_gref *op,
 120         uint32_t *gref_ids, struct gntalloc_file_private_data *priv)
 121 {
 122         int i, rc, readonly;
 123         LIST_HEAD(queue_gref);
 124         LIST_HEAD(queue_file);
 125         struct gntalloc_gref *gref;
 126
 127         readonly = !(op->flags & GNTALLOC_FLAG_WRITABLE);
 128         rc = -ENOMEM;
 129         for (i = 0; i < op->count; i++) {
 130                 gref = kzalloc(sizeof(*gref), GFP_KERNEL);
 131                 if (!gref)
 132                         goto undo;
 133                 list_add_tail(&gref->next_gref, &queue_gref);
 134                 list_add_tail(&gref->next_file, &queue_file);
 135                 gref->users = 1;
 136                 gref->file_index = op->index + i * PAGE_SIZE;
 137                 gref->page = alloc_page(GFP_KERNEL|__GFP_ZERO);
 138                 if (!gref->page)
 139                         goto undo;
 140
 141                 /* Grant foreign access to the page. */
 142                 gref->gref_id = gnttab_grant_foreign_access(op->domid,
 143                         pfn_to_mfn(page_to_pfn(gref->page)), readonly);
 144                 if ((int)gref->gref_id < 0) {
 145                         rc = gref->gref_id;
 146                         goto undo;
 147                 }
 148                 gref_ids[i] = gref->gref_id;
 149         }
 150
 151         /* Add to gref lists. */
 152         mutex_lock(&gref_mutex);
 153         list_splice_tail(&queue_gref, &gref_list);
 154         list_splice_tail(&queue_file, &priv->list);
 155         mutex_unlock(&gref_mutex);
 156
 157         return 0;
 158
 159 undo:
 160         mutex_lock(&gref_mutex);
 161         gref_size -= (op->count - i);
 162
 163         list_for_each_entry(gref, &queue_file, next_file) {
 164                 /* __del_gref does not remove from queue_file */
 165                 __del_gref(gref);
 166         }
 167
 168         /* It's possible for the target domain to map the just-allocated grant
 169          * references by blindly guessing their IDs; if this is done, then
 170          * __del_gref will leave them in the queue_gref list. They need to be
 171          * added to the global list so that we can free them when they are no
 172          * longer referenced.
 173          */
 174         if (unlikely(!list_empty(&queue_gref)))
 175                 list_splice_tail(&queue_gref, &gref_list);
 176         mutex_unlock(&gref_mutex);
 177         return rc;
 178 }
 179
 180 static void __del_gref(struct gntalloc_gref *gref)
 181 {
 182         if (gref->notify.flags & UNMAP_NOTIFY_CLEAR_BYTE) {
 183                 uint8_t *tmp = kmap(gref->page);
 184                 tmp[gref->notify.pgoff] = 0;
 185                 kunmap(gref->page);
 186         }
 187         if (gref->notify.flags & UNMAP_NOTIFY_SEND_EVENT) {
 188                 notify_remote_via_evtchn(gref->notify.event);
 189                 evtchn_put(gref->notify.event);
 190         }
 191
 192         gref->notify.flags = 0;
 193
 194         if (gref->gref_id > 0) {
 195                 if (gnttab_query_foreign_access(gref->gref_id))
 196                         return;
 197
 198                 if (!gnttab_end_foreign_access_ref(gref->gref_id, 0))
 199                         return;
 200
 201                 gnttab_free_grant_reference(gref->gref_id);
 202         }
 203
 204         gref_size--;
 205         list_del(&gref->next_gref);
 206
 207         if (gref->page)
 208                 __free_page(gref->page);
 209
 210         kfree(gref);
 211 }
 212
 213 /* finds contiguous grant references in a file, returns the first */
 214 static struct gntalloc_gref *find_grefs(struct gntalloc_file_private_data *priv,
 215                 uint64_t index, uint32_t count)
 216 {
 217         struct gntalloc_gref *rv = NULL, *gref;
 218         list_for_each_entry(gref, &priv->list, next_file) {
 219                 if (gref->file_index == index && !rv)
 220                         rv = gref;
 221                 if (rv) {
 222                         if (gref->file_index != index)
 223                                 return NULL;
 224                         index += PAGE_SIZE;
 225                         count--;
 226                         if (count == 0)
 227                                 return rv;
 228                 }
 229         }
 230         return NULL;
 231 }
 232
 233 /*
 234  * -------------------------------------
 235  *  File operations.
 236  * -------------------------------------
 237  */
 238 static int gntalloc_open(struct inode *inode, struct file *filp)
 239 {
 240         struct gntalloc_file_private_data *priv;
 241
 242         priv = kzalloc(sizeof(*priv), GFP_KERNEL);
 243         if (!priv)
 244                 goto out_nomem;
 245         INIT_LIST_HEAD(&priv->list);
 246
 247         filp->private_data = priv;
 248
 249         pr_debug("%s: priv %p\n", __func__, priv);
 250
 251         return 0;
 252
 253 out_nomem:
 254         return -ENOMEM;
 255 }
 256
 257 static int gntalloc_release(struct inode *inode, struct file *filp)
 258 {
 259         struct gntalloc_file_private_data *priv = filp->private_data;
 260         struct gntalloc_gref *gref;
 261
 262         pr_debug("%s: priv %p\n", __func__, priv);
 263
 264         mutex_lock(&gref_mutex);
 265         while (!list_empty(&priv->list)) {
 266                 gref = list_entry(priv->list.next,
 267                         struct gntalloc_gref, next_file);
 268                 list_del(&gref->next_file);
 269                 gref->users--;
 270                 if (gref->users == 0)
 271                         __del_gref(gref);
 272         }
 273         kfree(priv);
 274         mutex_unlock(&gref_mutex);
 275
 276         return 0;
 277 }
 278
 279 static long gntalloc_ioctl_alloc(struct gntalloc_file_private_data *priv,
 280                 struct ioctl_gntalloc_alloc_gref __user *arg)
 281 {
 282         int rc = 0;
 283         struct ioctl_gntalloc_alloc_gref op;
 284         uint32_t *gref_ids;
 285
 286         pr_debug("%s: priv %p\n", __func__, priv);
 287
 288         if (copy_from_user(&op, arg, sizeof(op))) {
 289                 rc = -EFAULT;
 290                 goto out;
 291         }
 292
 293         gref_ids = kcalloc(op.count, sizeof(gref_ids[0]), GFP_TEMPORARY);
 294         if (!gref_ids) {
 295                 rc = -ENOMEM;
 296                 goto out;
 297         }
 298
 299         mutex_lock(&gref_mutex);
 300         /* Clean up pages that were at zero (local) users but were still mapped
 301          * by remote domains. Since those pages count towards the limit that we
 302          * are about to enforce, removing them here is a good idea.
 303          */
 304         do_cleanup();
 305         if (gref_size + op.count > limit) {
 306                 mutex_unlock(&gref_mutex);
 307                 rc = -ENOSPC;
 308                 goto out_free;
 309         }
 310         gref_size += op.count;
 311         op.index = priv->index;
 312         priv->index += op.count * PAGE_SIZE;
 313         mutex_unlock(&gref_mutex);
 314
 315         rc = add_grefs(&op, gref_ids, priv);
 316         if (rc < 0)
 317                 goto out_free;
 318
 319         /* Once we finish add_grefs, it is unsafe to touch the new reference,
 320          * since it is possible for a concurrent ioctl to remove it (by guessing
 321          * its index). If the userspace application doesn't provide valid memory
 322          * to write the IDs to, then it will need to close the file in order to
 323          * release - which it will do by segfaulting when it tries to access the
 324          * IDs to close them.
 325          */
 326         if (copy_to_user(arg, &op, sizeof(op))) {
 327                 rc = -EFAULT;
 328                 goto out_free;
 329         }
 330         if (copy_to_user(arg->gref_ids, gref_ids,
 331                         sizeof(gref_ids[0]) * op.count)) {
 332                 rc = -EFAULT;
 333                 goto out_free;
 334         }
 335
 336 out_free:
 337         kfree(gref_ids);
 338 out:
 339         return rc;
 340 }
 341
 342 static long gntalloc_ioctl_dealloc(struct gntalloc_file_private_data *priv,
 343                 void __user *arg)
 344 {
 345         int i, rc = 0;
 346         struct ioctl_gntalloc_dealloc_gref op;
 347         struct gntalloc_gref *gref, *n;
 348
 349         pr_debug("%s: priv %p\n", __func__, priv);
 350
 351         if (copy_from_user(&op, arg, sizeof(op))) {
 352                 rc = -EFAULT;
 353                 goto dealloc_grant_out;
 354         }
 355
 356         mutex_lock(&gref_mutex);
 357         gref = find_grefs(priv, op.index, op.count);
 358         if (gref) {
 359                 /* Remove from the file list only, and decrease reference count.
 360                  * The later call to do_cleanup() will remove from gref_list and
 361                  * free the memory if the pages aren't mapped anywhere.
 362                  */
 363                 for (i = 0; i < op.count; i++) {
 364                         n = list_entry(gref->next_file.next,
 365                                 struct gntalloc_gref, next_file);
 366                         list_del(&gref->next_file);
 367                         gref->users--;
 368                         gref = n;
 369                 }
 370         } else {
 371                 rc = -EINVAL;
 372         }
 373
 374         do_cleanup();
 375
 376         mutex_unlock(&gref_mutex);
 377 dealloc_grant_out:
 378         return rc;
 379 }
 380
 381 static long gntalloc_ioctl_unmap_notify(struct gntalloc_file_private_data *priv,
 382                 void __user *arg)
 383 {
 384         struct ioctl_gntalloc_unmap_notify op;
 385         struct gntalloc_gref *gref;
 386         uint64_t index;
 387         int pgoff;
 388         int rc;
 389
 390         if (copy_from_user(&op, arg, sizeof(op)))
 391                 return -EFAULT;
 392
 393         index = op.index & ~(PAGE_SIZE - 1);
 394         pgoff = op.index & (PAGE_SIZE - 1);
 395
 396         mutex_lock(&gref_mutex);
 397
 398         gref = find_grefs(priv, index, 1);
 399         if (!gref) {
 400                 rc = -ENOENT;
 401                 goto unlock_out;
 402         }
 403
 404         if (op.action & ~(UNMAP_NOTIFY_CLEAR_BYTE|UNMAP_NOTIFY_SEND_EVENT)) {
 405                 rc = -EINVAL;
 406                 goto unlock_out;
 407         }
 408
 409         /* We need to grab a reference to the event channel we are going to use
 410          * to send the notify before releasing the reference we may already have
 411          * (if someone has called this ioctl twice). This is required so that
 412          * it is possible to change the clear_byte part of the notification
 413          * without disturbing the event channel part, which may now be the last
 414          * reference to that event channel.
 415          */
 416         if (op.action & UNMAP_NOTIFY_SEND_EVENT) {
 417                 if (evtchn_get(op.event_channel_port)) {
 418                         rc = -EINVAL;
 419                         goto unlock_out;
 420                 }
 421         }
 422
 423         if (gref->notify.flags & UNMAP_NOTIFY_SEND_EVENT)
 424                 evtchn_put(gref->notify.event);
 425
 426         gref->notify.flags = op.action;
 427         gref->notify.pgoff = pgoff;
 428         gref->notify.event = op.event_channel_port;
 429         rc = 0;
 430
 431  unlock_out:
 432         mutex_unlock(&gref_mutex);
 433         return rc;
 434 }
 435
 436 static long gntalloc_ioctl(struct file *filp, unsigned int cmd,
 437                 unsigned long arg)
 438 {
 439         struct gntalloc_file_private_data *priv = filp->private_data;
 440
 441         switch (cmd) {
 442         case IOCTL_GNTALLOC_ALLOC_GREF:
 443                 return gntalloc_ioctl_alloc(priv, (void __user *)arg);
 444
 445         case IOCTL_GNTALLOC_DEALLOC_GREF:
 446                 return gntalloc_ioctl_dealloc(priv, (void __user *)arg);
 447
 448         case IOCTL_GNTALLOC_SET_UNMAP_NOTIFY:
 449                 return gntalloc_ioctl_unmap_notify(priv, (void __user *)arg);
 450
 451         default:
 452                 return -ENOIOCTLCMD;
 453         }
 454
 455         return 0;
 456 }
 457
 458 static void gntalloc_vma_open(struct vm_area_struct *vma)
 459 {
 460         struct gntalloc_vma_private_data *priv = vma->vm_private_data;
 461
 462         if (!priv)
 463                 return;
 464
 465         mutex_lock(&gref_mutex);
 466         priv->users++;
 467         mutex_unlock(&gref_mutex);
 468 }
 469
 470 static void gntalloc_vma_close(struct vm_area_struct *vma)
 471 {
 472         struct gntalloc_vma_private_data *priv = vma->vm_private_data;
 473         struct gntalloc_gref *gref, *next;
 474         int i;
 475
 476         if (!priv)
 477                 return;
 478
 479         mutex_lock(&gref_mutex);
 480         priv->users--;
 481         if (priv->users == 0) {
 482                 gref = priv->gref;
 483                 for (i = 0; i < priv->count; i++) {
 484                         gref->users--;
 485                         next = list_entry(gref->next_gref.next,
 486                                           struct gntalloc_gref, next_gref);
 487                         if (gref->users == 0)
 488                                 __del_gref(gref);
 489                         gref = next;
 490                 }
 491                 kfree(priv);
 492         }
 493         mutex_unlock(&gref_mutex);
 494 }
 495
 496 static struct vm_operations_struct gntalloc_vmops = {
 497         .open = gntalloc_vma_open,
 498         .close = gntalloc_vma_close,
 499 };
 500
 501 static int gntalloc_mmap(struct file *filp, struct vm_area_struct *vma)
 502 {
 503         struct gntalloc_file_private_data *priv = filp->private_data;
 504         struct gntalloc_vma_private_data *vm_priv;
 505         struct gntalloc_gref *gref;
 506         int count = (vma->vm_end - vma->vm_start) >> PAGE_SHIFT;
 507         int rv, i;
 508
 509         if (!(vma->vm_flags & VM_SHARED)) {
 510                 printk(KERN_ERR "%s: Mapping must be shared.\n", __func__);
 511                 return -EINVAL;
 512         }
 513
 514         vm_priv = kmalloc(sizeof(*vm_priv), GFP_KERNEL);
 515         if (!vm_priv)
 516                 return -ENOMEM;
 517
 518         mutex_lock(&gref_mutex);
 519
 520         pr_debug("%s: priv %p,%p, page %lu+%d\n", __func__,
 521                        priv, vm_priv, vma->vm_pgoff, count);
 522
 523         gref = find_grefs(priv, vma->vm_pgoff << PAGE_SHIFT, count);
 524         if (gref == NULL) {
 525                 rv = -ENOENT;
 526                 pr_debug("%s: Could not find grant reference",
 527                                 __func__);
 528                 kfree(vm_priv);
 529                 goto out_unlock;
 530         }
 531
 532         vm_priv->gref = gref;
 533         vm_priv->users = 1;
 534         vm_priv->count = count;
 535
 536         vma->vm_private_data = vm_priv;
 537
 538         vma->vm_flags |= VM_RESERVED | VM_DONTEXPAND;
 539
 540         vma->vm_ops = &gntalloc_vmops;
 541
 542         for (i = 0; i < count; i++) {
 543                 gref->users++;
 544                 rv = vm_insert_page(vma, vma->vm_start + i * PAGE_SIZE,
 545                                 gref->page);
 546                 if (rv)
 547                         goto out_unlock;
 548
 549                 gref = list_entry(gref->next_file.next,
 550                                 struct gntalloc_gref, next_file);
 551         }
 552         rv = 0;
 553
 554 out_unlock:
 555         mutex_unlock(&gref_mutex);
 556         return rv;
 557 }
 558
 559 static const struct file_operations gntalloc_fops = {
 560         .owner = THIS_MODULE,
 561         .open = gntalloc_open,
 562         .release = gntalloc_release,
 563         .unlocked_ioctl = gntalloc_ioctl,
 564         .mmap = gntalloc_mmap
 565 };
 566
 567 /*
 568  * -------------------------------------
 569  * Module creation/destruction.
 570  * -------------------------------------
 571  */
 572 static struct miscdevice gntalloc_miscdev = {
 573         .minor  = MISC_DYNAMIC_MINOR,
 574         .name   = "xen/gntalloc",
 575         .fops   = &gntalloc_fops,
 576 };
 577
 578 static int __init gntalloc_init(void)
 579 {
 580         int err;
 581
 582         if (!xen_domain())
 583                 return -ENODEV;
 584
 585         err = misc_register(&gntalloc_miscdev);
 586         if (err != 0) {
 587                 printk(KERN_ERR "Could not register misc gntalloc device\n");
 588                 return err;
 589         }
 590
 591         pr_debug("Created grant allocation device at %d,%d\n",
 592                         MISC_MAJOR, gntalloc_miscdev.minor);
 593
 594         return 0;
 595 }
 596
 597 static void __exit gntalloc_exit(void)
 598 {
 599         misc_deregister(&gntalloc_miscdev);
 600 }
 601
 602 module_init(gntalloc_init);
 603 module_exit(gntalloc_exit);
 604
 605 MODULE_LICENSE("GPL");
 606 MODULE_AUTHOR("Carter Weatherly <carter.weatherly@jhuapl.edu>, "
 607                 "Daniel De Graaf <dgdegra@tycho.nsa.gov>");
 608 MODULE_DESCRIPTION("User-space grant reference allocator driver");