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1/******************************************************************************2 * gntalloc.c3 *4 * Device for creating grant references (in user-space) that may be shared5 * 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 of9 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the10 * GNU General Public License for more details.11 *12 * You should have received a copy of the GNU General Public License13 * along with this program; if not, write to the Free Software14 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA15 */16 17/*18 * This driver exists to allow userspace programs in Linux to allocate kernel19 * 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 Y24 * Y -> mapping the grant from X25 *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 backend31 * driver, or via a the gntdev device to map into the address space of an32 * application running in Y. This is the first point at which Xen does any33 * tracking of the page.34 * 5. A program in X mmap()s a segment of the gntalloc device that corresponds35 * 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 grant44 * reference, this device can be used to consume kernel memory by leaving grant45 * 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. When47 * all references to the page are unmapped, it will be freed during the next48 * grant operation.49 */50 51#define pr_fmt(fmt) "xen:" KBUILD_MODNAME ": " fmt52 53#include <linux/atomic.h>54#include <linux/module.h>55#include <linux/miscdevice.h>56#include <linux/kernel.h>57#include <linux/init.h>58#include <linux/slab.h>59#include <linux/fs.h>60#include <linux/device.h>61#include <linux/mm.h>62#include <linux/uaccess.h>63#include <linux/types.h>64#include <linux/list.h>65#include <linux/highmem.h>66 67#include <xen/xen.h>68#include <xen/page.h>69#include <xen/grant_table.h>70#include <xen/gntalloc.h>71#include <xen/events.h>72 73static int limit = 1024;74module_param(limit, int, 0644);75MODULE_PARM_DESC(limit, "Maximum number of grants that may be allocated by "76 "the gntalloc device");77 78static LIST_HEAD(gref_list);79static DEFINE_MUTEX(gref_mutex);80static int gref_size;81 82struct notify_info {83 uint16_t pgoff:12; /* Bits 0-11: Offset of the byte to clear */84 uint16_t flags:2; /* Bits 12-13: Unmap notification flags */85 int event; /* Port (event channel) to notify */86};87 88/* Metadata on a grant reference. */89struct gntalloc_gref {90 struct list_head next_gref; /* list entry gref_list */91 struct list_head next_file; /* list entry file->list, if open */92 struct page *page; /* The shared page */93 uint64_t file_index; /* File offset for mmap() */94 unsigned int users; /* Use count - when zero, waiting on Xen */95 grant_ref_t gref_id; /* The grant reference number */96 struct notify_info notify; /* Unmap notification */97};98 99struct gntalloc_file_private_data {100 struct list_head list;101 uint64_t index;102};103 104struct gntalloc_vma_private_data {105 struct gntalloc_gref *gref;106 int users;107 int count;108};109 110static void __del_gref(struct gntalloc_gref *gref);111 112static void do_cleanup(void)113{114 struct gntalloc_gref *gref, *n;115 list_for_each_entry_safe(gref, n, &gref_list, next_gref) {116 if (!gref->users)117 __del_gref(gref);118 }119}120 121static int add_grefs(struct ioctl_gntalloc_alloc_gref *op,122 uint32_t *gref_ids, struct gntalloc_file_private_data *priv)123{124 int i, rc, readonly;125 LIST_HEAD(queue_gref);126 LIST_HEAD(queue_file);127 struct gntalloc_gref *gref, *next;128 129 readonly = !(op->flags & GNTALLOC_FLAG_WRITABLE);130 for (i = 0; i < op->count; i++) {131 gref = kzalloc(sizeof(*gref), GFP_KERNEL);132 if (!gref) {133 rc = -ENOMEM;134 goto undo;135 }136 list_add_tail(&gref->next_gref, &queue_gref);137 list_add_tail(&gref->next_file, &queue_file);138 gref->users = 1;139 gref->file_index = op->index + i * PAGE_SIZE;140 gref->page = alloc_page(GFP_KERNEL|__GFP_ZERO);141 if (!gref->page) {142 rc = -ENOMEM;143 goto undo;144 }145 146 /* Grant foreign access to the page. */147 rc = gnttab_grant_foreign_access(op->domid,148 xen_page_to_gfn(gref->page),149 readonly);150 if (rc < 0)151 goto undo;152 gref_ids[i] = gref->gref_id = rc;153 }154 155 /* Add to gref lists. */156 mutex_lock(&gref_mutex);157 list_splice_tail(&queue_gref, &gref_list);158 list_splice_tail(&queue_file, &priv->list);159 mutex_unlock(&gref_mutex);160 161 return 0;162 163undo:164 mutex_lock(&gref_mutex);165 gref_size -= (op->count - i);166 167 list_for_each_entry_safe(gref, next, &queue_file, next_file) {168 list_del(&gref->next_file);169 __del_gref(gref);170 }171 172 mutex_unlock(&gref_mutex);173 return rc;174}175 176static void __del_gref(struct gntalloc_gref *gref)177{178 if (gref->notify.flags & UNMAP_NOTIFY_CLEAR_BYTE) {179 uint8_t *tmp = kmap_local_page(gref->page);180 tmp[gref->notify.pgoff] = 0;181 kunmap_local(tmp);182 }183 if (gref->notify.flags & UNMAP_NOTIFY_SEND_EVENT) {184 notify_remote_via_evtchn(gref->notify.event);185 evtchn_put(gref->notify.event);186 }187 188 gref->notify.flags = 0;189 190 if (gref->gref_id) {191 if (gref->page)192 gnttab_end_foreign_access(gref->gref_id, gref->page);193 else194 gnttab_free_grant_reference(gref->gref_id);195 }196 197 gref_size--;198 list_del(&gref->next_gref);199 200 kfree(gref);201}202 203/* finds contiguous grant references in a file, returns the first */204static struct gntalloc_gref *find_grefs(struct gntalloc_file_private_data *priv,205 uint64_t index, uint32_t count)206{207 struct gntalloc_gref *rv = NULL, *gref;208 list_for_each_entry(gref, &priv->list, next_file) {209 if (gref->file_index == index && !rv)210 rv = gref;211 if (rv) {212 if (gref->file_index != index)213 return NULL;214 index += PAGE_SIZE;215 count--;216 if (count == 0)217 return rv;218 }219 }220 return NULL;221}222 223/*224 * -------------------------------------225 * File operations.226 * -------------------------------------227 */228static int gntalloc_open(struct inode *inode, struct file *filp)229{230 struct gntalloc_file_private_data *priv;231 232 priv = kzalloc(sizeof(*priv), GFP_KERNEL);233 if (!priv)234 goto out_nomem;235 INIT_LIST_HEAD(&priv->list);236 237 filp->private_data = priv;238 239 pr_debug("%s: priv %p\n", __func__, priv);240 241 return 0;242 243out_nomem:244 return -ENOMEM;245}246 247static int gntalloc_release(struct inode *inode, struct file *filp)248{249 struct gntalloc_file_private_data *priv = filp->private_data;250 struct gntalloc_gref *gref;251 252 pr_debug("%s: priv %p\n", __func__, priv);253 254 mutex_lock(&gref_mutex);255 while (!list_empty(&priv->list)) {256 gref = list_entry(priv->list.next,257 struct gntalloc_gref, next_file);258 list_del(&gref->next_file);259 gref->users--;260 if (gref->users == 0)261 __del_gref(gref);262 }263 kfree(priv);264 mutex_unlock(&gref_mutex);265 266 return 0;267}268 269static long gntalloc_ioctl_alloc(struct gntalloc_file_private_data *priv,270 struct ioctl_gntalloc_alloc_gref __user *arg)271{272 int rc = 0;273 struct ioctl_gntalloc_alloc_gref op;274 uint32_t *gref_ids;275 276 pr_debug("%s: priv %p\n", __func__, priv);277 278 if (copy_from_user(&op, arg, sizeof(op))) {279 rc = -EFAULT;280 goto out;281 }282 283 gref_ids = kcalloc(op.count, sizeof(gref_ids[0]), GFP_KERNEL);284 if (!gref_ids) {285 rc = -ENOMEM;286 goto out;287 }288 289 mutex_lock(&gref_mutex);290 /* Clean up pages that were at zero (local) users but were still mapped291 * by remote domains. Since those pages count towards the limit that we292 * are about to enforce, removing them here is a good idea.293 */294 do_cleanup();295 if (gref_size + op.count > limit) {296 mutex_unlock(&gref_mutex);297 rc = -ENOSPC;298 goto out_free;299 }300 gref_size += op.count;301 op.index = priv->index;302 priv->index += op.count * PAGE_SIZE;303 mutex_unlock(&gref_mutex);304 305 rc = add_grefs(&op, gref_ids, priv);306 if (rc < 0)307 goto out_free;308 309 /* Once we finish add_grefs, it is unsafe to touch the new reference,310 * since it is possible for a concurrent ioctl to remove it (by guessing311 * its index). If the userspace application doesn't provide valid memory312 * to write the IDs to, then it will need to close the file in order to313 * release - which it will do by segfaulting when it tries to access the314 * IDs to close them.315 */316 if (copy_to_user(arg, &op, sizeof(op))) {317 rc = -EFAULT;318 goto out_free;319 }320 if (copy_to_user(arg->gref_ids_flex, gref_ids,321 sizeof(gref_ids[0]) * op.count)) {322 rc = -EFAULT;323 goto out_free;324 }325 326out_free:327 kfree(gref_ids);328out:329 return rc;330}331 332static long gntalloc_ioctl_dealloc(struct gntalloc_file_private_data *priv,333 void __user *arg)334{335 int i, rc = 0;336 struct ioctl_gntalloc_dealloc_gref op;337 struct gntalloc_gref *gref, *n;338 339 pr_debug("%s: priv %p\n", __func__, priv);340 341 if (copy_from_user(&op, arg, sizeof(op))) {342 rc = -EFAULT;343 goto dealloc_grant_out;344 }345 346 mutex_lock(&gref_mutex);347 gref = find_grefs(priv, op.index, op.count);348 if (gref) {349 /* Remove from the file list only, and decrease reference count.350 * The later call to do_cleanup() will remove from gref_list and351 * free the memory if the pages aren't mapped anywhere.352 */353 for (i = 0; i < op.count; i++) {354 n = list_entry(gref->next_file.next,355 struct gntalloc_gref, next_file);356 list_del(&gref->next_file);357 gref->users--;358 gref = n;359 }360 } else {361 rc = -EINVAL;362 }363 364 do_cleanup();365 366 mutex_unlock(&gref_mutex);367dealloc_grant_out:368 return rc;369}370 371static long gntalloc_ioctl_unmap_notify(struct gntalloc_file_private_data *priv,372 void __user *arg)373{374 struct ioctl_gntalloc_unmap_notify op;375 struct gntalloc_gref *gref;376 uint64_t index;377 int pgoff;378 int rc;379 380 if (copy_from_user(&op, arg, sizeof(op)))381 return -EFAULT;382 383 index = op.index & ~(PAGE_SIZE - 1);384 pgoff = op.index & (PAGE_SIZE - 1);385 386 mutex_lock(&gref_mutex);387 388 gref = find_grefs(priv, index, 1);389 if (!gref) {390 rc = -ENOENT;391 goto unlock_out;392 }393 394 if (op.action & ~(UNMAP_NOTIFY_CLEAR_BYTE|UNMAP_NOTIFY_SEND_EVENT)) {395 rc = -EINVAL;396 goto unlock_out;397 }398 399 /* We need to grab a reference to the event channel we are going to use400 * to send the notify before releasing the reference we may already have401 * (if someone has called this ioctl twice). This is required so that402 * it is possible to change the clear_byte part of the notification403 * without disturbing the event channel part, which may now be the last404 * reference to that event channel.405 */406 if (op.action & UNMAP_NOTIFY_SEND_EVENT) {407 if (evtchn_get(op.event_channel_port)) {408 rc = -EINVAL;409 goto unlock_out;410 }411 }412 413 if (gref->notify.flags & UNMAP_NOTIFY_SEND_EVENT)414 evtchn_put(gref->notify.event);415 416 gref->notify.flags = op.action;417 gref->notify.pgoff = pgoff;418 gref->notify.event = op.event_channel_port;419 rc = 0;420 421 unlock_out:422 mutex_unlock(&gref_mutex);423 return rc;424}425 426static long gntalloc_ioctl(struct file *filp, unsigned int cmd,427 unsigned long arg)428{429 struct gntalloc_file_private_data *priv = filp->private_data;430 431 switch (cmd) {432 case IOCTL_GNTALLOC_ALLOC_GREF:433 return gntalloc_ioctl_alloc(priv, (void __user *)arg);434 435 case IOCTL_GNTALLOC_DEALLOC_GREF:436 return gntalloc_ioctl_dealloc(priv, (void __user *)arg);437 438 case IOCTL_GNTALLOC_SET_UNMAP_NOTIFY:439 return gntalloc_ioctl_unmap_notify(priv, (void __user *)arg);440 441 default:442 return -ENOIOCTLCMD;443 }444 445 return 0;446}447 448static void gntalloc_vma_open(struct vm_area_struct *vma)449{450 struct gntalloc_vma_private_data *priv = vma->vm_private_data;451 452 if (!priv)453 return;454 455 mutex_lock(&gref_mutex);456 priv->users++;457 mutex_unlock(&gref_mutex);458}459 460static void gntalloc_vma_close(struct vm_area_struct *vma)461{462 struct gntalloc_vma_private_data *priv = vma->vm_private_data;463 struct gntalloc_gref *gref, *next;464 int i;465 466 if (!priv)467 return;468 469 mutex_lock(&gref_mutex);470 priv->users--;471 if (priv->users == 0) {472 gref = priv->gref;473 for (i = 0; i < priv->count; i++) {474 gref->users--;475 next = list_entry(gref->next_gref.next,476 struct gntalloc_gref, next_gref);477 if (gref->users == 0)478 __del_gref(gref);479 gref = next;480 }481 kfree(priv);482 }483 mutex_unlock(&gref_mutex);484}485 486static const struct vm_operations_struct gntalloc_vmops = {487 .open = gntalloc_vma_open,488 .close = gntalloc_vma_close,489};490 491static int gntalloc_mmap(struct file *filp, struct vm_area_struct *vma)492{493 struct gntalloc_file_private_data *priv = filp->private_data;494 struct gntalloc_vma_private_data *vm_priv;495 struct gntalloc_gref *gref;496 int count = vma_pages(vma);497 int rv, i;498 499 if (!(vma->vm_flags & VM_SHARED)) {500 pr_err("%s: Mapping must be shared\n", __func__);501 return -EINVAL;502 }503 504 vm_priv = kmalloc(sizeof(*vm_priv), GFP_KERNEL);505 if (!vm_priv)506 return -ENOMEM;507 508 mutex_lock(&gref_mutex);509 510 pr_debug("%s: priv %p,%p, page %lu+%d\n", __func__,511 priv, vm_priv, vma->vm_pgoff, count);512 513 gref = find_grefs(priv, vma->vm_pgoff << PAGE_SHIFT, count);514 if (gref == NULL) {515 rv = -ENOENT;516 pr_debug("%s: Could not find grant reference",517 __func__);518 kfree(vm_priv);519 goto out_unlock;520 }521 522 vm_priv->gref = gref;523 vm_priv->users = 1;524 vm_priv->count = count;525 526 vma->vm_private_data = vm_priv;527 528 vm_flags_set(vma, VM_DONTEXPAND | VM_DONTDUMP);529 530 vma->vm_ops = &gntalloc_vmops;531 532 for (i = 0; i < count; i++) {533 gref->users++;534 rv = vm_insert_page(vma, vma->vm_start + i * PAGE_SIZE,535 gref->page);536 if (rv)537 goto out_unlock;538 539 gref = list_entry(gref->next_file.next,540 struct gntalloc_gref, next_file);541 }542 rv = 0;543 544out_unlock:545 mutex_unlock(&gref_mutex);546 return rv;547}548 549static const struct file_operations gntalloc_fops = {550 .owner = THIS_MODULE,551 .open = gntalloc_open,552 .release = gntalloc_release,553 .unlocked_ioctl = gntalloc_ioctl,554 .mmap = gntalloc_mmap555};556 557/*558 * -------------------------------------559 * Module creation/destruction.560 * -------------------------------------561 */562static struct miscdevice gntalloc_miscdev = {563 .minor = MISC_DYNAMIC_MINOR,564 .name = "xen/gntalloc",565 .fops = &gntalloc_fops,566};567 568static int __init gntalloc_init(void)569{570 int err;571 572 if (!xen_domain())573 return -ENODEV;574 575 err = misc_register(&gntalloc_miscdev);576 if (err != 0) {577 pr_err("Could not register misc gntalloc device\n");578 return err;579 }580 581 pr_debug("Created grant allocation device at %d,%d\n",582 MISC_MAJOR, gntalloc_miscdev.minor);583 584 return 0;585}586 587static void __exit gntalloc_exit(void)588{589 misc_deregister(&gntalloc_miscdev);590}591 592module_init(gntalloc_init);593module_exit(gntalloc_exit);594 595MODULE_LICENSE("GPL");596MODULE_AUTHOR("Carter Weatherly <carter.weatherly@jhuapl.edu>, "597 "Daniel De Graaf <dgdegra@tycho.nsa.gov>");598MODULE_DESCRIPTION("User-space grant reference allocator driver");599