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#define pr_fmt(fmt) "xen:" KBUILD_MODNAME ": " fmt
52
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 /* It's possible for the target domain to map the just-allocated grant
173 * references by blindly guessing their IDs; if this is done, then
174 * __del_gref will leave them in the queue_gref list. They need to be
175 * added to the global list so that we can free them when they are no
176 * longer referenced.
177 */
178 if (unlikely(!list_empty(&queue_gref)))
179 list_splice_tail(&queue_gref, &gref_list);
180 mutex_unlock(&gref_mutex);
181 return rc;
182}
183
184static void __del_gref(struct gntalloc_gref *gref)
185{
186 if (gref->notify.flags & UNMAP_NOTIFY_CLEAR_BYTE) {
187 uint8_t *tmp = kmap(gref->page);
188 tmp[gref->notify.pgoff] = 0;
189 kunmap(gref->page);
190 }
191 if (gref->notify.flags & UNMAP_NOTIFY_SEND_EVENT) {
192 notify_remote_via_evtchn(gref->notify.event);
193 evtchn_put(gref->notify.event);
194 }
195
196 gref->notify.flags = 0;
197
198 if (gref->gref_id) {
199 if (gnttab_query_foreign_access(gref->gref_id))
200 return;
201
202 if (!gnttab_end_foreign_access_ref(gref->gref_id, 0))
203 return;
204
205 gnttab_free_grant_reference(gref->gref_id);
206 }
207
208 gref_size--;
209 list_del(&gref->next_gref);
210
211 if (gref->page)
212 __free_page(gref->page);
213
214 kfree(gref);
215}
216
217/* finds contiguous grant references in a file, returns the first */
218static struct gntalloc_gref *find_grefs(struct gntalloc_file_private_data *priv,
219 uint64_t index, uint32_t count)
220{
221 struct gntalloc_gref *rv = NULL, *gref;
222 list_for_each_entry(gref, &priv->list, next_file) {
223 if (gref->file_index == index && !rv)
224 rv = gref;
225 if (rv) {
226 if (gref->file_index != index)
227 return NULL;
228 index += PAGE_SIZE;
229 count--;
230 if (count == 0)
231 return rv;
232 }
233 }
234 return NULL;
235}
236
237/*
238 * -------------------------------------
239 * File operations.
240 * -------------------------------------
241 */
242static int gntalloc_open(struct inode *inode, struct file *filp)
243{
244 struct gntalloc_file_private_data *priv;
245
246 priv = kzalloc(sizeof(*priv), GFP_KERNEL);
247 if (!priv)
248 goto out_nomem;
249 INIT_LIST_HEAD(&priv->list);
250
251 filp->private_data = priv;
252
253 pr_debug("%s: priv %p\n", __func__, priv);
254
255 return 0;
256
257out_nomem:
258 return -ENOMEM;
259}
260
261static int gntalloc_release(struct inode *inode, struct file *filp)
262{
263 struct gntalloc_file_private_data *priv = filp->private_data;
264 struct gntalloc_gref *gref;
265
266 pr_debug("%s: priv %p\n", __func__, priv);
267
268 mutex_lock(&gref_mutex);
269 while (!list_empty(&priv->list)) {
270 gref = list_entry(priv->list.next,
271 struct gntalloc_gref, next_file);
272 list_del(&gref->next_file);
273 gref->users--;
274 if (gref->users == 0)
275 __del_gref(gref);
276 }
277 kfree(priv);
278 mutex_unlock(&gref_mutex);
279
280 return 0;
281}
282
283static long gntalloc_ioctl_alloc(struct gntalloc_file_private_data *priv,
284 struct ioctl_gntalloc_alloc_gref __user *arg)
285{
286 int rc = 0;
287 struct ioctl_gntalloc_alloc_gref op;
288 uint32_t *gref_ids;
289
290 pr_debug("%s: priv %p\n", __func__, priv);
291
292 if (copy_from_user(&op, arg, sizeof(op))) {
293 rc = -EFAULT;
294 goto out;
295 }
296
297 gref_ids = kcalloc(op.count, sizeof(gref_ids[0]), GFP_KERNEL);
298 if (!gref_ids) {
299 rc = -ENOMEM;
300 goto out;
301 }
302
303 mutex_lock(&gref_mutex);
304 /* Clean up pages that were at zero (local) users but were still mapped
305 * by remote domains. Since those pages count towards the limit that we
306 * are about to enforce, removing them here is a good idea.
307 */
308 do_cleanup();
309 if (gref_size + op.count > limit) {
310 mutex_unlock(&gref_mutex);
311 rc = -ENOSPC;
312 goto out_free;
313 }
314 gref_size += op.count;
315 op.index = priv->index;
316 priv->index += op.count * PAGE_SIZE;
317 mutex_unlock(&gref_mutex);
318
319 rc = add_grefs(&op, gref_ids, priv);
320 if (rc < 0)
321 goto out_free;
322
323 /* Once we finish add_grefs, it is unsafe to touch the new reference,
324 * since it is possible for a concurrent ioctl to remove it (by guessing
325 * its index). If the userspace application doesn't provide valid memory
326 * to write the IDs to, then it will need to close the file in order to
327 * release - which it will do by segfaulting when it tries to access the
328 * IDs to close them.
329 */
330 if (copy_to_user(arg, &op, sizeof(op))) {
331 rc = -EFAULT;
332 goto out_free;
333 }
334 if (copy_to_user(arg->gref_ids, gref_ids,
335 sizeof(gref_ids[0]) * op.count)) {
336 rc = -EFAULT;
337 goto out_free;
338 }
339
340out_free:
341 kfree(gref_ids);
342out:
343 return rc;
344}
345
346static long gntalloc_ioctl_dealloc(struct gntalloc_file_private_data *priv,
347 void __user *arg)
348{
349 int i, rc = 0;
350 struct ioctl_gntalloc_dealloc_gref op;
351 struct gntalloc_gref *gref, *n;
352
353 pr_debug("%s: priv %p\n", __func__, priv);
354
355 if (copy_from_user(&op, arg, sizeof(op))) {
356 rc = -EFAULT;
357 goto dealloc_grant_out;
358 }
359
360 mutex_lock(&gref_mutex);
361 gref = find_grefs(priv, op.index, op.count);
362 if (gref) {
363 /* Remove from the file list only, and decrease reference count.
364 * The later call to do_cleanup() will remove from gref_list and
365 * free the memory if the pages aren't mapped anywhere.
366 */
367 for (i = 0; i < op.count; i++) {
368 n = list_entry(gref->next_file.next,
369 struct gntalloc_gref, next_file);
370 list_del(&gref->next_file);
371 gref->users--;
372 gref = n;
373 }
374 } else {
375 rc = -EINVAL;
376 }
377
378 do_cleanup();
379
380 mutex_unlock(&gref_mutex);
381dealloc_grant_out:
382 return rc;
383}
384
385static long gntalloc_ioctl_unmap_notify(struct gntalloc_file_private_data *priv,
386 void __user *arg)
387{
388 struct ioctl_gntalloc_unmap_notify op;
389 struct gntalloc_gref *gref;
390 uint64_t index;
391 int pgoff;
392 int rc;
393
394 if (copy_from_user(&op, arg, sizeof(op)))
395 return -EFAULT;
396
397 index = op.index & ~(PAGE_SIZE - 1);
398 pgoff = op.index & (PAGE_SIZE - 1);
399
400 mutex_lock(&gref_mutex);
401
402 gref = find_grefs(priv, index, 1);
403 if (!gref) {
404 rc = -ENOENT;
405 goto unlock_out;
406 }
407
408 if (op.action & ~(UNMAP_NOTIFY_CLEAR_BYTE|UNMAP_NOTIFY_SEND_EVENT)) {
409 rc = -EINVAL;
410 goto unlock_out;
411 }
412
413 /* We need to grab a reference to the event channel we are going to use
414 * to send the notify before releasing the reference we may already have
415 * (if someone has called this ioctl twice). This is required so that
416 * it is possible to change the clear_byte part of the notification
417 * without disturbing the event channel part, which may now be the last
418 * reference to that event channel.
419 */
420 if (op.action & UNMAP_NOTIFY_SEND_EVENT) {
421 if (evtchn_get(op.event_channel_port)) {
422 rc = -EINVAL;
423 goto unlock_out;
424 }
425 }
426
427 if (gref->notify.flags & UNMAP_NOTIFY_SEND_EVENT)
428 evtchn_put(gref->notify.event);
429
430 gref->notify.flags = op.action;
431 gref->notify.pgoff = pgoff;
432 gref->notify.event = op.event_channel_port;
433 rc = 0;
434
435 unlock_out:
436 mutex_unlock(&gref_mutex);
437 return rc;
438}
439
440static long gntalloc_ioctl(struct file *filp, unsigned int cmd,
441 unsigned long arg)
442{
443 struct gntalloc_file_private_data *priv = filp->private_data;
444
445 switch (cmd) {
446 case IOCTL_GNTALLOC_ALLOC_GREF:
447 return gntalloc_ioctl_alloc(priv, (void __user *)arg);
448
449 case IOCTL_GNTALLOC_DEALLOC_GREF:
450 return gntalloc_ioctl_dealloc(priv, (void __user *)arg);
451
452 case IOCTL_GNTALLOC_SET_UNMAP_NOTIFY:
453 return gntalloc_ioctl_unmap_notify(priv, (void __user *)arg);
454
455 default:
456 return -ENOIOCTLCMD;
457 }
458
459 return 0;
460}
461
462static void gntalloc_vma_open(struct vm_area_struct *vma)
463{
464 struct gntalloc_vma_private_data *priv = vma->vm_private_data;
465
466 if (!priv)
467 return;
468
469 mutex_lock(&gref_mutex);
470 priv->users++;
471 mutex_unlock(&gref_mutex);
472}
473
474static void gntalloc_vma_close(struct vm_area_struct *vma)
475{
476 struct gntalloc_vma_private_data *priv = vma->vm_private_data;
477 struct gntalloc_gref *gref, *next;
478 int i;
479
480 if (!priv)
481 return;
482
483 mutex_lock(&gref_mutex);
484 priv->users--;
485 if (priv->users == 0) {
486 gref = priv->gref;
487 for (i = 0; i < priv->count; i++) {
488 gref->users--;
489 next = list_entry(gref->next_gref.next,
490 struct gntalloc_gref, next_gref);
491 if (gref->users == 0)
492 __del_gref(gref);
493 gref = next;
494 }
495 kfree(priv);
496 }
497 mutex_unlock(&gref_mutex);
498}
499
500static const struct vm_operations_struct gntalloc_vmops = {
501 .open = gntalloc_vma_open,
502 .close = gntalloc_vma_close,
503};
504
505static int gntalloc_mmap(struct file *filp, struct vm_area_struct *vma)
506{
507 struct gntalloc_file_private_data *priv = filp->private_data;
508 struct gntalloc_vma_private_data *vm_priv;
509 struct gntalloc_gref *gref;
510 int count = vma_pages(vma);
511 int rv, i;
512
513 if (!(vma->vm_flags & VM_SHARED)) {
514 pr_err("%s: Mapping must be shared\n", __func__);
515 return -EINVAL;
516 }
517
518 vm_priv = kmalloc(sizeof(*vm_priv), GFP_KERNEL);
519 if (!vm_priv)
520 return -ENOMEM;
521
522 mutex_lock(&gref_mutex);
523
524 pr_debug("%s: priv %p,%p, page %lu+%d\n", __func__,
525 priv, vm_priv, vma->vm_pgoff, count);
526
527 gref = find_grefs(priv, vma->vm_pgoff << PAGE_SHIFT, count);
528 if (gref == NULL) {
529 rv = -ENOENT;
530 pr_debug("%s: Could not find grant reference",
531 __func__);
532 kfree(vm_priv);
533 goto out_unlock;
534 }
535
536 vm_priv->gref = gref;
537 vm_priv->users = 1;
538 vm_priv->count = count;
539
540 vma->vm_private_data = vm_priv;
541
542 vma->vm_flags |= VM_DONTEXPAND | VM_DONTDUMP;
543
544 vma->vm_ops = &gntalloc_vmops;
545
546 for (i = 0; i < count; i++) {
547 gref->users++;
548 rv = vm_insert_page(vma, vma->vm_start + i * PAGE_SIZE,
549 gref->page);
550 if (rv)
551 goto out_unlock;
552
553 gref = list_entry(gref->next_file.next,
554 struct gntalloc_gref, next_file);
555 }
556 rv = 0;
557
558out_unlock:
559 mutex_unlock(&gref_mutex);
560 return rv;
561}
562
563static const struct file_operations gntalloc_fops = {
564 .owner = THIS_MODULE,
565 .open = gntalloc_open,
566 .release = gntalloc_release,
567 .unlocked_ioctl = gntalloc_ioctl,
568 .mmap = gntalloc_mmap
569};
570
571/*
572 * -------------------------------------
573 * Module creation/destruction.
574 * -------------------------------------
575 */
576static struct miscdevice gntalloc_miscdev = {
577 .minor = MISC_DYNAMIC_MINOR,
578 .name = "xen/gntalloc",
579 .fops = &gntalloc_fops,
580};
581
582static int __init gntalloc_init(void)
583{
584 int err;
585
586 if (!xen_domain())
587 return -ENODEV;
588
589 err = misc_register(&gntalloc_miscdev);
590 if (err != 0) {
591 pr_err("Could not register misc gntalloc device\n");
592 return err;
593 }
594
595 pr_debug("Created grant allocation device at %d,%d\n",
596 MISC_MAJOR, gntalloc_miscdev.minor);
597
598 return 0;
599}
600
601static void __exit gntalloc_exit(void)
602{
603 misc_deregister(&gntalloc_miscdev);
604}
605
606module_init(gntalloc_init);
607module_exit(gntalloc_exit);
608
609MODULE_LICENSE("GPL");
610MODULE_AUTHOR("Carter Weatherly <carter.weatherly@jhuapl.edu>, "
611 "Daniel De Graaf <dgdegra@tycho.nsa.gov>");
612MODULE_DESCRIPTION("User-space grant reference allocator driver");
613