aboutsummaryrefslogtreecommitdiffstats
path: root/drivers/xen/gntalloc.c
blob: a7ffdfe19fc9b06141792bde2d3ee10f61f10dbb (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
/******************************************************************************
 * gntalloc.c
 *
 * Device for creating grant references (in user-space) that may be shared
 * with other domains.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 */

/*
 * This driver exists to allow userspace programs in Linux to allocate kernel
 * memory that will later be shared with another domain.  Without this device,
 * Linux userspace programs cannot create grant references.
 *
 * How this stuff works:
 *   X -> granting a page to Y
 *   Y -> mapping the grant from X
 *
 *   1. X uses the gntalloc device to allocate a page of kernel memory, P.
 *   2. X creates an entry in the grant table that says domid(Y) can access P.
 *      This is done without a hypercall unless the grant table needs expansion.
 *   3. X gives the grant reference identifier, GREF, to Y.
 *   4. Y maps the page, either directly into kernel memory for use in a backend
 *      driver, or via a the gntdev device to map into the address space of an
 *      application running in Y. This is the first point at which Xen does any
 *      tracking of the page.
 *   5. A program in X mmap()s a segment of the gntalloc device that corresponds
 *      to the shared page, and can now communicate with Y over the shared page.
 *
 *
 * NOTE TO USERSPACE LIBRARIES:
 *   The grant allocation and mmap()ing are, naturally, two separate operations.
 *   You set up the sharing by calling the create ioctl() and then the mmap().
 *   Teardown requires munmap() and either close() or ioctl().
 *
 * WARNING: Since Xen does not allow a guest to forcibly end the use of a grant
 * reference, this device can be used to consume kernel memory by leaving grant
 * references mapped by another domain when an application exits. Therefore,
 * there is a global limit on the number of pages that can be allocated. When
 * all references to the page are unmapped, it will be freed during the next
 * grant operation.
 */

#include <linux/atomic.h>
#include <linux/module.h>
#include <linux/miscdevice.h>
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/slab.h>
#include <linux/fs.h>
#include <linux/device.h>
#include <linux/mm.h>
#include <linux/uaccess.h>
#include <linux/types.h>
#include <linux/list.h>
#include <linux/highmem.h>

#include <xen/xen.h>
#include <xen/page.h>
#include <xen/grant_table.h>
#include <xen/gntalloc.h>
#include <xen/events.h>

static int limit = 1024;
module_param(limit, int, 0644);
MODULE_PARM_DESC(limit, "Maximum number of grants that may be allocated by "
		"the gntalloc device");

static LIST_HEAD(gref_list);
static DEFINE_SPINLOCK(gref_lock);
static int gref_size;

struct notify_info {
	uint16_t pgoff:12;    /* Bits 0-11: Offset of the byte to clear */
	uint16_t flags:2;     /* Bits 12-13: Unmap notification flags */
	int event;            /* Port (event channel) to notify */
};

/* Metadata on a grant reference. */
struct gntalloc_gref {
	struct list_head next_gref;  /* list entry gref_list */
	struct list_head next_file;  /* list entry file->list, if open */
	struct page *page;	     /* The shared page */
	uint64_t file_index;         /* File offset for mmap() */
	unsigned int users;          /* Use count - when zero, waiting on Xen */
	grant_ref_t gref_id;         /* The grant reference number */
	struct notify_info notify;   /* Unmap notification */
};

struct gntalloc_file_private_data {
	struct list_head list;
	uint64_t index;
};

static void __del_gref(struct gntalloc_gref *gref);

static void do_cleanup(void)
{
	struct gntalloc_gref *gref, *n;
	list_for_each_entry_safe(gref, n, &gref_list, next_gref) {
		if (!gref->users)
			__del_gref(gref);
	}
}

static int add_grefs(struct ioctl_gntalloc_alloc_gref *op,
	uint32_t *gref_ids, struct gntalloc_file_private_data *priv)
{
	int i, rc, readonly;
	LIST_HEAD(queue_gref);
	LIST_HEAD(queue_file);
	struct gntalloc_gref *gref;

	readonly = !(op->flags & GNTALLOC_FLAG_WRITABLE);
	rc = -ENOMEM;
	for (i = 0; i < op->count; i++) {
		gref = kzalloc(sizeof(*gref), GFP_KERNEL);
		if (!gref)
			goto undo;
		list_add_tail(&gref->next_gref, &queue_gref);
		list_add_tail(&gref->next_file, &queue_file);
		gref->users = 1;
		gref->file_index = op->index + i * PAGE_SIZE;
		gref->page = alloc_page(GFP_KERNEL|__GFP_ZERO);
		if (!gref->page)
			goto undo;

		/* Grant foreign access to the page. */
		gref->gref_id = gnttab_grant_foreign_access(op->domid,
			pfn_to_mfn(page_to_pfn(gref->page)), readonly);
		if (gref->gref_id < 0) {
			rc = gref->gref_id;
			goto undo;
		}
		gref_ids[i] = gref->gref_id;
	}

	/* Add to gref lists. */
	spin_lock(&gref_lock);
	list_splice_tail(&queue_gref, &gref_list);
	list_splice_tail(&queue_file, &priv->list);
	spin_unlock(&gref_lock);

	return 0;

undo:
	spin_lock(&gref_lock);
	gref_size -= (op->count - i);

	list_for_each_entry(gref, &queue_file, next_file) {
		/* __del_gref does not remove from queue_file */
		__del_gref(gref);
	}

	/* It's possible for the target domain to map the just-allocated grant
	 * references by blindly guessing their IDs; if this is done, then
	 * __del_gref will leave them in the queue_gref list. They need to be
	 * added to the global list so that we can free them when they are no
	 * longer referenced.
	 */
	if (unlikely(!list_empty(&queue_gref)))
		list_splice_tail(&queue_gref, &gref_list);
	spin_unlock(&gref_lock);
	return rc;
}

static void __del_gref(struct gntalloc_gref *gref)
{
	if (gref->notify.flags & UNMAP_NOTIFY_CLEAR_BYTE) {
		uint8_t *tmp = kmap(gref->page);
		tmp[gref->notify.pgoff] = 0;
		kunmap(gref->page);
	}
	if (gref->notify.flags & UNMAP_NOTIFY_SEND_EVENT)
		notify_remote_via_evtchn(gref->notify.event);

	gref->notify.flags = 0;

	if (gref->gref_id > 0) {
		if (gnttab_query_foreign_access(gref->gref_id))
			return;

		if (!gnttab_end_foreign_access_ref(gref->gref_id, 0))
			return;
	}

	gref_size--;
	list_del(&gref->next_gref);

	if (gref->page)
		__free_page(gref->page);

	kfree(gref);
}

/* finds contiguous grant references in a file, returns the first */
static struct gntalloc_gref *find_grefs(struct gntalloc_file_private_data *priv,
		uint64_t index, uint32_t count)
{
	struct gntalloc_gref *rv = NULL, *gref;
	list_for_each_entry(gref, &priv->list, next_file) {
		if (gref->file_index == index && !rv)
			rv = gref;
		if (rv) {
			if (gref->file_index != index)
				return NULL;
			index += PAGE_SIZE;
			count--;
			if (count == 0)
				return rv;
		}
	}
	return NULL;
}

/*
 * -------------------------------------
 *  File operations.
 * -------------------------------------
 */
static int gntalloc_open(struct inode *inode, struct file *filp)
{
	struct gntalloc_file_private_data *priv;

	priv = kzalloc(sizeof(*priv), GFP_KERNEL);
	if (!priv)
		goto out_nomem;
	INIT_LIST_HEAD(&priv->list);

	filp->private_data = priv;

	pr_debug("%s: priv %p\n", __func__, priv);

	return 0;

out_nomem:
	return -ENOMEM;
}

static int gntalloc_release(struct inode *inode, struct file *filp)
{
	struct gntalloc_file_private_data *priv = filp->private_data;
	struct gntalloc_gref *gref;

	pr_debug("%s: priv %p\n", __func__, priv);

	spin_lock(&gref_lock);
	while (!list_empty(&priv->list)) {
		gref = list_entry(priv->list.next,
			struct gntalloc_gref, next_file);
		list_del(&gref->next_file);
		gref->users--;
		if (gref->users == 0)
			__del_gref(gref);
	}
	kfree(priv);
	spin_unlock(&gref_lock);

	return 0;
}

static long gntalloc_ioctl_alloc(struct gntalloc_file_private_data *priv,
		struct ioctl_gntalloc_alloc_gref __user *arg)
{
	int rc = 0;
	struct ioctl_gntalloc_alloc_gref op;
	uint32_t *gref_ids;

	pr_debug("%s: priv %p\n", __func__, priv);

	if (copy_from_user(&op, arg, sizeof(op))) {
		rc = -EFAULT;
		goto out;
	}

	gref_ids = kzalloc(sizeof(gref_ids[0]) * op.count, GFP_TEMPORARY);
	if (!gref_ids) {
		rc = -ENOMEM;
		goto out;
	}

	spin_lock(&gref_lock);
	/* Clean up pages that were at zero (local) users but were still mapped
	 * by remote domains. Since those pages count towards the limit that we
	 * are about to enforce, removing them here is a good idea.
	 */
	do_cleanup();
	if (gref_size + op.count > limit) {
		spin_unlock(&gref_lock);
		rc = -ENOSPC;
		goto out_free;
	}
	gref_size += op.count;
	op.index = priv->index;
	priv->index += op.count * PAGE_SIZE;
	spin_unlock(&gref_lock);

	rc = add_grefs(&op, gref_ids, priv);
	if (rc < 0)
		goto out_free;

	/* Once we finish add_grefs, it is unsafe to touch the new reference,
	 * since it is possible for a concurrent ioctl to remove it (by guessing
	 * its index). If the userspace application doesn't provide valid memory
	 * to write the IDs to, then it will need to close the file in order to
	 * release - which it will do by segfaulting when it tries to access the
	 * IDs to close them.
	 */
	if (copy_to_user(arg, &op, sizeof(op))) {
		rc = -EFAULT;
		goto out_free;
	}
	if (copy_to_user(arg->gref_ids, gref_ids,
			sizeof(gref_ids[0]) * op.count)) {
		rc = -EFAULT;
		goto out_free;
	}

out_free:
	kfree(gref_ids);
out:
	return rc;
}

static long gntalloc_ioctl_dealloc(struct gntalloc_file_private_data *priv,
		void __user *arg)
{
	int i, rc = 0;
	struct ioctl_gntalloc_dealloc_gref op;
	struct gntalloc_gref *gref, *n;

	pr_debug("%s: priv %p\n", __func__, priv);

	if (copy_from_user(&op, arg, sizeof(op))) {
		rc = -EFAULT;
		goto dealloc_grant_out;
	}

	spin_lock(&gref_lock);
	gref = find_grefs(priv, op.index, op.count);
	if (gref) {
		/* Remove from the file list only, and decrease reference count.
		 * The later call to do_cleanup() will remove from gref_list and
		 * free the memory if the pages aren't mapped anywhere.
		 */
		for (i = 0; i < op.count; i++) {
			n = list_entry(gref->next_file.next,
				struct gntalloc_gref, next_file);
			list_del(&gref->next_file);
			gref->users--;
			gref = n;
		}
	} else {
		rc = -EINVAL;
	}

	do_cleanup();

	spin_unlock(&gref_lock);
dealloc_grant_out:
	return rc;
}

static long gntalloc_ioctl_unmap_notify(struct gntalloc_file_private_data *priv,
		void __user *arg)
{
	struct ioctl_gntalloc_unmap_notify op;
	struct gntalloc_gref *gref;
	uint64_t index;
	int pgoff;
	int rc;

	if (copy_from_user(&op, arg, sizeof(op)))
		return -EFAULT;

	index = op.index & ~(PAGE_SIZE - 1);
	pgoff = op.index & (PAGE_SIZE - 1);

	spin_lock(&gref_lock);

	gref = find_grefs(priv, index, 1);
	if (!gref) {
		rc = -ENOENT;
		goto unlock_out;
	}

	if (op.action & ~(UNMAP_NOTIFY_CLEAR_BYTE|UNMAP_NOTIFY_SEND_EVENT)) {
		rc = -EINVAL;
		goto unlock_out;
	}

	gref->notify.flags = op.action;
	gref->notify.pgoff = pgoff;
	gref->notify.event = op.event_channel_port;
	rc = 0;
 unlock_out:
	spin_unlock(&gref_lock);
	return rc;
}

static long gntalloc_ioctl(struct file *filp, unsigned int cmd,
		unsigned long arg)
{
	struct gntalloc_file_private_data *priv = filp->private_data;

	switch (cmd) {
	case IOCTL_GNTALLOC_ALLOC_GREF:
		return gntalloc_ioctl_alloc(priv, (void __user *)arg);

	case IOCTL_GNTALLOC_DEALLOC_GREF:
		return gntalloc_ioctl_dealloc(priv, (void __user *)arg);

	case IOCTL_GNTALLOC_SET_UNMAP_NOTIFY:
		return gntalloc_ioctl_unmap_notify(priv, (void __user *)arg);

	default:
		return -ENOIOCTLCMD;
	}

	return 0;
}

static void gntalloc_vma_close(struct vm_area_struct *vma)
{
	struct gntalloc_gref *gref = vma->vm_private_data;
	if (!gref)
		return;

	spin_lock(&gref_lock);
	gref->users--;
	if (gref->users == 0)
		__del_gref(gref);
	spin_unlock(&gref_lock);
}

static struct vm_operations_struct gntalloc_vmops = {
	.close = gntalloc_vma_close,
};

static int gntalloc_mmap(struct file *filp, struct vm_area_struct *vma)
{
	struct gntalloc_file_private_data *priv = filp->private_data;
	struct gntalloc_gref *gref;
	int count = (vma->vm_end - vma->vm_start) >> PAGE_SHIFT;
	int rv, i;

	pr_debug("%s: priv %p, page %lu+%d\n", __func__,
		       priv, vma->vm_pgoff, count);

	if (!(vma->vm_flags & VM_SHARED)) {
		printk(KERN_ERR "%s: Mapping must be shared.\n", __func__);
		return -EINVAL;
	}

	spin_lock(&gref_lock);
	gref = find_grefs(priv, vma->vm_pgoff << PAGE_SHIFT, count);
	if (gref == NULL) {
		rv = -ENOENT;
		pr_debug("%s: Could not find grant reference",
				__func__);
		goto out_unlock;
	}

	vma->vm_private_data = gref;

	vma->vm_flags |= VM_RESERVED;
	vma->vm_flags |= VM_DONTCOPY;
	vma->vm_flags |= VM_PFNMAP | VM_PFN_AT_MMAP;

	vma->vm_ops = &gntalloc_vmops;

	for (i = 0; i < count; i++) {
		gref->users++;
		rv = vm_insert_page(vma, vma->vm_start + i * PAGE_SIZE,
				gref->page);
		if (rv)
			goto out_unlock;

		gref = list_entry(gref->next_file.next,
				struct gntalloc_gref, next_file);
	}
	rv = 0;

out_unlock:
	spin_unlock(&gref_lock);
	return rv;
}

static const struct file_operations gntalloc_fops = {
	.owner = THIS_MODULE,
	.open = gntalloc_open,
	.release = gntalloc_release,
	.unlocked_ioctl = gntalloc_ioctl,
	.mmap = gntalloc_mmap
};

/*
 * -------------------------------------
 * Module creation/destruction.
 * -------------------------------------
 */
static struct miscdevice gntalloc_miscdev = {
	.minor	= MISC_DYNAMIC_MINOR,
	.name	= "xen/gntalloc",
	.fops	= &gntalloc_fops,
};

static int __init gntalloc_init(void)
{
	int err;

	if (!xen_domain())
		return -ENODEV;

	err = misc_register(&gntalloc_miscdev);
	if (err != 0) {
		printk(KERN_ERR "Could not register misc gntalloc device\n");
		return err;
	}

	pr_debug("Created grant allocation device at %d,%d\n",
			MISC_MAJOR, gntalloc_miscdev.minor);

	return 0;
}

static void __exit gntalloc_exit(void)
{
	misc_deregister(&gntalloc_miscdev);
}

module_init(gntalloc_init);
module_exit(gntalloc_exit);

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Carter Weatherly <carter.weatherly@jhuapl.edu>, "
		"Daniel De Graaf <dgdegra@tycho.nsa.gov>");
MODULE_DESCRIPTION("User-space grant reference allocator driver");