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	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		else
194			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 mapped
291	 * by remote domains. Since those pages count towards the limit that we
292	 * 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 guessing
311	 * its index). If the userspace application doesn't provide valid memory
312	 * to write the IDs to, then it will need to close the file in order to
313	 * release - which it will do by segfaulting when it tries to access the
314	 * 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 and
351		 * 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 use
400	 * to send the notify before releasing the reference we may already have
401	 * (if someone has called this ioctl twice). This is required so that
402	 * it is possible to change the clear_byte part of the notification
403	 * without disturbing the event channel part, which may now be the last
404	 * 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_mmap
555};
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