Root/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
71static int limit = 1024;
72module_param(limit, int, 0644);
73MODULE_PARM_DESC(limit, "Maximum number of grants that may be allocated by "
74        "the gntalloc device");
75
76static LIST_HEAD(gref_list);
77static DEFINE_MUTEX(gref_mutex);
78static int gref_size;
79
80struct 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. */
87struct 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
97struct gntalloc_file_private_data {
98    struct list_head list;
99    uint64_t index;
100};
101
102struct gntalloc_vma_private_data {
103    struct gntalloc_gref *gref;
104    int users;
105    int count;
106};
107
108static void __del_gref(struct gntalloc_gref *gref);
109
110static 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
119static 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
159undo:
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
180static 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 */
214static 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 */
238static 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
253out_nomem:
254    return -ENOMEM;
255}
256
257static 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
279static 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
336out_free:
337    kfree(gref_ids);
338out:
339    return rc;
340}
341
342static 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);
377dealloc_grant_out:
378    return rc;
379}
380
381static 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
436static 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
458static 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
470static 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
496static struct vm_operations_struct gntalloc_vmops = {
497    .open = gntalloc_vma_open,
498    .close = gntalloc_vma_close,
499};
500
501static 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
554out_unlock:
555    mutex_unlock(&gref_mutex);
556    return rv;
557}
558
559static 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 */
572static struct miscdevice gntalloc_miscdev = {
573    .minor = MISC_DYNAMIC_MINOR,
574    .name = "xen/gntalloc",
575    .fops = &gntalloc_fops,
576};
577
578static 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
597static void __exit gntalloc_exit(void)
598{
599    misc_deregister(&gntalloc_miscdev);
600}
601
602module_init(gntalloc_init);
603module_exit(gntalloc_exit);
604
605MODULE_LICENSE("GPL");
606MODULE_AUTHOR("Carter Weatherly <carter.weatherly@jhuapl.edu>, "
607        "Daniel De Graaf <dgdegra@tycho.nsa.gov>");
608MODULE_DESCRIPTION("User-space grant reference allocator driver");
609

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