summaryrefslogtreecommitdiff
path: root/drivers/xen/xen-front-pgdir-shbuf.c
blob: b52e0fa595a992a9d5c0a321b9fed2b725ee3de3 (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
546
547
548
549
550
551
// SPDX-License-Identifier: GPL-2.0 OR MIT

/*
 * Xen frontend/backend page directory based shared buffer
 * helper module.
 *
 * Copyright (C) 2018 EPAM Systems Inc.
 *
 * Author: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
 */

#include <linux/module.h>
#include <linux/errno.h>
#include <linux/mm.h>

#include <asm/xen/hypervisor.h>
#include <xen/balloon.h>
#include <xen/xen.h>
#include <xen/xenbus.h>
#include <xen/interface/io/ring.h>

#include <xen/xen-front-pgdir-shbuf.h>

/**
 * This structure represents the structure of a shared page
 * that contains grant references to the pages of the shared
 * buffer. This structure is common to many Xen para-virtualized
 * protocols at include/xen/interface/io/
 */
struct xen_page_directory {
	grant_ref_t gref_dir_next_page;
#define XEN_GREF_LIST_END	0
	grant_ref_t gref[]; /* Variable length */
};

/**
 * Shared buffer ops which are differently implemented
 * depending on the allocation mode, e.g. if the buffer
 * is allocated by the corresponding backend or frontend.
 * Some of the operations.
 */
struct xen_front_pgdir_shbuf_ops {
	/*
	 * Calculate number of grefs required to handle this buffer,
	 * e.g. if grefs are required for page directory only or the buffer
	 * pages as well.
	 */
	void (*calc_num_grefs)(struct xen_front_pgdir_shbuf *buf);

	/* Fill page directory according to para-virtual display protocol. */
	void (*fill_page_dir)(struct xen_front_pgdir_shbuf *buf);

	/* Claim grant references for the pages of the buffer. */
	int (*grant_refs_for_buffer)(struct xen_front_pgdir_shbuf *buf,
				     grant_ref_t *priv_gref_head, int gref_idx);

	/* Map grant references of the buffer. */
	int (*map)(struct xen_front_pgdir_shbuf *buf);

	/* Unmap grant references of the buffer. */
	int (*unmap)(struct xen_front_pgdir_shbuf *buf);
};

/**
 * Get granted reference to the very first page of the
 * page directory. Usually this is passed to the backend,
 * so it can find/fill the grant references to the buffer's
 * pages.
 *
 * \param buf shared buffer which page directory is of interest.
 * \return granted reference to the very first page of the
 * page directory.
 */
grant_ref_t
xen_front_pgdir_shbuf_get_dir_start(struct xen_front_pgdir_shbuf *buf)
{
	if (!buf->grefs)
		return INVALID_GRANT_REF;

	return buf->grefs[0];
}
EXPORT_SYMBOL_GPL(xen_front_pgdir_shbuf_get_dir_start);

/**
 * Map granted references of the shared buffer.
 *
 * Depending on the shared buffer mode of allocation
 * (be_alloc flag) this can either do nothing (for buffers
 * shared by the frontend itself) or map the provided granted
 * references onto the backing storage (buf->pages).
 *
 * \param buf shared buffer which grants to be mapped.
 * \return zero on success or a negative number on failure.
 */
int xen_front_pgdir_shbuf_map(struct xen_front_pgdir_shbuf *buf)
{
	if (buf->ops && buf->ops->map)
		return buf->ops->map(buf);

	/* No need to map own grant references. */
	return 0;
}
EXPORT_SYMBOL_GPL(xen_front_pgdir_shbuf_map);

/**
 * Unmap granted references of the shared buffer.
 *
 * Depending on the shared buffer mode of allocation
 * (be_alloc flag) this can either do nothing (for buffers
 * shared by the frontend itself) or unmap the provided granted
 * references.
 *
 * \param buf shared buffer which grants to be unmapped.
 * \return zero on success or a negative number on failure.
 */
int xen_front_pgdir_shbuf_unmap(struct xen_front_pgdir_shbuf *buf)
{
	if (buf->ops && buf->ops->unmap)
		return buf->ops->unmap(buf);

	/* No need to unmap own grant references. */
	return 0;
}
EXPORT_SYMBOL_GPL(xen_front_pgdir_shbuf_unmap);

/**
 * Free all the resources of the shared buffer.
 *
 * \param buf shared buffer which resources to be freed.
 */
void xen_front_pgdir_shbuf_free(struct xen_front_pgdir_shbuf *buf)
{
	if (buf->grefs) {
		int i;

		for (i = 0; i < buf->num_grefs; i++)
			if (buf->grefs[i] != INVALID_GRANT_REF)
				gnttab_end_foreign_access(buf->grefs[i], NULL);
	}
	kfree(buf->grefs);
	kfree(buf->directory);
}
EXPORT_SYMBOL_GPL(xen_front_pgdir_shbuf_free);

/*
 * Number of grefs a page can hold with respect to the
 * struct xen_page_directory header.
 */
#define XEN_NUM_GREFS_PER_PAGE ((PAGE_SIZE - \
				 offsetof(struct xen_page_directory, \
					  gref)) / sizeof(grant_ref_t))

/**
 * Get the number of pages the page directory consumes itself.
 *
 * \param buf shared buffer.
 */
static int get_num_pages_dir(struct xen_front_pgdir_shbuf *buf)
{
	return DIV_ROUND_UP(buf->num_pages, XEN_NUM_GREFS_PER_PAGE);
}

/**
 * Calculate the number of grant references needed to share the buffer
 * and its pages when backend allocates the buffer.
 *
 * \param buf shared buffer.
 */
static void backend_calc_num_grefs(struct xen_front_pgdir_shbuf *buf)
{
	/* Only for pages the page directory consumes itself. */
	buf->num_grefs = get_num_pages_dir(buf);
}

/**
 * Calculate the number of grant references needed to share the buffer
 * and its pages when frontend allocates the buffer.
 *
 * \param buf shared buffer.
 */
static void guest_calc_num_grefs(struct xen_front_pgdir_shbuf *buf)
{
	/*
	 * Number of pages the page directory consumes itself
	 * plus grefs for the buffer pages.
	 */
	buf->num_grefs = get_num_pages_dir(buf) + buf->num_pages;
}

#define xen_page_to_vaddr(page) \
	((uintptr_t)pfn_to_kaddr(page_to_xen_pfn(page)))

/**
 * Unmap the buffer previously mapped with grant references
 * provided by the backend.
 *
 * \param buf shared buffer.
 * \return zero on success or a negative number on failure.
 */
static int backend_unmap(struct xen_front_pgdir_shbuf *buf)
{
	struct gnttab_unmap_grant_ref *unmap_ops;
	int i, ret;

	if (!buf->pages || !buf->backend_map_handles || !buf->grefs)
		return 0;

	unmap_ops = kcalloc(buf->num_pages, sizeof(*unmap_ops),
			    GFP_KERNEL);
	if (!unmap_ops)
		return -ENOMEM;

	for (i = 0; i < buf->num_pages; i++) {
		phys_addr_t addr;

		addr = xen_page_to_vaddr(buf->pages[i]);
		gnttab_set_unmap_op(&unmap_ops[i], addr, GNTMAP_host_map,
				    buf->backend_map_handles[i]);
	}

	ret = gnttab_unmap_refs(unmap_ops, NULL, buf->pages,
				buf->num_pages);

	for (i = 0; i < buf->num_pages; i++) {
		if (unlikely(unmap_ops[i].status != GNTST_okay))
			dev_err(&buf->xb_dev->dev,
				"Failed to unmap page %d: %d\n",
				i, unmap_ops[i].status);
	}

	if (ret)
		dev_err(&buf->xb_dev->dev,
			"Failed to unmap grant references, ret %d", ret);

	kfree(unmap_ops);
	kfree(buf->backend_map_handles);
	buf->backend_map_handles = NULL;
	return ret;
}

/**
 * Map the buffer with grant references provided by the backend.
 *
 * \param buf shared buffer.
 * \return zero on success or a negative number on failure.
 */
static int backend_map(struct xen_front_pgdir_shbuf *buf)
{
	struct gnttab_map_grant_ref *map_ops = NULL;
	unsigned char *ptr;
	int ret, cur_gref, cur_dir_page, cur_page, grefs_left;

	map_ops = kcalloc(buf->num_pages, sizeof(*map_ops), GFP_KERNEL);
	if (!map_ops)
		return -ENOMEM;

	buf->backend_map_handles = kcalloc(buf->num_pages,
					   sizeof(*buf->backend_map_handles),
					   GFP_KERNEL);
	if (!buf->backend_map_handles) {
		kfree(map_ops);
		return -ENOMEM;
	}

	/*
	 * Read page directory to get grefs from the backend: for external
	 * buffer we only allocate buf->grefs for the page directory,
	 * so buf->num_grefs has number of pages in the page directory itself.
	 */
	ptr = buf->directory;
	grefs_left = buf->num_pages;
	cur_page = 0;
	for (cur_dir_page = 0; cur_dir_page < buf->num_grefs; cur_dir_page++) {
		struct xen_page_directory *page_dir =
			(struct xen_page_directory *)ptr;
		int to_copy = XEN_NUM_GREFS_PER_PAGE;

		if (to_copy > grefs_left)
			to_copy = grefs_left;

		for (cur_gref = 0; cur_gref < to_copy; cur_gref++) {
			phys_addr_t addr;

			addr = xen_page_to_vaddr(buf->pages[cur_page]);
			gnttab_set_map_op(&map_ops[cur_page], addr,
					  GNTMAP_host_map,
					  page_dir->gref[cur_gref],
					  buf->xb_dev->otherend_id);
			cur_page++;
		}

		grefs_left -= to_copy;
		ptr += PAGE_SIZE;
	}
	ret = gnttab_map_refs(map_ops, NULL, buf->pages, buf->num_pages);

	/* Save handles even if error, so we can unmap. */
	for (cur_page = 0; cur_page < buf->num_pages; cur_page++) {
		if (likely(map_ops[cur_page].status == GNTST_okay)) {
			buf->backend_map_handles[cur_page] =
				map_ops[cur_page].handle;
		} else {
			buf->backend_map_handles[cur_page] =
				INVALID_GRANT_HANDLE;
			if (!ret)
				ret = -ENXIO;
			dev_err(&buf->xb_dev->dev,
				"Failed to map page %d: %d\n",
				cur_page, map_ops[cur_page].status);
		}
	}

	if (ret) {
		dev_err(&buf->xb_dev->dev,
			"Failed to map grant references, ret %d", ret);
		backend_unmap(buf);
	}

	kfree(map_ops);
	return ret;
}

/**
 * Fill page directory with grant references to the pages of the
 * page directory itself.
 *
 * The grant references to the buffer pages are provided by the
 * backend in this case.
 *
 * \param buf shared buffer.
 */
static void backend_fill_page_dir(struct xen_front_pgdir_shbuf *buf)
{
	struct xen_page_directory *page_dir;
	unsigned char *ptr;
	int i, num_pages_dir;

	ptr = buf->directory;
	num_pages_dir = get_num_pages_dir(buf);

	/* Fill only grefs for the page directory itself. */
	for (i = 0; i < num_pages_dir - 1; i++) {
		page_dir = (struct xen_page_directory *)ptr;

		page_dir->gref_dir_next_page = buf->grefs[i + 1];
		ptr += PAGE_SIZE;
	}
	/* Last page must say there is no more pages. */
	page_dir = (struct xen_page_directory *)ptr;
	page_dir->gref_dir_next_page = XEN_GREF_LIST_END;
}

/**
 * Fill page directory with grant references to the pages of the
 * page directory and the buffer we share with the backend.
 *
 * \param buf shared buffer.
 */
static void guest_fill_page_dir(struct xen_front_pgdir_shbuf *buf)
{
	unsigned char *ptr;
	int cur_gref, grefs_left, to_copy, i, num_pages_dir;

	ptr = buf->directory;
	num_pages_dir = get_num_pages_dir(buf);

	/*
	 * While copying, skip grefs at start, they are for pages
	 * granted for the page directory itself.
	 */
	cur_gref = num_pages_dir;
	grefs_left = buf->num_pages;
	for (i = 0; i < num_pages_dir; i++) {
		struct xen_page_directory *page_dir =
			(struct xen_page_directory *)ptr;

		if (grefs_left <= XEN_NUM_GREFS_PER_PAGE) {
			to_copy = grefs_left;
			page_dir->gref_dir_next_page = XEN_GREF_LIST_END;
		} else {
			to_copy = XEN_NUM_GREFS_PER_PAGE;
			page_dir->gref_dir_next_page = buf->grefs[i + 1];
		}
		memcpy(&page_dir->gref, &buf->grefs[cur_gref],
		       to_copy * sizeof(grant_ref_t));
		ptr += PAGE_SIZE;
		grefs_left -= to_copy;
		cur_gref += to_copy;
	}
}

/**
 * Grant references to the frontend's buffer pages.
 *
 * These will be shared with the backend, so it can
 * access the buffer's data.
 *
 * \param buf shared buffer.
 * \return zero on success or a negative number on failure.
 */
static int guest_grant_refs_for_buffer(struct xen_front_pgdir_shbuf *buf,
				       grant_ref_t *priv_gref_head,
				       int gref_idx)
{
	int i, cur_ref, otherend_id;

	otherend_id = buf->xb_dev->otherend_id;
	for (i = 0; i < buf->num_pages; i++) {
		cur_ref = gnttab_claim_grant_reference(priv_gref_head);
		if (cur_ref < 0)
			return cur_ref;

		gnttab_grant_foreign_access_ref(cur_ref, otherend_id,
						xen_page_to_gfn(buf->pages[i]),
						0);
		buf->grefs[gref_idx++] = cur_ref;
	}
	return 0;
}

/**
 * Grant all the references needed to share the buffer.
 *
 * Grant references to the page directory pages and, if
 * needed, also to the pages of the shared buffer data.
 *
 * \param buf shared buffer.
 * \return zero on success or a negative number on failure.
 */
static int grant_references(struct xen_front_pgdir_shbuf *buf)
{
	grant_ref_t priv_gref_head;
	int ret, i, j, cur_ref;
	int otherend_id, num_pages_dir;

	ret = gnttab_alloc_grant_references(buf->num_grefs, &priv_gref_head);
	if (ret < 0) {
		dev_err(&buf->xb_dev->dev,
			"Cannot allocate grant references\n");
		return ret;
	}

	otherend_id = buf->xb_dev->otherend_id;
	j = 0;
	num_pages_dir = get_num_pages_dir(buf);
	for (i = 0; i < num_pages_dir; i++) {
		unsigned long frame;

		cur_ref = gnttab_claim_grant_reference(&priv_gref_head);
		if (cur_ref < 0)
			return cur_ref;

		frame = xen_page_to_gfn(virt_to_page(buf->directory +
						     PAGE_SIZE * i));
		gnttab_grant_foreign_access_ref(cur_ref, otherend_id, frame, 0);
		buf->grefs[j++] = cur_ref;
	}

	if (buf->ops->grant_refs_for_buffer) {
		ret = buf->ops->grant_refs_for_buffer(buf, &priv_gref_head, j);
		if (ret)
			return ret;
	}

	gnttab_free_grant_references(priv_gref_head);
	return 0;
}

/**
 * Allocate all required structures to mange shared buffer.
 *
 * \param buf shared buffer.
 * \return zero on success or a negative number on failure.
 */
static int alloc_storage(struct xen_front_pgdir_shbuf *buf)
{
	buf->grefs = kcalloc(buf->num_grefs, sizeof(*buf->grefs), GFP_KERNEL);
	if (!buf->grefs)
		return -ENOMEM;

	buf->directory = kcalloc(get_num_pages_dir(buf), PAGE_SIZE, GFP_KERNEL);
	if (!buf->directory)
		return -ENOMEM;

	return 0;
}

/*
 * For backend allocated buffers we don't need grant_refs_for_buffer
 * as those grant references are allocated at backend side.
 */
static const struct xen_front_pgdir_shbuf_ops backend_ops = {
	.calc_num_grefs = backend_calc_num_grefs,
	.fill_page_dir = backend_fill_page_dir,
	.map = backend_map,
	.unmap = backend_unmap
};

/*
 * For locally granted references we do not need to map/unmap
 * the references.
 */
static const struct xen_front_pgdir_shbuf_ops local_ops = {
	.calc_num_grefs = guest_calc_num_grefs,
	.fill_page_dir = guest_fill_page_dir,
	.grant_refs_for_buffer = guest_grant_refs_for_buffer,
};

/**
 * Allocate a new instance of a shared buffer.
 *
 * \param cfg configuration to be used while allocating a new shared buffer.
 * \return zero on success or a negative number on failure.
 */
int xen_front_pgdir_shbuf_alloc(struct xen_front_pgdir_shbuf_cfg *cfg)
{
	struct xen_front_pgdir_shbuf *buf = cfg->pgdir;
	int ret;

	if (cfg->be_alloc)
		buf->ops = &backend_ops;
	else
		buf->ops = &local_ops;
	buf->xb_dev = cfg->xb_dev;
	buf->num_pages = cfg->num_pages;
	buf->pages = cfg->pages;

	buf->ops->calc_num_grefs(buf);

	ret = alloc_storage(buf);
	if (ret)
		goto fail;

	ret = grant_references(buf);
	if (ret)
		goto fail;

	buf->ops->fill_page_dir(buf);

	return 0;

fail:
	xen_front_pgdir_shbuf_free(buf);
	return ret;
}
EXPORT_SYMBOL_GPL(xen_front_pgdir_shbuf_alloc);

MODULE_DESCRIPTION("Xen frontend/backend page directory based "
		   "shared buffer handling");
MODULE_AUTHOR("Oleksandr Andrushchenko");
MODULE_LICENSE("GPL");