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1// SPDX-License-Identifier: GPL-2.0 OR MIT
2
3/*
4 * Xen frontend/backend page directory based shared buffer
5 * helper module.
6 *
7 * Copyright (C) 2018 EPAM Systems Inc.
8 *
9 * Author: Oleksandr Andrushchenko <[email protected]>
10 */
11
12#include <linux/module.h>
13#include <linux/errno.h>
14#include <linux/mm.h>
15
16#include <asm/xen/hypervisor.h>
17#include <xen/balloon.h>
18#include <xen/xen.h>
19#include <xen/xenbus.h>
20#include <xen/interface/io/ring.h>
21
22#include <xen/xen-front-pgdir-shbuf.h>
23
24/*
25 * This structure represents the structure of a shared page
26 * that contains grant references to the pages of the shared
27 * buffer. This structure is common to many Xen para-virtualized
28 * protocols at include/xen/interface/io/
29 */
30struct xen_page_directory {
31 grant_ref_t gref_dir_next_page;
32#define XEN_GREF_LIST_END 0
33 grant_ref_t gref[]; /* Variable length */
34};
35
36/*
37 * Shared buffer ops which are differently implemented
38 * depending on the allocation mode, e.g. if the buffer
39 * is allocated by the corresponding backend or frontend.
40 * Some of the operations.
41 */
42struct xen_front_pgdir_shbuf_ops {
43 /*
44 * Calculate number of grefs required to handle this buffer,
45 * e.g. if grefs are required for page directory only or the buffer
46 * pages as well.
47 */
48 void (*calc_num_grefs)(struct xen_front_pgdir_shbuf *buf);
49
50 /* Fill page directory according to para-virtual display protocol. */
51 void (*fill_page_dir)(struct xen_front_pgdir_shbuf *buf);
52
53 /* Claim grant references for the pages of the buffer. */
54 int (*grant_refs_for_buffer)(struct xen_front_pgdir_shbuf *buf,
55 grant_ref_t *priv_gref_head, int gref_idx);
56
57 /* Map grant references of the buffer. */
58 int (*map)(struct xen_front_pgdir_shbuf *buf);
59
60 /* Unmap grant references of the buffer. */
61 int (*unmap)(struct xen_front_pgdir_shbuf *buf);
62};
63
64/*
65 * Get granted reference to the very first page of the
66 * page directory. Usually this is passed to the backend,
67 * so it can find/fill the grant references to the buffer's
68 * pages.
69 *
70 * \param buf shared buffer which page directory is of interest.
71 * \return granted reference to the very first page of the
72 * page directory.
73 */
74grant_ref_t
75xen_front_pgdir_shbuf_get_dir_start(struct xen_front_pgdir_shbuf *buf)
76{
77 if (!buf->grefs)
78 return INVALID_GRANT_REF;
79
80 return buf->grefs[0];
81}
82EXPORT_SYMBOL_GPL(xen_front_pgdir_shbuf_get_dir_start);
83
84/*
85 * Map granted references of the shared buffer.
86 *
87 * Depending on the shared buffer mode of allocation
88 * (be_alloc flag) this can either do nothing (for buffers
89 * shared by the frontend itself) or map the provided granted
90 * references onto the backing storage (buf->pages).
91 *
92 * \param buf shared buffer which grants to be mapped.
93 * \return zero on success or a negative number on failure.
94 */
95int xen_front_pgdir_shbuf_map(struct xen_front_pgdir_shbuf *buf)
96{
97 if (buf->ops && buf->ops->map)
98 return buf->ops->map(buf);
99
100 /* No need to map own grant references. */
101 return 0;
102}
103EXPORT_SYMBOL_GPL(xen_front_pgdir_shbuf_map);
104
105/*
106 * Unmap granted references of the shared buffer.
107 *
108 * Depending on the shared buffer mode of allocation
109 * (be_alloc flag) this can either do nothing (for buffers
110 * shared by the frontend itself) or unmap the provided granted
111 * references.
112 *
113 * \param buf shared buffer which grants to be unmapped.
114 * \return zero on success or a negative number on failure.
115 */
116int xen_front_pgdir_shbuf_unmap(struct xen_front_pgdir_shbuf *buf)
117{
118 if (buf->ops && buf->ops->unmap)
119 return buf->ops->unmap(buf);
120
121 /* No need to unmap own grant references. */
122 return 0;
123}
124EXPORT_SYMBOL_GPL(xen_front_pgdir_shbuf_unmap);
125
126/*
127 * Free all the resources of the shared buffer.
128 *
129 * \param buf shared buffer which resources to be freed.
130 */
131void xen_front_pgdir_shbuf_free(struct xen_front_pgdir_shbuf *buf)
132{
133 if (buf->grefs) {
134 int i;
135
136 for (i = 0; i < buf->num_grefs; i++)
137 if (buf->grefs[i] != INVALID_GRANT_REF)
138 gnttab_end_foreign_access(buf->grefs[i], NULL);
139 }
140 kfree(buf->grefs);
141 kfree(buf->directory);
142}
143EXPORT_SYMBOL_GPL(xen_front_pgdir_shbuf_free);
144
145/*
146 * Number of grefs a page can hold with respect to the
147 * struct xen_page_directory header.
148 */
149#define XEN_NUM_GREFS_PER_PAGE ((PAGE_SIZE - \
150 offsetof(struct xen_page_directory, \
151 gref)) / sizeof(grant_ref_t))
152
153/*
154 * Get the number of pages the page directory consumes itself.
155 *
156 * \param buf shared buffer.
157 */
158static int get_num_pages_dir(struct xen_front_pgdir_shbuf *buf)
159{
160 return DIV_ROUND_UP(buf->num_pages, XEN_NUM_GREFS_PER_PAGE);
161}
162
163/*
164 * Calculate the number of grant references needed to share the buffer
165 * and its pages when backend allocates the buffer.
166 *
167 * \param buf shared buffer.
168 */
169static void backend_calc_num_grefs(struct xen_front_pgdir_shbuf *buf)
170{
171 /* Only for pages the page directory consumes itself. */
172 buf->num_grefs = get_num_pages_dir(buf);
173}
174
175/*
176 * Calculate the number of grant references needed to share the buffer
177 * and its pages when frontend allocates the buffer.
178 *
179 * \param buf shared buffer.
180 */
181static void guest_calc_num_grefs(struct xen_front_pgdir_shbuf *buf)
182{
183 /*
184 * Number of pages the page directory consumes itself
185 * plus grefs for the buffer pages.
186 */
187 buf->num_grefs = get_num_pages_dir(buf) + buf->num_pages;
188}
189
190#define xen_page_to_vaddr(page) \
191 ((uintptr_t)pfn_to_kaddr(page_to_xen_pfn(page)))
192
193/*
194 * Unmap the buffer previously mapped with grant references
195 * provided by the backend.
196 *
197 * \param buf shared buffer.
198 * \return zero on success or a negative number on failure.
199 */
200static int backend_unmap(struct xen_front_pgdir_shbuf *buf)
201{
202 struct gnttab_unmap_grant_ref *unmap_ops;
203 int i, ret;
204
205 if (!buf->pages || !buf->backend_map_handles || !buf->grefs)
206 return 0;
207
208 unmap_ops = kzalloc_objs(*unmap_ops, buf->num_pages);
209 if (!unmap_ops)
210 return -ENOMEM;
211
212 for (i = 0; i < buf->num_pages; i++) {
213 phys_addr_t addr;
214
215 addr = xen_page_to_vaddr(buf->pages[i]);
216 gnttab_set_unmap_op(&unmap_ops[i], addr, GNTMAP_host_map,
217 buf->backend_map_handles[i]);
218 }
219
220 ret = gnttab_unmap_refs(unmap_ops, NULL, buf->pages,
221 buf->num_pages);
222
223 for (i = 0; i < buf->num_pages; i++) {
224 if (unlikely(unmap_ops[i].status != GNTST_okay))
225 dev_err(&buf->xb_dev->dev,
226 "Failed to unmap page %d: %d\n",
227 i, unmap_ops[i].status);
228 }
229
230 if (ret)
231 dev_err(&buf->xb_dev->dev,
232 "Failed to unmap grant references, ret %d", ret);
233
234 kfree(unmap_ops);
235 kfree(buf->backend_map_handles);
236 buf->backend_map_handles = NULL;
237 return ret;
238}
239
240/*
241 * Map the buffer with grant references provided by the backend.
242 *
243 * \param buf shared buffer.
244 * \return zero on success or a negative number on failure.
245 */
246static int backend_map(struct xen_front_pgdir_shbuf *buf)
247{
248 struct gnttab_map_grant_ref *map_ops = NULL;
249 unsigned char *ptr;
250 int ret, cur_gref, cur_dir_page, cur_page, grefs_left;
251
252 map_ops = kzalloc_objs(*map_ops, buf->num_pages);
253 if (!map_ops)
254 return -ENOMEM;
255
256 buf->backend_map_handles = kzalloc_objs(*buf->backend_map_handles,
257 buf->num_pages);
258 if (!buf->backend_map_handles) {
259 kfree(map_ops);
260 return -ENOMEM;
261 }
262
263 /*
264 * Read page directory to get grefs from the backend: for external
265 * buffer we only allocate buf->grefs for the page directory,
266 * so buf->num_grefs has number of pages in the page directory itself.
267 */
268 ptr = buf->directory;
269 grefs_left = buf->num_pages;
270 cur_page = 0;
271 for (cur_dir_page = 0; cur_dir_page < buf->num_grefs; cur_dir_page++) {
272 struct xen_page_directory *page_dir =
273 (struct xen_page_directory *)ptr;
274 int to_copy = XEN_NUM_GREFS_PER_PAGE;
275
276 if (to_copy > grefs_left)
277 to_copy = grefs_left;
278
279 for (cur_gref = 0; cur_gref < to_copy; cur_gref++) {
280 phys_addr_t addr;
281
282 addr = xen_page_to_vaddr(buf->pages[cur_page]);
283 gnttab_set_map_op(&map_ops[cur_page], addr,
284 GNTMAP_host_map,
285 page_dir->gref[cur_gref],
286 buf->xb_dev->otherend_id);
287 cur_page++;
288 }
289
290 grefs_left -= to_copy;
291 ptr += PAGE_SIZE;
292 }
293 ret = gnttab_map_refs(map_ops, NULL, buf->pages, buf->num_pages);
294
295 /* Save handles even if error, so we can unmap. */
296 for (cur_page = 0; cur_page < buf->num_pages; cur_page++) {
297 if (likely(map_ops[cur_page].status == GNTST_okay)) {
298 buf->backend_map_handles[cur_page] =
299 map_ops[cur_page].handle;
300 } else {
301 buf->backend_map_handles[cur_page] =
302 INVALID_GRANT_HANDLE;
303 if (!ret)
304 ret = -ENXIO;
305 dev_err(&buf->xb_dev->dev,
306 "Failed to map page %d: %d\n",
307 cur_page, map_ops[cur_page].status);
308 }
309 }
310
311 if (ret) {
312 dev_err(&buf->xb_dev->dev,
313 "Failed to map grant references, ret %d", ret);
314 backend_unmap(buf);
315 }
316
317 kfree(map_ops);
318 return ret;
319}
320
321/*
322 * Fill page directory with grant references to the pages of the
323 * page directory itself.
324 *
325 * The grant references to the buffer pages are provided by the
326 * backend in this case.
327 *
328 * \param buf shared buffer.
329 */
330static void backend_fill_page_dir(struct xen_front_pgdir_shbuf *buf)
331{
332 struct xen_page_directory *page_dir;
333 unsigned char *ptr;
334 int i, num_pages_dir;
335
336 ptr = buf->directory;
337 num_pages_dir = get_num_pages_dir(buf);
338
339 /* Fill only grefs for the page directory itself. */
340 for (i = 0; i < num_pages_dir - 1; i++) {
341 page_dir = (struct xen_page_directory *)ptr;
342
343 page_dir->gref_dir_next_page = buf->grefs[i + 1];
344 ptr += PAGE_SIZE;
345 }
346 /* Last page must say there is no more pages. */
347 page_dir = (struct xen_page_directory *)ptr;
348 page_dir->gref_dir_next_page = XEN_GREF_LIST_END;
349}
350
351/*
352 * Fill page directory with grant references to the pages of the
353 * page directory and the buffer we share with the backend.
354 *
355 * \param buf shared buffer.
356 */
357static void guest_fill_page_dir(struct xen_front_pgdir_shbuf *buf)
358{
359 unsigned char *ptr;
360 int cur_gref, grefs_left, to_copy, i, num_pages_dir;
361
362 ptr = buf->directory;
363 num_pages_dir = get_num_pages_dir(buf);
364
365 /*
366 * While copying, skip grefs at start, they are for pages
367 * granted for the page directory itself.
368 */
369 cur_gref = num_pages_dir;
370 grefs_left = buf->num_pages;
371 for (i = 0; i < num_pages_dir; i++) {
372 struct xen_page_directory *page_dir =
373 (struct xen_page_directory *)ptr;
374
375 if (grefs_left <= XEN_NUM_GREFS_PER_PAGE) {
376 to_copy = grefs_left;
377 page_dir->gref_dir_next_page = XEN_GREF_LIST_END;
378 } else {
379 to_copy = XEN_NUM_GREFS_PER_PAGE;
380 page_dir->gref_dir_next_page = buf->grefs[i + 1];
381 }
382 memcpy(&page_dir->gref, &buf->grefs[cur_gref],
383 to_copy * sizeof(grant_ref_t));
384 ptr += PAGE_SIZE;
385 grefs_left -= to_copy;
386 cur_gref += to_copy;
387 }
388}
389
390/*
391 * Grant references to the frontend's buffer pages.
392 *
393 * These will be shared with the backend, so it can
394 * access the buffer's data.
395 *
396 * \param buf shared buffer.
397 * \return zero on success or a negative number on failure.
398 */
399static int guest_grant_refs_for_buffer(struct xen_front_pgdir_shbuf *buf,
400 grant_ref_t *priv_gref_head,
401 int gref_idx)
402{
403 int i, cur_ref, otherend_id;
404
405 otherend_id = buf->xb_dev->otherend_id;
406 for (i = 0; i < buf->num_pages; i++) {
407 cur_ref = gnttab_claim_grant_reference(priv_gref_head);
408 if (cur_ref < 0)
409 return cur_ref;
410
411 gnttab_grant_foreign_access_ref(cur_ref, otherend_id,
412 xen_page_to_gfn(buf->pages[i]),
413 0);
414 buf->grefs[gref_idx++] = cur_ref;
415 }
416 return 0;
417}
418
419/*
420 * Grant all the references needed to share the buffer.
421 *
422 * Grant references to the page directory pages and, if
423 * needed, also to the pages of the shared buffer data.
424 *
425 * \param buf shared buffer.
426 * \return zero on success or a negative number on failure.
427 */
428static int grant_references(struct xen_front_pgdir_shbuf *buf)
429{
430 grant_ref_t priv_gref_head;
431 int ret, i, j, cur_ref;
432 int otherend_id, num_pages_dir;
433
434 ret = gnttab_alloc_grant_references(buf->num_grefs, &priv_gref_head);
435 if (ret < 0) {
436 dev_err(&buf->xb_dev->dev,
437 "Cannot allocate grant references\n");
438 return ret;
439 }
440
441 otherend_id = buf->xb_dev->otherend_id;
442 j = 0;
443 num_pages_dir = get_num_pages_dir(buf);
444 for (i = 0; i < num_pages_dir; i++) {
445 unsigned long frame;
446
447 cur_ref = gnttab_claim_grant_reference(&priv_gref_head);
448 if (cur_ref < 0) {
449 ret = cur_ref;
450 goto out_free_refs;
451 }
452
453 frame = xen_page_to_gfn(virt_to_page(buf->directory +
454 PAGE_SIZE * i));
455 gnttab_grant_foreign_access_ref(cur_ref, otherend_id, frame, 0);
456 buf->grefs[j++] = cur_ref;
457 }
458
459 if (buf->ops->grant_refs_for_buffer) {
460 ret = buf->ops->grant_refs_for_buffer(buf, &priv_gref_head, j);
461 if (ret)
462 goto out_free_refs;
463 }
464
465 ret = 0;
466out_free_refs:
467 gnttab_free_grant_references(priv_gref_head);
468 return ret;
469}
470
471/*
472 * Allocate all required structures to mange shared buffer.
473 *
474 * \param buf shared buffer.
475 * \return zero on success or a negative number on failure.
476 */
477static int alloc_storage(struct xen_front_pgdir_shbuf *buf)
478{
479 buf->grefs = kzalloc_objs(*buf->grefs, buf->num_grefs);
480 if (!buf->grefs)
481 return -ENOMEM;
482
483 buf->directory = kcalloc(get_num_pages_dir(buf), PAGE_SIZE, GFP_KERNEL);
484 if (!buf->directory)
485 return -ENOMEM;
486
487 return 0;
488}
489
490/*
491 * For backend allocated buffers we don't need grant_refs_for_buffer
492 * as those grant references are allocated at backend side.
493 */
494static const struct xen_front_pgdir_shbuf_ops backend_ops = {
495 .calc_num_grefs = backend_calc_num_grefs,
496 .fill_page_dir = backend_fill_page_dir,
497 .map = backend_map,
498 .unmap = backend_unmap
499};
500
501/*
502 * For locally granted references we do not need to map/unmap
503 * the references.
504 */
505static const struct xen_front_pgdir_shbuf_ops local_ops = {
506 .calc_num_grefs = guest_calc_num_grefs,
507 .fill_page_dir = guest_fill_page_dir,
508 .grant_refs_for_buffer = guest_grant_refs_for_buffer,
509};
510
511/*
512 * Allocate a new instance of a shared buffer.
513 *
514 * \param cfg configuration to be used while allocating a new shared buffer.
515 * \return zero on success or a negative number on failure.
516 */
517int xen_front_pgdir_shbuf_alloc(struct xen_front_pgdir_shbuf_cfg *cfg)
518{
519 struct xen_front_pgdir_shbuf *buf = cfg->pgdir;
520 int ret;
521
522 if (cfg->be_alloc)
523 buf->ops = &backend_ops;
524 else
525 buf->ops = &local_ops;
526 buf->xb_dev = cfg->xb_dev;
527 buf->num_pages = cfg->num_pages;
528 buf->pages = cfg->pages;
529
530 buf->ops->calc_num_grefs(buf);
531
532 ret = alloc_storage(buf);
533 if (ret)
534 goto fail;
535
536 ret = grant_references(buf);
537 if (ret)
538 goto fail;
539
540 buf->ops->fill_page_dir(buf);
541
542 return 0;
543
544fail:
545 xen_front_pgdir_shbuf_free(buf);
546 return ret;
547}
548EXPORT_SYMBOL_GPL(xen_front_pgdir_shbuf_alloc);
549
550MODULE_DESCRIPTION("Xen frontend/backend page directory based "
551 "shared buffer handling");
552MODULE_AUTHOR("Oleksandr Andrushchenko");
553MODULE_LICENSE("GPL");