root/drivers/xen/xen-front-pgdir-shbuf.c

DEFINITIONS

1. xen_front_pgdir_shbuf_get_dir_start
2. xen_front_pgdir_shbuf_map
3. xen_front_pgdir_shbuf_unmap
4. xen_front_pgdir_shbuf_free
5. get_num_pages_dir
6. backend_calc_num_grefs
7. guest_calc_num_grefs
8. backend_unmap
9. backend_map
10. backend_fill_page_dir
11. guest_fill_page_dir
12. guest_grant_refs_for_buffer
13. grant_references
14. alloc_storage
15. xen_front_pgdir_shbuf_alloc

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