root/drivers/xen/swiotlb-xen.c

DEFINITIONS

1. xen_phys_to_bus
2. xen_bus_to_phys
3. xen_virt_to_bus
4. range_straddles_page_boundary
5. is_xen_swiotlb_buffer
6. xen_swiotlb_fixup
7. xen_set_nslabs
8. xen_swiotlb_error
9. xen_swiotlb_init
10. xen_swiotlb_alloc_coherent
11. xen_swiotlb_free_coherent
12. xen_swiotlb_map_page
13. xen_swiotlb_unmap_page
14. xen_swiotlb_sync_single_for_cpu
15. xen_swiotlb_sync_single_for_device
16. xen_swiotlb_unmap_sg
17. xen_swiotlb_map_sg
18. xen_swiotlb_sync_sg_for_cpu
19. xen_swiotlb_sync_sg_for_device
20. xen_swiotlb_dma_supported

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  *  Copyright 2010
   4  *  by Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
   5  *
   6  * This code provides a IOMMU for Xen PV guests with PCI passthrough.
   7  *
   8  * PV guests under Xen are running in an non-contiguous memory architecture.
   9  *
  10  * When PCI pass-through is utilized, this necessitates an IOMMU for
  11  * translating bus (DMA) to virtual and vice-versa and also providing a
  12  * mechanism to have contiguous pages for device drivers operations (say DMA
  13  * operations).
  14  *
  15  * Specifically, under Xen the Linux idea of pages is an illusion. It
  16  * assumes that pages start at zero and go up to the available memory. To
  17  * help with that, the Linux Xen MMU provides a lookup mechanism to
  18  * translate the page frame numbers (PFN) to machine frame numbers (MFN)
  19  * and vice-versa. The MFN are the "real" frame numbers. Furthermore
  20  * memory is not contiguous. Xen hypervisor stitches memory for guests
  21  * from different pools, which means there is no guarantee that PFN==MFN
  22  * and PFN+1==MFN+1. Lastly with Xen 4.0, pages (in debug mode) are
  23  * allocated in descending order (high to low), meaning the guest might
  24  * never get any MFN's under the 4GB mark.
  25  */
  26 
  27 #define pr_fmt(fmt) "xen:" KBUILD_MODNAME ": " fmt
  28 
  29 #include <linux/memblock.h>
  30 #include <linux/dma-direct.h>
  31 #include <linux/dma-noncoherent.h>
  32 #include <linux/export.h>
  33 #include <xen/swiotlb-xen.h>
  34 #include <xen/page.h>
  35 #include <xen/xen-ops.h>
  36 #include <xen/hvc-console.h>
  37 
  38 #include <asm/dma-mapping.h>
  39 #include <asm/xen/page-coherent.h>
  40 
  41 #include <trace/events/swiotlb.h>
  42 #define MAX_DMA_BITS 32
  43 /*
  44  * Used to do a quick range check in swiotlb_tbl_unmap_single and
  45  * swiotlb_tbl_sync_single_*, to see if the memory was in fact allocated by this
  46  * API.
  47  */
  48 
  49 static char *xen_io_tlb_start, *xen_io_tlb_end;
  50 static unsigned long xen_io_tlb_nslabs;
  51 /*
  52  * Quick lookup value of the bus address of the IOTLB.
  53  */
  54 
  55 static u64 start_dma_addr;
  56 
  57 /*
  58  * Both of these functions should avoid XEN_PFN_PHYS because phys_addr_t
  59  * can be 32bit when dma_addr_t is 64bit leading to a loss in
  60  * information if the shift is done before casting to 64bit.
  61  */
  62 static inline dma_addr_t xen_phys_to_bus(phys_addr_t paddr)
  63 {
  64         unsigned long bfn = pfn_to_bfn(XEN_PFN_DOWN(paddr));
  65         dma_addr_t dma = (dma_addr_t)bfn << XEN_PAGE_SHIFT;
  66 
  67         dma |= paddr & ~XEN_PAGE_MASK;
  68 
  69         return dma;
  70 }
  71 
  72 static inline phys_addr_t xen_bus_to_phys(dma_addr_t baddr)
  73 {
  74         unsigned long xen_pfn = bfn_to_pfn(XEN_PFN_DOWN(baddr));
  75         dma_addr_t dma = (dma_addr_t)xen_pfn << XEN_PAGE_SHIFT;
  76         phys_addr_t paddr = dma;
  77 
  78         paddr |= baddr & ~XEN_PAGE_MASK;
  79 
  80         return paddr;
  81 }
  82 
  83 static inline dma_addr_t xen_virt_to_bus(void *address)
  84 {
  85         return xen_phys_to_bus(virt_to_phys(address));
  86 }
  87 
  88 static inline int range_straddles_page_boundary(phys_addr_t p, size_t size)
  89 {
  90         unsigned long next_bfn, xen_pfn = XEN_PFN_DOWN(p);
  91         unsigned int i, nr_pages = XEN_PFN_UP(xen_offset_in_page(p) + size);
  92 
  93         next_bfn = pfn_to_bfn(xen_pfn);
  94 
  95         for (i = 1; i < nr_pages; i++)
  96                 if (pfn_to_bfn(++xen_pfn) != ++next_bfn)
  97                         return 1;
  98 
  99         return 0;
 100 }
 101 
 102 static int is_xen_swiotlb_buffer(dma_addr_t dma_addr)
 103 {
 104         unsigned long bfn = XEN_PFN_DOWN(dma_addr);
 105         unsigned long xen_pfn = bfn_to_local_pfn(bfn);
 106         phys_addr_t paddr = XEN_PFN_PHYS(xen_pfn);
 107 
 108         /* If the address is outside our domain, it CAN
 109          * have the same virtual address as another address
 110          * in our domain. Therefore _only_ check address within our domain.
 111          */
 112         if (pfn_valid(PFN_DOWN(paddr))) {
 113                 return paddr >= virt_to_phys(xen_io_tlb_start) &&
 114                        paddr < virt_to_phys(xen_io_tlb_end);
 115         }
 116         return 0;
 117 }
 118 
 119 static int
 120 xen_swiotlb_fixup(void *buf, size_t size, unsigned long nslabs)
 121 {
 122         int i, rc;
 123         int dma_bits;
 124         dma_addr_t dma_handle;
 125         phys_addr_t p = virt_to_phys(buf);
 126 
 127         dma_bits = get_order(IO_TLB_SEGSIZE << IO_TLB_SHIFT) + PAGE_SHIFT;
 128 
 129         i = 0;
 130         do {
 131                 int slabs = min(nslabs - i, (unsigned long)IO_TLB_SEGSIZE);
 132 
 133                 do {
 134                         rc = xen_create_contiguous_region(
 135                                 p + (i << IO_TLB_SHIFT),
 136                                 get_order(slabs << IO_TLB_SHIFT),
 137                                 dma_bits, &dma_handle);
 138                 } while (rc && dma_bits++ < MAX_DMA_BITS);
 139                 if (rc)
 140                         return rc;
 141 
 142                 i += slabs;
 143         } while (i < nslabs);
 144         return 0;
 145 }
 146 static unsigned long xen_set_nslabs(unsigned long nr_tbl)
 147 {
 148         if (!nr_tbl) {
 149                 xen_io_tlb_nslabs = (64 * 1024 * 1024 >> IO_TLB_SHIFT);
 150                 xen_io_tlb_nslabs = ALIGN(xen_io_tlb_nslabs, IO_TLB_SEGSIZE);
 151         } else
 152                 xen_io_tlb_nslabs = nr_tbl;
 153 
 154         return xen_io_tlb_nslabs << IO_TLB_SHIFT;
 155 }
 156 
 157 enum xen_swiotlb_err {
 158         XEN_SWIOTLB_UNKNOWN = 0,
 159         XEN_SWIOTLB_ENOMEM,
 160         XEN_SWIOTLB_EFIXUP
 161 };
 162 
 163 static const char *xen_swiotlb_error(enum xen_swiotlb_err err)
 164 {
 165         switch (err) {
 166         case XEN_SWIOTLB_ENOMEM:
 167                 return "Cannot allocate Xen-SWIOTLB buffer\n";
 168         case XEN_SWIOTLB_EFIXUP:
 169                 return "Failed to get contiguous memory for DMA from Xen!\n"\
 170                     "You either: don't have the permissions, do not have"\
 171                     " enough free memory under 4GB, or the hypervisor memory"\
 172                     " is too fragmented!";
 173         default:
 174                 break;
 175         }
 176         return "";
 177 }
 178 int __ref xen_swiotlb_init(int verbose, bool early)
 179 {
 180         unsigned long bytes, order;
 181         int rc = -ENOMEM;
 182         enum xen_swiotlb_err m_ret = XEN_SWIOTLB_UNKNOWN;
 183         unsigned int repeat = 3;
 184 
 185         xen_io_tlb_nslabs = swiotlb_nr_tbl();
 186 retry:
 187         bytes = xen_set_nslabs(xen_io_tlb_nslabs);
 188         order = get_order(xen_io_tlb_nslabs << IO_TLB_SHIFT);
 189 
 190         /*
 191          * IO TLB memory already allocated. Just use it.
 192          */
 193         if (io_tlb_start != 0) {
 194                 xen_io_tlb_start = phys_to_virt(io_tlb_start);
 195                 goto end;
 196         }
 197 
 198         /*
 199          * Get IO TLB memory from any location.
 200          */
 201         if (early) {
 202                 xen_io_tlb_start = memblock_alloc(PAGE_ALIGN(bytes),
 203                                                   PAGE_SIZE);
 204                 if (!xen_io_tlb_start)
 205                         panic("%s: Failed to allocate %lu bytes align=0x%lx\n",
 206                               __func__, PAGE_ALIGN(bytes), PAGE_SIZE);
 207         } else {
 208 #define SLABS_PER_PAGE (1 << (PAGE_SHIFT - IO_TLB_SHIFT))
 209 #define IO_TLB_MIN_SLABS ((1<<20) >> IO_TLB_SHIFT)
 210                 while ((SLABS_PER_PAGE << order) > IO_TLB_MIN_SLABS) {
 211                         xen_io_tlb_start = (void *)xen_get_swiotlb_free_pages(order);
 212                         if (xen_io_tlb_start)
 213                                 break;
 214                         order--;
 215                 }
 216                 if (order != get_order(bytes)) {
 217                         pr_warn("Warning: only able to allocate %ld MB for software IO TLB\n",
 218                                 (PAGE_SIZE << order) >> 20);
 219                         xen_io_tlb_nslabs = SLABS_PER_PAGE << order;
 220                         bytes = xen_io_tlb_nslabs << IO_TLB_SHIFT;
 221                 }
 222         }
 223         if (!xen_io_tlb_start) {
 224                 m_ret = XEN_SWIOTLB_ENOMEM;
 225                 goto error;
 226         }
 227         /*
 228          * And replace that memory with pages under 4GB.
 229          */
 230         rc = xen_swiotlb_fixup(xen_io_tlb_start,
 231                                bytes,
 232                                xen_io_tlb_nslabs);
 233         if (rc) {
 234                 if (early)
 235                         memblock_free(__pa(xen_io_tlb_start),
 236                                       PAGE_ALIGN(bytes));
 237                 else {
 238                         free_pages((unsigned long)xen_io_tlb_start, order);
 239                         xen_io_tlb_start = NULL;
 240                 }
 241                 m_ret = XEN_SWIOTLB_EFIXUP;
 242                 goto error;
 243         }
 244         start_dma_addr = xen_virt_to_bus(xen_io_tlb_start);
 245         if (early) {
 246                 if (swiotlb_init_with_tbl(xen_io_tlb_start, xen_io_tlb_nslabs,
 247                          verbose))
 248                         panic("Cannot allocate SWIOTLB buffer");
 249                 rc = 0;
 250         } else
 251                 rc = swiotlb_late_init_with_tbl(xen_io_tlb_start, xen_io_tlb_nslabs);
 252 
 253 end:
 254         xen_io_tlb_end = xen_io_tlb_start + bytes;
 255         if (!rc)
 256                 swiotlb_set_max_segment(PAGE_SIZE);
 257 
 258         return rc;
 259 error:
 260         if (repeat--) {
 261                 xen_io_tlb_nslabs = max(1024UL, /* Min is 2MB */
 262                                         (xen_io_tlb_nslabs >> 1));
 263                 pr_info("Lowering to %luMB\n",
 264                         (xen_io_tlb_nslabs << IO_TLB_SHIFT) >> 20);
 265                 goto retry;
 266         }
 267         pr_err("%s (rc:%d)\n", xen_swiotlb_error(m_ret), rc);
 268         if (early)
 269                 panic("%s (rc:%d)", xen_swiotlb_error(m_ret), rc);
 270         else
 271                 free_pages((unsigned long)xen_io_tlb_start, order);
 272         return rc;
 273 }
 274 
 275 static void *
 276 xen_swiotlb_alloc_coherent(struct device *hwdev, size_t size,
 277                            dma_addr_t *dma_handle, gfp_t flags,
 278                            unsigned long attrs)
 279 {
 280         void *ret;
 281         int order = get_order(size);
 282         u64 dma_mask = DMA_BIT_MASK(32);
 283         phys_addr_t phys;
 284         dma_addr_t dev_addr;
 285 
 286         /*
 287         * Ignore region specifiers - the kernel's ideas of
 288         * pseudo-phys memory layout has nothing to do with the
 289         * machine physical layout.  We can't allocate highmem
 290         * because we can't return a pointer to it.
 291         */
 292         flags &= ~(__GFP_DMA | __GFP_HIGHMEM);
 293 
 294         /* Convert the size to actually allocated. */
 295         size = 1UL << (order + XEN_PAGE_SHIFT);
 296 
 297         /* On ARM this function returns an ioremap'ped virtual address for
 298          * which virt_to_phys doesn't return the corresponding physical
 299          * address. In fact on ARM virt_to_phys only works for kernel direct
 300          * mapped RAM memory. Also see comment below.
 301          */
 302         ret = xen_alloc_coherent_pages(hwdev, size, dma_handle, flags, attrs);
 303 
 304         if (!ret)
 305                 return ret;
 306 
 307         if (hwdev && hwdev->coherent_dma_mask)
 308                 dma_mask = hwdev->coherent_dma_mask;
 309 
 310         /* At this point dma_handle is the physical address, next we are
 311          * going to set it to the machine address.
 312          * Do not use virt_to_phys(ret) because on ARM it doesn't correspond
 313          * to *dma_handle. */
 314         phys = *dma_handle;
 315         dev_addr = xen_phys_to_bus(phys);
 316         if (((dev_addr + size - 1 <= dma_mask)) &&
 317             !range_straddles_page_boundary(phys, size))
 318                 *dma_handle = dev_addr;
 319         else {
 320                 if (xen_create_contiguous_region(phys, order,
 321                                                  fls64(dma_mask), dma_handle) != 0) {
 322                         xen_free_coherent_pages(hwdev, size, ret, (dma_addr_t)phys, attrs);
 323                         return NULL;
 324                 }
 325                 SetPageXenRemapped(virt_to_page(ret));
 326         }
 327         memset(ret, 0, size);
 328         return ret;
 329 }
 330 
 331 static void
 332 xen_swiotlb_free_coherent(struct device *hwdev, size_t size, void *vaddr,
 333                           dma_addr_t dev_addr, unsigned long attrs)
 334 {
 335         int order = get_order(size);
 336         phys_addr_t phys;
 337         u64 dma_mask = DMA_BIT_MASK(32);
 338 
 339         if (hwdev && hwdev->coherent_dma_mask)
 340                 dma_mask = hwdev->coherent_dma_mask;
 341 
 342         /* do not use virt_to_phys because on ARM it doesn't return you the
 343          * physical address */
 344         phys = xen_bus_to_phys(dev_addr);
 345 
 346         /* Convert the size to actually allocated. */
 347         size = 1UL << (order + XEN_PAGE_SHIFT);
 348 
 349         if (!WARN_ON((dev_addr + size - 1 > dma_mask) ||
 350                      range_straddles_page_boundary(phys, size)) &&
 351             TestClearPageXenRemapped(virt_to_page(vaddr)))
 352                 xen_destroy_contiguous_region(phys, order);
 353 
 354         xen_free_coherent_pages(hwdev, size, vaddr, (dma_addr_t)phys, attrs);
 355 }
 356 
 357 /*
 358  * Map a single buffer of the indicated size for DMA in streaming mode.  The
 359  * physical address to use is returned.
 360  *
 361  * Once the device is given the dma address, the device owns this memory until
 362  * either xen_swiotlb_unmap_page or xen_swiotlb_dma_sync_single is performed.
 363  */
 364 static dma_addr_t xen_swiotlb_map_page(struct device *dev, struct page *page,
 365                                 unsigned long offset, size_t size,
 366                                 enum dma_data_direction dir,
 367                                 unsigned long attrs)
 368 {
 369         phys_addr_t map, phys = page_to_phys(page) + offset;
 370         dma_addr_t dev_addr = xen_phys_to_bus(phys);
 371 
 372         BUG_ON(dir == DMA_NONE);
 373         /*
 374          * If the address happens to be in the device's DMA window,
 375          * we can safely return the device addr and not worry about bounce
 376          * buffering it.
 377          */
 378         if (dma_capable(dev, dev_addr, size) &&
 379             !range_straddles_page_boundary(phys, size) &&
 380                 !xen_arch_need_swiotlb(dev, phys, dev_addr) &&
 381                 swiotlb_force != SWIOTLB_FORCE)
 382                 goto done;
 383 
 384         /*
 385          * Oh well, have to allocate and map a bounce buffer.
 386          */
 387         trace_swiotlb_bounced(dev, dev_addr, size, swiotlb_force);
 388 
 389         map = swiotlb_tbl_map_single(dev, start_dma_addr, phys,
 390                                      size, size, dir, attrs);
 391         if (map == (phys_addr_t)DMA_MAPPING_ERROR)
 392                 return DMA_MAPPING_ERROR;
 393 
 394         phys = map;
 395         dev_addr = xen_phys_to_bus(map);
 396 
 397         /*
 398          * Ensure that the address returned is DMA'ble
 399          */
 400         if (unlikely(!dma_capable(dev, dev_addr, size))) {
 401                 swiotlb_tbl_unmap_single(dev, map, size, size, dir,
 402                                 attrs | DMA_ATTR_SKIP_CPU_SYNC);
 403                 return DMA_MAPPING_ERROR;
 404         }
 405 
 406 done:
 407         if (!dev_is_dma_coherent(dev) && !(attrs & DMA_ATTR_SKIP_CPU_SYNC))
 408                 xen_dma_sync_for_device(dev, dev_addr, phys, size, dir);
 409         return dev_addr;
 410 }
 411 
 412 /*
 413  * Unmap a single streaming mode DMA translation.  The dma_addr and size must
 414  * match what was provided for in a previous xen_swiotlb_map_page call.  All
 415  * other usages are undefined.
 416  *
 417  * After this call, reads by the cpu to the buffer are guaranteed to see
 418  * whatever the device wrote there.
 419  */
 420 static void xen_swiotlb_unmap_page(struct device *hwdev, dma_addr_t dev_addr,
 421                 size_t size, enum dma_data_direction dir, unsigned long attrs)
 422 {
 423         phys_addr_t paddr = xen_bus_to_phys(dev_addr);
 424 
 425         BUG_ON(dir == DMA_NONE);
 426 
 427         if (!dev_is_dma_coherent(hwdev) && !(attrs & DMA_ATTR_SKIP_CPU_SYNC))
 428                 xen_dma_sync_for_cpu(hwdev, dev_addr, paddr, size, dir);
 429 
 430         /* NOTE: We use dev_addr here, not paddr! */
 431         if (is_xen_swiotlb_buffer(dev_addr))
 432                 swiotlb_tbl_unmap_single(hwdev, paddr, size, size, dir, attrs);
 433 }
 434 
 435 static void
 436 xen_swiotlb_sync_single_for_cpu(struct device *dev, dma_addr_t dma_addr,
 437                 size_t size, enum dma_data_direction dir)
 438 {
 439         phys_addr_t paddr = xen_bus_to_phys(dma_addr);
 440 
 441         if (!dev_is_dma_coherent(dev))
 442                 xen_dma_sync_for_cpu(dev, dma_addr, paddr, size, dir);
 443 
 444         if (is_xen_swiotlb_buffer(dma_addr))
 445                 swiotlb_tbl_sync_single(dev, paddr, size, dir, SYNC_FOR_CPU);
 446 }
 447 
 448 static void
 449 xen_swiotlb_sync_single_for_device(struct device *dev, dma_addr_t dma_addr,
 450                 size_t size, enum dma_data_direction dir)
 451 {
 452         phys_addr_t paddr = xen_bus_to_phys(dma_addr);
 453 
 454         if (is_xen_swiotlb_buffer(dma_addr))
 455                 swiotlb_tbl_sync_single(dev, paddr, size, dir, SYNC_FOR_DEVICE);
 456 
 457         if (!dev_is_dma_coherent(dev))
 458                 xen_dma_sync_for_device(dev, dma_addr, paddr, size, dir);
 459 }
 460 
 461 /*
 462  * Unmap a set of streaming mode DMA translations.  Again, cpu read rules
 463  * concerning calls here are the same as for swiotlb_unmap_page() above.
 464  */
 465 static void
 466 xen_swiotlb_unmap_sg(struct device *hwdev, struct scatterlist *sgl, int nelems,
 467                 enum dma_data_direction dir, unsigned long attrs)
 468 {
 469         struct scatterlist *sg;
 470         int i;
 471 
 472         BUG_ON(dir == DMA_NONE);
 473 
 474         for_each_sg(sgl, sg, nelems, i)
 475                 xen_swiotlb_unmap_page(hwdev, sg->dma_address, sg_dma_len(sg),
 476                                 dir, attrs);
 477 
 478 }
 479 
 480 static int
 481 xen_swiotlb_map_sg(struct device *dev, struct scatterlist *sgl, int nelems,
 482                 enum dma_data_direction dir, unsigned long attrs)
 483 {
 484         struct scatterlist *sg;
 485         int i;
 486 
 487         BUG_ON(dir == DMA_NONE);
 488 
 489         for_each_sg(sgl, sg, nelems, i) {
 490                 sg->dma_address = xen_swiotlb_map_page(dev, sg_page(sg),
 491                                 sg->offset, sg->length, dir, attrs);
 492                 if (sg->dma_address == DMA_MAPPING_ERROR)
 493                         goto out_unmap;
 494                 sg_dma_len(sg) = sg->length;
 495         }
 496 
 497         return nelems;
 498 out_unmap:
 499         xen_swiotlb_unmap_sg(dev, sgl, i, dir, attrs | DMA_ATTR_SKIP_CPU_SYNC);
 500         sg_dma_len(sgl) = 0;
 501         return 0;
 502 }
 503 
 504 static void
 505 xen_swiotlb_sync_sg_for_cpu(struct device *dev, struct scatterlist *sgl,
 506                             int nelems, enum dma_data_direction dir)
 507 {
 508         struct scatterlist *sg;
 509         int i;
 510 
 511         for_each_sg(sgl, sg, nelems, i) {
 512                 xen_swiotlb_sync_single_for_cpu(dev, sg->dma_address,
 513                                 sg->length, dir);
 514         }
 515 }
 516 
 517 static void
 518 xen_swiotlb_sync_sg_for_device(struct device *dev, struct scatterlist *sgl,
 519                                int nelems, enum dma_data_direction dir)
 520 {
 521         struct scatterlist *sg;
 522         int i;
 523 
 524         for_each_sg(sgl, sg, nelems, i) {
 525                 xen_swiotlb_sync_single_for_device(dev, sg->dma_address,
 526                                 sg->length, dir);
 527         }
 528 }
 529 
 530 /*
 531  * Return whether the given device DMA address mask can be supported
 532  * properly.  For example, if your device can only drive the low 24-bits
 533  * during bus mastering, then you would pass 0x00ffffff as the mask to
 534  * this function.
 535  */
 536 static int
 537 xen_swiotlb_dma_supported(struct device *hwdev, u64 mask)
 538 {
 539         return xen_virt_to_bus(xen_io_tlb_end - 1) <= mask;
 540 }
 541 
 542 const struct dma_map_ops xen_swiotlb_dma_ops = {
 543         .alloc = xen_swiotlb_alloc_coherent,
 544         .free = xen_swiotlb_free_coherent,
 545         .sync_single_for_cpu = xen_swiotlb_sync_single_for_cpu,
 546         .sync_single_for_device = xen_swiotlb_sync_single_for_device,
 547         .sync_sg_for_cpu = xen_swiotlb_sync_sg_for_cpu,
 548         .sync_sg_for_device = xen_swiotlb_sync_sg_for_device,
 549         .map_sg = xen_swiotlb_map_sg,
 550         .unmap_sg = xen_swiotlb_unmap_sg,
 551         .map_page = xen_swiotlb_map_page,
 552         .unmap_page = xen_swiotlb_unmap_page,
 553         .dma_supported = xen_swiotlb_dma_supported,
 554         .mmap = dma_common_mmap,
 555         .get_sgtable = dma_common_get_sgtable,
 556 };