drivers/xen/swiotlb-xen.c - kernel/msm-4.19 - Gitiles

 /*
  *  Copyright 2010
  *  by Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
  *
  * This code provides a IOMMU for Xen PV guests with PCI passthrough.
  *
  * This program is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License v2.0 as published by
  * the Free Software Foundation
  *
  * This program is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  * GNU General Public License for more details.
  *
  * PV guests under Xen are running in an non-contiguous memory architecture.
  *
  * When PCI pass-through is utilized, this necessitates an IOMMU for
  * translating bus (DMA) to virtual and vice-versa and also providing a
  * mechanism to have contiguous pages for device drivers operations (say DMA
  * operations).
  *
  * Specifically, under Xen the Linux idea of pages is an illusion. It
  * assumes that pages start at zero and go up to the available memory. To
  * help with that, the Linux Xen MMU provides a lookup mechanism to
  * translate the page frame numbers (PFN) to machine frame numbers (MFN)
  * and vice-versa. The MFN are the "real" frame numbers. Furthermore
  * memory is not contiguous. Xen hypervisor stitches memory for guests
  * from different pools, which means there is no guarantee that PFN==MFN
  * and PFN+1==MFN+1. Lastly with Xen 4.0, pages (in debug mode) are
  * allocated in descending order (high to low), meaning the guest might
  * never get any MFN's under the 4GB mark.
  *
  */

 #define pr_fmt(fmt) "xen:" KBUILD_MODNAME ": " fmt

 #include <linux/bootmem.h>
 #include <linux/dma-mapping.h>
 #include <linux/export.h>
 #include <xen/swiotlb-xen.h>
 #include <xen/page.h>
 #include <xen/xen-ops.h>
 #include <xen/hvc-console.h>

 #include <asm/dma-mapping.h>
 #include <asm/xen/page-coherent.h>

 #include <trace/events/swiotlb.h>
 /*
  * Used to do a quick range check in swiotlb_tbl_unmap_single and
  * swiotlb_tbl_sync_single_*, to see if the memory was in fact allocated by this
  * API.
  */

 #ifndef CONFIG_X86
 static unsigned long dma_alloc_coherent_mask(struct device *dev,
 					    gfp_t gfp)
 {
 	unsigned long dma_mask = 0;

 	dma_mask = dev->coherent_dma_mask;
 	if (!dma_mask)
 		dma_mask = (gfp & GFP_DMA) ? DMA_BIT_MASK(24) : DMA_BIT_MASK(32);

 	return dma_mask;
 }
 #endif

 static char *xen_io_tlb_start, *xen_io_tlb_end;
 static unsigned long xen_io_tlb_nslabs;
 /*
  * Quick lookup value of the bus address of the IOTLB.
  */

 static u64 start_dma_addr;

 /*
  * Both of these functions should avoid XEN_PFN_PHYS because phys_addr_t
  * can be 32bit when dma_addr_t is 64bit leading to a loss in
  * information if the shift is done before casting to 64bit.
  */
 static inline dma_addr_t xen_phys_to_bus(phys_addr_t paddr)
 {
 	unsigned long bfn = pfn_to_bfn(XEN_PFN_DOWN(paddr));
 	dma_addr_t dma = (dma_addr_t)bfn << XEN_PAGE_SHIFT;

 	dma |= paddr & ~XEN_PAGE_MASK;

 	return dma;
 }

 static inline phys_addr_t xen_bus_to_phys(dma_addr_t baddr)
 {
 	unsigned long xen_pfn = bfn_to_pfn(XEN_PFN_DOWN(baddr));
 	dma_addr_t dma = (dma_addr_t)xen_pfn << XEN_PAGE_SHIFT;
 	phys_addr_t paddr = dma;

 	paddr |= baddr & ~XEN_PAGE_MASK;

 	return paddr;
 }

 static inline dma_addr_t xen_virt_to_bus(void *address)
 {
 	return xen_phys_to_bus(virt_to_phys(address));
 }

 static int check_pages_physically_contiguous(unsigned long xen_pfn,
 					     unsigned int offset,
 					     size_t length)
 {
 	unsigned long next_bfn;
 	int i;
 	int nr_pages;

 	next_bfn = pfn_to_bfn(xen_pfn);
 	nr_pages = (offset + length + XEN_PAGE_SIZE-1) >> XEN_PAGE_SHIFT;

 	for (i = 1; i < nr_pages; i++) {
 		if (pfn_to_bfn(++xen_pfn) != ++next_bfn)
 			return 0;
 	}
 	return 1;
 }

 static inline int range_straddles_page_boundary(phys_addr_t p, size_t size)
 {
 	unsigned long xen_pfn = XEN_PFN_DOWN(p);
 	unsigned int offset = p & ~XEN_PAGE_MASK;

 	if (offset + size <= XEN_PAGE_SIZE)
 		return 0;
 	if (check_pages_physically_contiguous(xen_pfn, offset, size))
 		return 0;
 	return 1;
 }

 static int is_xen_swiotlb_buffer(dma_addr_t dma_addr)
 {
 	unsigned long bfn = XEN_PFN_DOWN(dma_addr);
 	unsigned long xen_pfn = bfn_to_local_pfn(bfn);
 	phys_addr_t paddr = XEN_PFN_PHYS(xen_pfn);

 	/* If the address is outside our domain, it CAN
 	 * have the same virtual address as another address
 	 * in our domain. Therefore _only_ check address within our domain.
 	 */
 	if (pfn_valid(PFN_DOWN(paddr))) {
 		return paddr >= virt_to_phys(xen_io_tlb_start) &&
 		       paddr < virt_to_phys(xen_io_tlb_end);
 	}
 	return 0;
 }

 static int max_dma_bits = 32;

 static int
 xen_swiotlb_fixup(void *buf, size_t size, unsigned long nslabs)
 {
 	int i, rc;
 	int dma_bits;
 	dma_addr_t dma_handle;
 	phys_addr_t p = virt_to_phys(buf);

 	dma_bits = get_order(IO_TLB_SEGSIZE << IO_TLB_SHIFT) + PAGE_SHIFT;

 	i = 0;
 	do {
 		int slabs = min(nslabs - i, (unsigned long)IO_TLB_SEGSIZE);

 		do {
 			rc = xen_create_contiguous_region(
 				p + (i << IO_TLB_SHIFT),
 				get_order(slabs << IO_TLB_SHIFT),
 				dma_bits, &dma_handle);
 		} while (rc && dma_bits++ < max_dma_bits);
 		if (rc)
 			return rc;

 		i += slabs;
 	} while (i < nslabs);
 	return 0;
 }
 static unsigned long xen_set_nslabs(unsigned long nr_tbl)
 {
 	if (!nr_tbl) {
 		xen_io_tlb_nslabs = (64 * 1024 * 1024 >> IO_TLB_SHIFT);
 		xen_io_tlb_nslabs = ALIGN(xen_io_tlb_nslabs, IO_TLB_SEGSIZE);
 	} else
 		xen_io_tlb_nslabs = nr_tbl;

 	return xen_io_tlb_nslabs << IO_TLB_SHIFT;
 }

 enum xen_swiotlb_err {
 	XEN_SWIOTLB_UNKNOWN = 0,
 	XEN_SWIOTLB_ENOMEM,
 	XEN_SWIOTLB_EFIXUP
 };

 static const char *xen_swiotlb_error(enum xen_swiotlb_err err)
 {
 	switch (err) {
 	case XEN_SWIOTLB_ENOMEM:
 		return "Cannot allocate Xen-SWIOTLB buffer\n";
 	case XEN_SWIOTLB_EFIXUP:
 		return "Failed to get contiguous memory for DMA from Xen!\n"\
 		    "You either: don't have the permissions, do not have"\
 		    " enough free memory under 4GB, or the hypervisor memory"\
 		    " is too fragmented!";
 	default:
 		break;
 	}
 	return "";
 }
 int __ref xen_swiotlb_init(int verbose, bool early)
 {
 	unsigned long bytes, order;
 	int rc = -ENOMEM;
 	enum xen_swiotlb_err m_ret = XEN_SWIOTLB_UNKNOWN;
 	unsigned int repeat = 3;

 	xen_io_tlb_nslabs = swiotlb_nr_tbl();
 retry:
 	bytes = xen_set_nslabs(xen_io_tlb_nslabs);
 	order = get_order(xen_io_tlb_nslabs << IO_TLB_SHIFT);
 	/*
 	 * Get IO TLB memory from any location.
 	 */
 	if (early)
 		xen_io_tlb_start = alloc_bootmem_pages(PAGE_ALIGN(bytes));
 	else {
 #define SLABS_PER_PAGE (1 << (PAGE_SHIFT - IO_TLB_SHIFT))
 #define IO_TLB_MIN_SLABS ((1<<20) >> IO_TLB_SHIFT)
 		while ((SLABS_PER_PAGE << order) > IO_TLB_MIN_SLABS) {
 			xen_io_tlb_start = (void *)xen_get_swiotlb_free_pages(order);
 			if (xen_io_tlb_start)
 				break;
 			order--;
 		}
 		if (order != get_order(bytes)) {
 			pr_warn("Warning: only able to allocate %ld MB for software IO TLB\n",
 				(PAGE_SIZE << order) >> 20);
 			xen_io_tlb_nslabs = SLABS_PER_PAGE << order;
 			bytes = xen_io_tlb_nslabs << IO_TLB_SHIFT;
 		}
 	}
 	if (!xen_io_tlb_start) {
 		m_ret = XEN_SWIOTLB_ENOMEM;
 		goto error;
 	}
 	xen_io_tlb_end = xen_io_tlb_start + bytes;
 	/*
 	 * And replace that memory with pages under 4GB.
 	 */
 	rc = xen_swiotlb_fixup(xen_io_tlb_start,
 			       bytes,
 			       xen_io_tlb_nslabs);
 	if (rc) {
 		if (early)
 			free_bootmem(__pa(xen_io_tlb_start), PAGE_ALIGN(bytes));
 		else {
 			free_pages((unsigned long)xen_io_tlb_start, order);
 			xen_io_tlb_start = NULL;
 		}
 		m_ret = XEN_SWIOTLB_EFIXUP;
 		goto error;
 	}
 	start_dma_addr = xen_virt_to_bus(xen_io_tlb_start);
 	if (early) {
 		if (swiotlb_init_with_tbl(xen_io_tlb_start, xen_io_tlb_nslabs,
 			 verbose))
 			panic("Cannot allocate SWIOTLB buffer");
 		rc = 0;
 	} else
 		rc = swiotlb_late_init_with_tbl(xen_io_tlb_start, xen_io_tlb_nslabs);
 	return rc;
 error:
 	if (repeat--) {
 		xen_io_tlb_nslabs = max(1024UL, /* Min is 2MB */
 					(xen_io_tlb_nslabs >> 1));
 		pr_info("Lowering to %luMB\n",
 			(xen_io_tlb_nslabs << IO_TLB_SHIFT) >> 20);
 		goto retry;
 	}
 	pr_err("%s (rc:%d)\n", xen_swiotlb_error(m_ret), rc);
 	if (early)
 		panic("%s (rc:%d)", xen_swiotlb_error(m_ret), rc);
 	else
 		free_pages((unsigned long)xen_io_tlb_start, order);
 	return rc;
 }
 void *
 xen_swiotlb_alloc_coherent(struct device *hwdev, size_t size,
 			   dma_addr_t *dma_handle, gfp_t flags,
 			   unsigned long attrs)
 {
 	void *ret;
 	int order = get_order(size);
 	u64 dma_mask = DMA_BIT_MASK(32);
 	phys_addr_t phys;
 	dma_addr_t dev_addr;

 	/*
 	* Ignore region specifiers - the kernel's ideas of
 	* pseudo-phys memory layout has nothing to do with the
 	* machine physical layout.  We can't allocate highmem
 	* because we can't return a pointer to it.
 	*/
 	flags &= ~(__GFP_DMA | __GFP_HIGHMEM);

 	/* On ARM this function returns an ioremap'ped virtual address for
 	 * which virt_to_phys doesn't return the corresponding physical
 	 * address. In fact on ARM virt_to_phys only works for kernel direct
 	 * mapped RAM memory. Also see comment below.
 	 */
 	ret = xen_alloc_coherent_pages(hwdev, size, dma_handle, flags, attrs);

 	if (!ret)
 		return ret;

 	if (hwdev && hwdev->coherent_dma_mask)
 		dma_mask = dma_alloc_coherent_mask(hwdev, flags);

 	/* At this point dma_handle is the physical address, next we are
 	 * going to set it to the machine address.
 	 * Do not use virt_to_phys(ret) because on ARM it doesn't correspond
 	 * to *dma_handle. */
 	phys = *dma_handle;
 	dev_addr = xen_phys_to_bus(phys);
 	if (((dev_addr + size - 1 <= dma_mask)) &&
 	    !range_straddles_page_boundary(phys, size))
 		*dma_handle = dev_addr;
 	else {
 		if (xen_create_contiguous_region(phys, order,
 						 fls64(dma_mask), dma_handle) != 0) {
 			xen_free_coherent_pages(hwdev, size, ret, (dma_addr_t)phys, attrs);
 			return NULL;
 		}
 	}
 	memset(ret, 0, size);
 	return ret;
 }
 EXPORT_SYMBOL_GPL(xen_swiotlb_alloc_coherent);

 void
 xen_swiotlb_free_coherent(struct device *hwdev, size_t size, void *vaddr,
 			  dma_addr_t dev_addr, unsigned long attrs)
 {
 	int order = get_order(size);
 	phys_addr_t phys;
 	u64 dma_mask = DMA_BIT_MASK(32);

 	if (hwdev && hwdev->coherent_dma_mask)
 		dma_mask = hwdev->coherent_dma_mask;

 	/* do not use virt_to_phys because on ARM it doesn't return you the
 	 * physical address */
 	phys = xen_bus_to_phys(dev_addr);

 	if (((dev_addr + size - 1 > dma_mask)) ||
 	    range_straddles_page_boundary(phys, size))
 		xen_destroy_contiguous_region(phys, order);

 	xen_free_coherent_pages(hwdev, size, vaddr, (dma_addr_t)phys, attrs);
 }
 EXPORT_SYMBOL_GPL(xen_swiotlb_free_coherent);


 /*
  * Map a single buffer of the indicated size for DMA in streaming mode.  The
  * physical address to use is returned.
  *
  * Once the device is given the dma address, the device owns this memory until
  * either xen_swiotlb_unmap_page or xen_swiotlb_dma_sync_single is performed.
  */
 dma_addr_t xen_swiotlb_map_page(struct device *dev, struct page *page,
 				unsigned long offset, size_t size,
 				enum dma_data_direction dir,
 				unsigned long attrs)
 {
 	phys_addr_t map, phys = page_to_phys(page) + offset;
 	dma_addr_t dev_addr = xen_phys_to_bus(phys);

 	BUG_ON(dir == DMA_NONE);
 	/*
 	 * If the address happens to be in the device's DMA window,
 	 * we can safely return the device addr and not worry about bounce
 	 * buffering it.
 	 */
 	if (dma_capable(dev, dev_addr, size) &&
 	    !range_straddles_page_boundary(phys, size) &&
 		!xen_arch_need_swiotlb(dev, phys, dev_addr) &&
 		!swiotlb_force) {
 		/* we are not interested in the dma_addr returned by
 		 * xen_dma_map_page, only in the potential cache flushes executed
 		 * by the function. */
 		xen_dma_map_page(dev, page, dev_addr, offset, size, dir, attrs);
 		return dev_addr;
 	}

 	/*
 	 * Oh well, have to allocate and map a bounce buffer.
 	 */
 	trace_swiotlb_bounced(dev, dev_addr, size, swiotlb_force);

 	map = swiotlb_tbl_map_single(dev, start_dma_addr, phys, size, dir,
 				     attrs);
 	if (map == SWIOTLB_MAP_ERROR)
 		return DMA_ERROR_CODE;

 	xen_dma_map_page(dev, pfn_to_page(map >> PAGE_SHIFT),
 					dev_addr, map & ~PAGE_MASK, size, dir, attrs);
 	dev_addr = xen_phys_to_bus(map);

 	/*
 	 * Ensure that the address returned is DMA'ble
 	 */
 	if (dma_capable(dev, dev_addr, size))
 		return dev_addr;

 	attrs |= DMA_ATTR_SKIP_CPU_SYNC;
 	swiotlb_tbl_unmap_single(dev, map, size, dir, attrs);

 	return DMA_ERROR_CODE;
 }
 EXPORT_SYMBOL_GPL(xen_swiotlb_map_page);

 /*
  * Unmap a single streaming mode DMA translation.  The dma_addr and size must
  * match what was provided for in a previous xen_swiotlb_map_page call.  All
  * other usages are undefined.
  *
  * After this call, reads by the cpu to the buffer are guaranteed to see
  * whatever the device wrote there.
  */
 static void xen_unmap_single(struct device *hwdev, dma_addr_t dev_addr,
 			     size_t size, enum dma_data_direction dir,
 			     unsigned long attrs)
 {
 	phys_addr_t paddr = xen_bus_to_phys(dev_addr);

 	BUG_ON(dir == DMA_NONE);

 	xen_dma_unmap_page(hwdev, dev_addr, size, dir, attrs);

 	/* NOTE: We use dev_addr here, not paddr! */
 	if (is_xen_swiotlb_buffer(dev_addr)) {
 		swiotlb_tbl_unmap_single(hwdev, paddr, size, dir, attrs);
 		return;
 	}

 	if (dir != DMA_FROM_DEVICE)
 		return;

 	/*
 	 * phys_to_virt doesn't work with hihgmem page but we could
 	 * call dma_mark_clean() with hihgmem page here. However, we
 	 * are fine since dma_mark_clean() is null on POWERPC. We can
 	 * make dma_mark_clean() take a physical address if necessary.
 	 */
 	dma_mark_clean(phys_to_virt(paddr), size);
 }

 void xen_swiotlb_unmap_page(struct device *hwdev, dma_addr_t dev_addr,
 			    size_t size, enum dma_data_direction dir,
 			    unsigned long attrs)
 {
 	xen_unmap_single(hwdev, dev_addr, size, dir, attrs);
 }
 EXPORT_SYMBOL_GPL(xen_swiotlb_unmap_page);

 /*
  * Make physical memory consistent for a single streaming mode DMA translation
  * after a transfer.
  *
  * If you perform a xen_swiotlb_map_page() but wish to interrogate the buffer
  * using the cpu, yet do not wish to teardown the dma mapping, you must
  * call this function before doing so.  At the next point you give the dma
  * address back to the card, you must first perform a
  * xen_swiotlb_dma_sync_for_device, and then the device again owns the buffer
  */
 static void
 xen_swiotlb_sync_single(struct device *hwdev, dma_addr_t dev_addr,
 			size_t size, enum dma_data_direction dir,
 			enum dma_sync_target target)
 {
 	phys_addr_t paddr = xen_bus_to_phys(dev_addr);

 	BUG_ON(dir == DMA_NONE);

 	if (target == SYNC_FOR_CPU)
 		xen_dma_sync_single_for_cpu(hwdev, dev_addr, size, dir);

 	/* NOTE: We use dev_addr here, not paddr! */
 	if (is_xen_swiotlb_buffer(dev_addr))
 		swiotlb_tbl_sync_single(hwdev, paddr, size, dir, target);

 	if (target == SYNC_FOR_DEVICE)
 		xen_dma_sync_single_for_device(hwdev, dev_addr, size, dir);

 	if (dir != DMA_FROM_DEVICE)
 		return;

 	dma_mark_clean(phys_to_virt(paddr), size);
 }

 void
 xen_swiotlb_sync_single_for_cpu(struct device *hwdev, dma_addr_t dev_addr,
 				size_t size, enum dma_data_direction dir)
 {
 	xen_swiotlb_sync_single(hwdev, dev_addr, size, dir, SYNC_FOR_CPU);
 }
 EXPORT_SYMBOL_GPL(xen_swiotlb_sync_single_for_cpu);

 void
 xen_swiotlb_sync_single_for_device(struct device *hwdev, dma_addr_t dev_addr,
 				   size_t size, enum dma_data_direction dir)
 {
 	xen_swiotlb_sync_single(hwdev, dev_addr, size, dir, SYNC_FOR_DEVICE);
 }
 EXPORT_SYMBOL_GPL(xen_swiotlb_sync_single_for_device);

 /*
  * Map a set of buffers described by scatterlist in streaming mode for DMA.
  * This is the scatter-gather version of the above xen_swiotlb_map_page
  * interface.  Here the scatter gather list elements are each tagged with the
  * appropriate dma address and length.  They are obtained via
  * sg_dma_{address,length}(SG).
  *
  * NOTE: An implementation may be able to use a smaller number of
  *       DMA address/length pairs than there are SG table elements.
  *       (for example via virtual mapping capabilities)
  *       The routine returns the number of addr/length pairs actually
  *       used, at most nents.
  *
  * Device ownership issues as mentioned above for xen_swiotlb_map_page are the
  * same here.
  */
 int
 xen_swiotlb_map_sg_attrs(struct device *hwdev, struct scatterlist *sgl,
 			 int nelems, enum dma_data_direction dir,
 			 unsigned long attrs)
 {
 	struct scatterlist *sg;
 	int i;

 	BUG_ON(dir == DMA_NONE);

 	for_each_sg(sgl, sg, nelems, i) {
 		phys_addr_t paddr = sg_phys(sg);
 		dma_addr_t dev_addr = xen_phys_to_bus(paddr);

 		if (swiotlb_force ||
 		    xen_arch_need_swiotlb(hwdev, paddr, dev_addr) ||
 		    !dma_capable(hwdev, dev_addr, sg->length) ||
 		    range_straddles_page_boundary(paddr, sg->length)) {
 			phys_addr_t map = swiotlb_tbl_map_single(hwdev,
 								 start_dma_addr,
 								 sg_phys(sg),
 								 sg->length,
 								 dir, attrs);
 			if (map == SWIOTLB_MAP_ERROR) {
 				dev_warn(hwdev, "swiotlb buffer is full\n");
 				/* Don't panic here, we expect map_sg users
 				   to do proper error handling. */
 				attrs |= DMA_ATTR_SKIP_CPU_SYNC;
 				xen_swiotlb_unmap_sg_attrs(hwdev, sgl, i, dir,
 							   attrs);
 				sg_dma_len(sgl) = 0;
 				return 0;
 			}
 			xen_dma_map_page(hwdev, pfn_to_page(map >> PAGE_SHIFT),
 						dev_addr,
 						map & ~PAGE_MASK,
 						sg->length,
 						dir,
 						attrs);
 			sg->dma_address = xen_phys_to_bus(map);
 		} else {
 			/* we are not interested in the dma_addr returned by
 			 * xen_dma_map_page, only in the potential cache flushes executed
 			 * by the function. */
 			xen_dma_map_page(hwdev, pfn_to_page(paddr >> PAGE_SHIFT),
 						dev_addr,
 						paddr & ~PAGE_MASK,
 						sg->length,
 						dir,
 						attrs);
 			sg->dma_address = dev_addr;
 		}
 		sg_dma_len(sg) = sg->length;
 	}
 	return nelems;
 }
 EXPORT_SYMBOL_GPL(xen_swiotlb_map_sg_attrs);

 /*
  * Unmap a set of streaming mode DMA translations.  Again, cpu read rules
  * concerning calls here are the same as for swiotlb_unmap_page() above.
  */
 void
 xen_swiotlb_unmap_sg_attrs(struct device *hwdev, struct scatterlist *sgl,
 			   int nelems, enum dma_data_direction dir,
 			   unsigned long attrs)
 {
 	struct scatterlist *sg;
 	int i;

 	BUG_ON(dir == DMA_NONE);

 	for_each_sg(sgl, sg, nelems, i)
 		xen_unmap_single(hwdev, sg->dma_address, sg_dma_len(sg), dir, attrs);

 }
 EXPORT_SYMBOL_GPL(xen_swiotlb_unmap_sg_attrs);

 /*
  * Make physical memory consistent for a set of streaming mode DMA translations
  * after a transfer.
  *
  * The same as swiotlb_sync_single_* but for a scatter-gather list, same rules
  * and usage.
  */
 static void
 xen_swiotlb_sync_sg(struct device *hwdev, struct scatterlist *sgl,
 		    int nelems, enum dma_data_direction dir,
 		    enum dma_sync_target target)
 {
 	struct scatterlist *sg;
 	int i;

 	for_each_sg(sgl, sg, nelems, i)
 		xen_swiotlb_sync_single(hwdev, sg->dma_address,
 					sg_dma_len(sg), dir, target);
 }

 void
 xen_swiotlb_sync_sg_for_cpu(struct device *hwdev, struct scatterlist *sg,
 			    int nelems, enum dma_data_direction dir)
 {
 	xen_swiotlb_sync_sg(hwdev, sg, nelems, dir, SYNC_FOR_CPU);
 }
 EXPORT_SYMBOL_GPL(xen_swiotlb_sync_sg_for_cpu);

 void
 xen_swiotlb_sync_sg_for_device(struct device *hwdev, struct scatterlist *sg,
 			       int nelems, enum dma_data_direction dir)
 {
 	xen_swiotlb_sync_sg(hwdev, sg, nelems, dir, SYNC_FOR_DEVICE);
 }
 EXPORT_SYMBOL_GPL(xen_swiotlb_sync_sg_for_device);

 /*
  * Return whether the given device DMA address mask can be supported
  * properly.  For example, if your device can only drive the low 24-bits
  * during bus mastering, then you would pass 0x00ffffff as the mask to
  * this function.
  */
 int
 xen_swiotlb_dma_supported(struct device *hwdev, u64 mask)
 {
 	return xen_virt_to_bus(xen_io_tlb_end - 1) <= mask;
 }
 EXPORT_SYMBOL_GPL(xen_swiotlb_dma_supported);

 int
 xen_swiotlb_set_dma_mask(struct device *dev, u64 dma_mask)
 {
 	if (!dev->dma_mask || !xen_swiotlb_dma_supported(dev, dma_mask))
 		return -EIO;

 	*dev->dma_mask = dma_mask;

 	return 0;
 }
 EXPORT_SYMBOL_GPL(xen_swiotlb_set_dma_mask);
	/*
	* Copyright 2010
	* by Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
	*
	* This code provides a IOMMU for Xen PV guests with PCI passthrough.
	*
	* This program is free software; you can redistribute it and/or modify
	* it under the terms of the GNU General Public License v2.0 as published by
	* the Free Software Foundation
	*
	* This program is distributed in the hope that it will be useful,
	* but WITHOUT ANY WARRANTY; without even the implied warranty of
	* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
	* GNU General Public License for more details.
	*
	* PV guests under Xen are running in an non-contiguous memory architecture.
	*
	* When PCI pass-through is utilized, this necessitates an IOMMU for
	* translating bus (DMA) to virtual and vice-versa and also providing a
	* mechanism to have contiguous pages for device drivers operations (say DMA
	* operations).
	*
	* Specifically, under Xen the Linux idea of pages is an illusion. It
	* assumes that pages start at zero and go up to the available memory. To
	* help with that, the Linux Xen MMU provides a lookup mechanism to
	* translate the page frame numbers (PFN) to machine frame numbers (MFN)
	* and vice-versa. The MFN are the "real" frame numbers. Furthermore
	* memory is not contiguous. Xen hypervisor stitches memory for guests
	* from different pools, which means there is no guarantee that PFN==MFN
	* and PFN+1==MFN+1. Lastly with Xen 4.0, pages (in debug mode) are
	* allocated in descending order (high to low), meaning the guest might
	* never get any MFN's under the 4GB mark.
	*
	*/

	#define pr_fmt(fmt) "xen:" KBUILD_MODNAME ": " fmt

	#include <linux/bootmem.h>
	#include <linux/dma-mapping.h>
	#include <linux/export.h>
	#include <xen/swiotlb-xen.h>
	#include <xen/page.h>
	#include <xen/xen-ops.h>
	#include <xen/hvc-console.h>

	#include <asm/dma-mapping.h>
	#include <asm/xen/page-coherent.h>

	#include <trace/events/swiotlb.h>
	/*
	* Used to do a quick range check in swiotlb_tbl_unmap_single and
	* swiotlb_tbl_sync_single_*, to see if the memory was in fact allocated by this
	* API.
	*/

	#ifndef CONFIG_X86
	static unsigned long dma_alloc_coherent_mask(struct device *dev,
	gfp_t gfp)
	{
	unsigned long dma_mask = 0;

	dma_mask = dev->coherent_dma_mask;
	if (!dma_mask)
	dma_mask = (gfp & GFP_DMA) ? DMA_BIT_MASK(24) : DMA_BIT_MASK(32);

	return dma_mask;
	}
	#endif

	static char xen_io_tlb_start, xen_io_tlb_end;
	static unsigned long xen_io_tlb_nslabs;
	/*
	* Quick lookup value of the bus address of the IOTLB.
	*/

	static u64 start_dma_addr;

	/*
	* Both of these functions should avoid XEN_PFN_PHYS because phys_addr_t
	* can be 32bit when dma_addr_t is 64bit leading to a loss in
	* information if the shift is done before casting to 64bit.
	*/
	static inline dma_addr_t xen_phys_to_bus(phys_addr_t paddr)
	{
	unsigned long bfn = pfn_to_bfn(XEN_PFN_DOWN(paddr));
	dma_addr_t dma = (dma_addr_t)bfn << XEN_PAGE_SHIFT;

	dma \|= paddr & ~XEN_PAGE_MASK;

	return dma;
	}

	static inline phys_addr_t xen_bus_to_phys(dma_addr_t baddr)
	{
	unsigned long xen_pfn = bfn_to_pfn(XEN_PFN_DOWN(baddr));
	dma_addr_t dma = (dma_addr_t)xen_pfn << XEN_PAGE_SHIFT;
	phys_addr_t paddr = dma;

	paddr \|= baddr & ~XEN_PAGE_MASK;

	return paddr;
	}

	static inline dma_addr_t xen_virt_to_bus(void *address)
	{
	return xen_phys_to_bus(virt_to_phys(address));
	}

	static int check_pages_physically_contiguous(unsigned long xen_pfn,
	unsigned int offset,
	size_t length)
	{
	unsigned long next_bfn;
	int i;
	int nr_pages;

	next_bfn = pfn_to_bfn(xen_pfn);
	nr_pages = (offset + length + XEN_PAGE_SIZE-1) >> XEN_PAGE_SHIFT;

	for (i = 1; i < nr_pages; i++) {
	if (pfn_to_bfn(++xen_pfn) != ++next_bfn)
	return 0;
	}
	return 1;
	}

	static inline int range_straddles_page_boundary(phys_addr_t p, size_t size)
	{
	unsigned long xen_pfn = XEN_PFN_DOWN(p);
	unsigned int offset = p & ~XEN_PAGE_MASK;

	if (offset + size <= XEN_PAGE_SIZE)
	return 0;
	if (check_pages_physically_contiguous(xen_pfn, offset, size))
	return 0;
	return 1;
	}

	static int is_xen_swiotlb_buffer(dma_addr_t dma_addr)
	{
	unsigned long bfn = XEN_PFN_DOWN(dma_addr);
	unsigned long xen_pfn = bfn_to_local_pfn(bfn);
	phys_addr_t paddr = XEN_PFN_PHYS(xen_pfn);

	/* If the address is outside our domain, it CAN
	* have the same virtual address as another address
	* in our domain. Therefore _only_ check address within our domain.
	*/
	if (pfn_valid(PFN_DOWN(paddr))) {
	return paddr >= virt_to_phys(xen_io_tlb_start) &&
	paddr < virt_to_phys(xen_io_tlb_end);
	}
	return 0;
	}

	static int max_dma_bits = 32;

	static int
	xen_swiotlb_fixup(void *buf, size_t size, unsigned long nslabs)
	{
	int i, rc;
	int dma_bits;
	dma_addr_t dma_handle;
	phys_addr_t p = virt_to_phys(buf);

	dma_bits = get_order(IO_TLB_SEGSIZE << IO_TLB_SHIFT) + PAGE_SHIFT;

	i = 0;
	do {
	int slabs = min(nslabs - i, (unsigned long)IO_TLB_SEGSIZE);

	do {
	rc = xen_create_contiguous_region(
	p + (i << IO_TLB_SHIFT),
	get_order(slabs << IO_TLB_SHIFT),
	dma_bits, &dma_handle);
	} while (rc && dma_bits++ < max_dma_bits);
	if (rc)
	return rc;

	i += slabs;
	} while (i < nslabs);
	return 0;
	}
	static unsigned long xen_set_nslabs(unsigned long nr_tbl)
	{
	if (!nr_tbl) {
	xen_io_tlb_nslabs = (64 * 1024 * 1024 >> IO_TLB_SHIFT);
	xen_io_tlb_nslabs = ALIGN(xen_io_tlb_nslabs, IO_TLB_SEGSIZE);
	} else
	xen_io_tlb_nslabs = nr_tbl;

	return xen_io_tlb_nslabs << IO_TLB_SHIFT;
	}

	enum xen_swiotlb_err {
	XEN_SWIOTLB_UNKNOWN = 0,
	XEN_SWIOTLB_ENOMEM,
	XEN_SWIOTLB_EFIXUP
	};

	static const char *xen_swiotlb_error(enum xen_swiotlb_err err)
	{
	switch (err) {
	case XEN_SWIOTLB_ENOMEM:
	return "Cannot allocate Xen-SWIOTLB buffer\n";
	case XEN_SWIOTLB_EFIXUP:
	return "Failed to get contiguous memory for DMA from Xen!\n"\
	"You either: don't have the permissions, do not have"\
	" enough free memory under 4GB, or the hypervisor memory"\
	" is too fragmented!";
	default:
	break;
	}
	return "";
	}
	int __ref xen_swiotlb_init(int verbose, bool early)
	{
	unsigned long bytes, order;
	int rc = -ENOMEM;
	enum xen_swiotlb_err m_ret = XEN_SWIOTLB_UNKNOWN;
	unsigned int repeat = 3;

	xen_io_tlb_nslabs = swiotlb_nr_tbl();
	retry:
	bytes = xen_set_nslabs(xen_io_tlb_nslabs);
	order = get_order(xen_io_tlb_nslabs << IO_TLB_SHIFT);
	/*
	* Get IO TLB memory from any location.
	*/
	if (early)
	xen_io_tlb_start = alloc_bootmem_pages(PAGE_ALIGN(bytes));
	else {
	#define SLABS_PER_PAGE (1 << (PAGE_SHIFT - IO_TLB_SHIFT))
	#define IO_TLB_MIN_SLABS ((1<<20) >> IO_TLB_SHIFT)
	while ((SLABS_PER_PAGE << order) > IO_TLB_MIN_SLABS) {
	xen_io_tlb_start = (void *)xen_get_swiotlb_free_pages(order);
	if (xen_io_tlb_start)
	break;
	order--;
	}
	if (order != get_order(bytes)) {
	pr_warn("Warning: only able to allocate %ld MB for software IO TLB\n",
	(PAGE_SIZE << order) >> 20);
	xen_io_tlb_nslabs = SLABS_PER_PAGE << order;
	bytes = xen_io_tlb_nslabs << IO_TLB_SHIFT;
	}
	}
	if (!xen_io_tlb_start) {
	m_ret = XEN_SWIOTLB_ENOMEM;
	goto error;
	}
	xen_io_tlb_end = xen_io_tlb_start + bytes;
	/*
	* And replace that memory with pages under 4GB.
	*/
	rc = xen_swiotlb_fixup(xen_io_tlb_start,
	bytes,
	xen_io_tlb_nslabs);
	if (rc) {
	if (early)
	free_bootmem(__pa(xen_io_tlb_start), PAGE_ALIGN(bytes));
	else {
	free_pages((unsigned long)xen_io_tlb_start, order);
	xen_io_tlb_start = NULL;
	}
	m_ret = XEN_SWIOTLB_EFIXUP;
	goto error;
	}
	start_dma_addr = xen_virt_to_bus(xen_io_tlb_start);
	if (early) {
	if (swiotlb_init_with_tbl(xen_io_tlb_start, xen_io_tlb_nslabs,
	verbose))
	panic("Cannot allocate SWIOTLB buffer");
	rc = 0;
	} else
	rc = swiotlb_late_init_with_tbl(xen_io_tlb_start, xen_io_tlb_nslabs);
	return rc;
	error:
	if (repeat--) {
	xen_io_tlb_nslabs = max(1024UL, /* Min is 2MB */
	(xen_io_tlb_nslabs >> 1));
	pr_info("Lowering to %luMB\n",
	(xen_io_tlb_nslabs << IO_TLB_SHIFT) >> 20);
	goto retry;
	}
	pr_err("%s (rc:%d)\n", xen_swiotlb_error(m_ret), rc);
	if (early)
	panic("%s (rc:%d)", xen_swiotlb_error(m_ret), rc);
	else
	free_pages((unsigned long)xen_io_tlb_start, order);
	return rc;
	}
	void *
	xen_swiotlb_alloc_coherent(struct device *hwdev, size_t size,
	dma_addr_t *dma_handle, gfp_t flags,
	unsigned long attrs)
	{
	void *ret;
	int order = get_order(size);
	u64 dma_mask = DMA_BIT_MASK(32);
	phys_addr_t phys;
	dma_addr_t dev_addr;

	/*
	* Ignore region specifiers - the kernel's ideas of
	* pseudo-phys memory layout has nothing to do with the
	* machine physical layout. We can't allocate highmem
	* because we can't return a pointer to it.
	*/
	flags &= ~(__GFP_DMA \| __GFP_HIGHMEM);

	/* On ARM this function returns an ioremap'ped virtual address for
	* which virt_to_phys doesn't return the corresponding physical
	* address. In fact on ARM virt_to_phys only works for kernel direct
	* mapped RAM memory. Also see comment below.
	*/
	ret = xen_alloc_coherent_pages(hwdev, size, dma_handle, flags, attrs);

	if (!ret)
	return ret;

	if (hwdev && hwdev->coherent_dma_mask)
	dma_mask = dma_alloc_coherent_mask(hwdev, flags);

	/* At this point dma_handle is the physical address, next we are
	* going to set it to the machine address.
	* Do not use virt_to_phys(ret) because on ARM it doesn't correspond
	* to dma_handle. /
	phys = *dma_handle;
	dev_addr = xen_phys_to_bus(phys);
	if (((dev_addr + size - 1 <= dma_mask)) &&
	!range_straddles_page_boundary(phys, size))
	*dma_handle = dev_addr;
	else {
	if (xen_create_contiguous_region(phys, order,
	fls64(dma_mask), dma_handle) != 0) {
	xen_free_coherent_pages(hwdev, size, ret, (dma_addr_t)phys, attrs);
	return NULL;
	}
	}
	memset(ret, 0, size);
	return ret;
	}
	EXPORT_SYMBOL_GPL(xen_swiotlb_alloc_coherent);

	void
	xen_swiotlb_free_coherent(struct device hwdev, size_t size, void vaddr,
	dma_addr_t dev_addr, unsigned long attrs)
	{
	int order = get_order(size);
	phys_addr_t phys;
	u64 dma_mask = DMA_BIT_MASK(32);

	if (hwdev && hwdev->coherent_dma_mask)
	dma_mask = hwdev->coherent_dma_mask;

	/* do not use virt_to_phys because on ARM it doesn't return you the
	* physical address */
	phys = xen_bus_to_phys(dev_addr);

	if (((dev_addr + size - 1 > dma_mask)) \|\|
	range_straddles_page_boundary(phys, size))
	xen_destroy_contiguous_region(phys, order);

	xen_free_coherent_pages(hwdev, size, vaddr, (dma_addr_t)phys, attrs);
	}
	EXPORT_SYMBOL_GPL(xen_swiotlb_free_coherent);


	/*
	* Map a single buffer of the indicated size for DMA in streaming mode. The
	* physical address to use is returned.
	*
	* Once the device is given the dma address, the device owns this memory until
	* either xen_swiotlb_unmap_page or xen_swiotlb_dma_sync_single is performed.
	*/
	dma_addr_t xen_swiotlb_map_page(struct device dev, struct page page,
	unsigned long offset, size_t size,
	enum dma_data_direction dir,
	unsigned long attrs)
	{
	phys_addr_t map, phys = page_to_phys(page) + offset;
	dma_addr_t dev_addr = xen_phys_to_bus(phys);

	BUG_ON(dir == DMA_NONE);
	/*
	* If the address happens to be in the device's DMA window,
	* we can safely return the device addr and not worry about bounce
	* buffering it.
	*/
	if (dma_capable(dev, dev_addr, size) &&
	!range_straddles_page_boundary(phys, size) &&
	!xen_arch_need_swiotlb(dev, phys, dev_addr) &&
	!swiotlb_force) {
	/* we are not interested in the dma_addr returned by
	* xen_dma_map_page, only in the potential cache flushes executed
	* by the function. */
	xen_dma_map_page(dev, page, dev_addr, offset, size, dir, attrs);
	return dev_addr;
	}

	/*
	* Oh well, have to allocate and map a bounce buffer.
	*/
	trace_swiotlb_bounced(dev, dev_addr, size, swiotlb_force);

	map = swiotlb_tbl_map_single(dev, start_dma_addr, phys, size, dir,
	attrs);
	if (map == SWIOTLB_MAP_ERROR)
	return DMA_ERROR_CODE;

	xen_dma_map_page(dev, pfn_to_page(map >> PAGE_SHIFT),
	dev_addr, map & ~PAGE_MASK, size, dir, attrs);
	dev_addr = xen_phys_to_bus(map);

	/*
	* Ensure that the address returned is DMA'ble
	*/
	if (dma_capable(dev, dev_addr, size))
	return dev_addr;

	attrs \|= DMA_ATTR_SKIP_CPU_SYNC;
	swiotlb_tbl_unmap_single(dev, map, size, dir, attrs);

	return DMA_ERROR_CODE;
	}
	EXPORT_SYMBOL_GPL(xen_swiotlb_map_page);

	/*
	* Unmap a single streaming mode DMA translation. The dma_addr and size must
	* match what was provided for in a previous xen_swiotlb_map_page call. All
	* other usages are undefined.
	*
	* After this call, reads by the cpu to the buffer are guaranteed to see
	* whatever the device wrote there.
	*/
	static void xen_unmap_single(struct device *hwdev, dma_addr_t dev_addr,
	size_t size, enum dma_data_direction dir,
	unsigned long attrs)
	{
	phys_addr_t paddr = xen_bus_to_phys(dev_addr);

	BUG_ON(dir == DMA_NONE);

	xen_dma_unmap_page(hwdev, dev_addr, size, dir, attrs);

	/* NOTE: We use dev_addr here, not paddr! */
	if (is_xen_swiotlb_buffer(dev_addr)) {
	swiotlb_tbl_unmap_single(hwdev, paddr, size, dir, attrs);
	return;
	}

	if (dir != DMA_FROM_DEVICE)
	return;

	/*
	* phys_to_virt doesn't work with hihgmem page but we could
	* call dma_mark_clean() with hihgmem page here. However, we
	* are fine since dma_mark_clean() is null on POWERPC. We can
	* make dma_mark_clean() take a physical address if necessary.
	*/
	dma_mark_clean(phys_to_virt(paddr), size);
	}

	void xen_swiotlb_unmap_page(struct device *hwdev, dma_addr_t dev_addr,
	size_t size, enum dma_data_direction dir,
	unsigned long attrs)
	{
	xen_unmap_single(hwdev, dev_addr, size, dir, attrs);
	}
	EXPORT_SYMBOL_GPL(xen_swiotlb_unmap_page);

	/*
	* Make physical memory consistent for a single streaming mode DMA translation
	* after a transfer.
	*
	* If you perform a xen_swiotlb_map_page() but wish to interrogate the buffer
	* using the cpu, yet do not wish to teardown the dma mapping, you must
	* call this function before doing so. At the next point you give the dma
	* address back to the card, you must first perform a
	* xen_swiotlb_dma_sync_for_device, and then the device again owns the buffer
	*/
	static void
	xen_swiotlb_sync_single(struct device *hwdev, dma_addr_t dev_addr,
	size_t size, enum dma_data_direction dir,
	enum dma_sync_target target)
	{
	phys_addr_t paddr = xen_bus_to_phys(dev_addr);

	BUG_ON(dir == DMA_NONE);

	if (target == SYNC_FOR_CPU)
	xen_dma_sync_single_for_cpu(hwdev, dev_addr, size, dir);

	/* NOTE: We use dev_addr here, not paddr! */
	if (is_xen_swiotlb_buffer(dev_addr))
	swiotlb_tbl_sync_single(hwdev, paddr, size, dir, target);

	if (target == SYNC_FOR_DEVICE)
	xen_dma_sync_single_for_device(hwdev, dev_addr, size, dir);

	if (dir != DMA_FROM_DEVICE)
	return;

	dma_mark_clean(phys_to_virt(paddr), size);
	}

	void
	xen_swiotlb_sync_single_for_cpu(struct device *hwdev, dma_addr_t dev_addr,
	size_t size, enum dma_data_direction dir)
	{
	xen_swiotlb_sync_single(hwdev, dev_addr, size, dir, SYNC_FOR_CPU);
	}
	EXPORT_SYMBOL_GPL(xen_swiotlb_sync_single_for_cpu);

	void
	xen_swiotlb_sync_single_for_device(struct device *hwdev, dma_addr_t dev_addr,
	size_t size, enum dma_data_direction dir)
	{
	xen_swiotlb_sync_single(hwdev, dev_addr, size, dir, SYNC_FOR_DEVICE);
	}
	EXPORT_SYMBOL_GPL(xen_swiotlb_sync_single_for_device);

	/*
	* Map a set of buffers described by scatterlist in streaming mode for DMA.
	* This is the scatter-gather version of the above xen_swiotlb_map_page
	* interface. Here the scatter gather list elements are each tagged with the
	* appropriate dma address and length. They are obtained via
	* sg_dma_{address,length}(SG).
	*
	* NOTE: An implementation may be able to use a smaller number of
	* DMA address/length pairs than there are SG table elements.
	* (for example via virtual mapping capabilities)
	* The routine returns the number of addr/length pairs actually
	* used, at most nents.
	*
	* Device ownership issues as mentioned above for xen_swiotlb_map_page are the
	* same here.
	*/
	int
	xen_swiotlb_map_sg_attrs(struct device hwdev, struct scatterlist sgl,
	int nelems, enum dma_data_direction dir,
	unsigned long attrs)
	{
	struct scatterlist *sg;
	int i;

	BUG_ON(dir == DMA_NONE);

	for_each_sg(sgl, sg, nelems, i) {
	phys_addr_t paddr = sg_phys(sg);
	dma_addr_t dev_addr = xen_phys_to_bus(paddr);

	if (swiotlb_force \|\|
	xen_arch_need_swiotlb(hwdev, paddr, dev_addr) \|\|
	!dma_capable(hwdev, dev_addr, sg->length) \|\|
	range_straddles_page_boundary(paddr, sg->length)) {
	phys_addr_t map = swiotlb_tbl_map_single(hwdev,
	start_dma_addr,
	sg_phys(sg),
	sg->length,
	dir, attrs);
	if (map == SWIOTLB_MAP_ERROR) {
	dev_warn(hwdev, "swiotlb buffer is full\n");
	/* Don't panic here, we expect map_sg users
	to do proper error handling. */
	attrs \|= DMA_ATTR_SKIP_CPU_SYNC;
	xen_swiotlb_unmap_sg_attrs(hwdev, sgl, i, dir,
	attrs);
	sg_dma_len(sgl) = 0;
	return 0;
	}
	xen_dma_map_page(hwdev, pfn_to_page(map >> PAGE_SHIFT),
	dev_addr,
	map & ~PAGE_MASK,
	sg->length,
	dir,
	attrs);
	sg->dma_address = xen_phys_to_bus(map);
	} else {
	/* we are not interested in the dma_addr returned by
	* xen_dma_map_page, only in the potential cache flushes executed
	* by the function. */
	xen_dma_map_page(hwdev, pfn_to_page(paddr >> PAGE_SHIFT),
	dev_addr,
	paddr & ~PAGE_MASK,
	sg->length,
	dir,
	attrs);
	sg->dma_address = dev_addr;
	}
	sg_dma_len(sg) = sg->length;
	}
	return nelems;
	}
	EXPORT_SYMBOL_GPL(xen_swiotlb_map_sg_attrs);

	/*
	* Unmap a set of streaming mode DMA translations. Again, cpu read rules
	* concerning calls here are the same as for swiotlb_unmap_page() above.
	*/
	void
	xen_swiotlb_unmap_sg_attrs(struct device hwdev, struct scatterlist sgl,
	int nelems, enum dma_data_direction dir,
	unsigned long attrs)
	{
	struct scatterlist *sg;
	int i;

	BUG_ON(dir == DMA_NONE);

	for_each_sg(sgl, sg, nelems, i)
	xen_unmap_single(hwdev, sg->dma_address, sg_dma_len(sg), dir, attrs);

	}
	EXPORT_SYMBOL_GPL(xen_swiotlb_unmap_sg_attrs);

	/*
	* Make physical memory consistent for a set of streaming mode DMA translations
	* after a transfer.
	*
	* The same as swiotlb_sync_single_* but for a scatter-gather list, same rules
	* and usage.
	*/
	static void
	xen_swiotlb_sync_sg(struct device hwdev, struct scatterlist sgl,
	int nelems, enum dma_data_direction dir,
	enum dma_sync_target target)
	{
	struct scatterlist *sg;
	int i;

	for_each_sg(sgl, sg, nelems, i)
	xen_swiotlb_sync_single(hwdev, sg->dma_address,
	sg_dma_len(sg), dir, target);
	}

	void
	xen_swiotlb_sync_sg_for_cpu(struct device hwdev, struct scatterlist sg,
	int nelems, enum dma_data_direction dir)
	{
	xen_swiotlb_sync_sg(hwdev, sg, nelems, dir, SYNC_FOR_CPU);
	}
	EXPORT_SYMBOL_GPL(xen_swiotlb_sync_sg_for_cpu);

	void
	xen_swiotlb_sync_sg_for_device(struct device hwdev, struct scatterlist sg,
	int nelems, enum dma_data_direction dir)
	{
	xen_swiotlb_sync_sg(hwdev, sg, nelems, dir, SYNC_FOR_DEVICE);
	}
	EXPORT_SYMBOL_GPL(xen_swiotlb_sync_sg_for_device);

	/*
	* Return whether the given device DMA address mask can be supported
	* properly. For example, if your device can only drive the low 24-bits
	* during bus mastering, then you would pass 0x00ffffff as the mask to
	* this function.
	*/
	int
	xen_swiotlb_dma_supported(struct device *hwdev, u64 mask)
	{
	return xen_virt_to_bus(xen_io_tlb_end - 1) <= mask;
	}
	EXPORT_SYMBOL_GPL(xen_swiotlb_dma_supported);

	int
	xen_swiotlb_set_dma_mask(struct device *dev, u64 dma_mask)
	{
	if (!dev->dma_mask \|\| !xen_swiotlb_dma_supported(dev, dma_mask))
	return -EIO;

	*dev->dma_mask = dma_mask;

	return 0;
	}
	EXPORT_SYMBOL_GPL(xen_swiotlb_set_dma_mask);