drivers/xen/swiotlb-xen.c - kernel/mindspeed - Git at Google

 /*
  *  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.
  *
  */

 #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>
 /*
  * 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.
  */

 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.
  */

 u64 start_dma_addr;

 static dma_addr_t xen_phys_to_bus(phys_addr_t paddr)
 {
 	return phys_to_machine(XPADDR(paddr)).maddr;
 }

 static phys_addr_t xen_bus_to_phys(dma_addr_t baddr)
 {
 	return machine_to_phys(XMADDR(baddr)).paddr;
 }

 static 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 pfn,
 					     unsigned int offset,
 					     size_t length)
 {
 	unsigned long next_mfn;
 	int i;
 	int nr_pages;

 	next_mfn = pfn_to_mfn(pfn);
 	nr_pages = (offset + length + PAGE_SIZE-1) >> PAGE_SHIFT;

 	for (i = 1; i < nr_pages; i++) {
 		if (pfn_to_mfn(++pfn) != ++next_mfn)
 			return 0;
 	}
 	return 1;
 }

 static int range_straddles_page_boundary(phys_addr_t p, size_t size)
 {
 	unsigned long pfn = PFN_DOWN(p);
 	unsigned int offset = p & ~PAGE_MASK;

 	if (offset + size <= PAGE_SIZE)
 		return 0;
 	if (check_pages_physically_contiguous(pfn, offset, size))
 		return 0;
 	return 1;
 }

 static int is_xen_swiotlb_buffer(dma_addr_t dma_addr)
 {
 	unsigned long mfn = PFN_DOWN(dma_addr);
 	unsigned long pfn = mfn_to_local_pfn(mfn);
 	phys_addr_t paddr;

 	/* 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)) {
 		paddr = PFN_PHYS(pfn);
 		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_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(
 				(unsigned long)buf + (i << IO_TLB_SHIFT),
 				get_order(slabs << IO_TLB_SHIFT),
 				dma_bits);
 		} while (rc && dma_bits++ < max_dma_bits);
 		if (rc)
 			return rc;

 		i += slabs;
 	} while (i < nslabs);
 	return 0;
 }

 void __init xen_swiotlb_init(int verbose)
 {
 	unsigned long bytes;
 	int rc = -ENOMEM;
 	unsigned long nr_tbl;
 	char *m = NULL;
 	unsigned int repeat = 3;

 	nr_tbl = swioltb_nr_tbl();
 	if (nr_tbl)
 		xen_io_tlb_nslabs = nr_tbl;
 	else {
 		xen_io_tlb_nslabs = (64 * 1024 * 1024 >> IO_TLB_SHIFT);
 		xen_io_tlb_nslabs = ALIGN(xen_io_tlb_nslabs, IO_TLB_SEGSIZE);
 	}
 retry:
 	bytes = xen_io_tlb_nslabs << IO_TLB_SHIFT;

 	/*
 	 * Get IO TLB memory from any location.
 	 */
 	xen_io_tlb_start = alloc_bootmem_pages(PAGE_ALIGN(bytes));
 	if (!xen_io_tlb_start) {
 		m = "Cannot allocate Xen-SWIOTLB buffer!\n";
 		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) {
 		free_bootmem(__pa(xen_io_tlb_start), PAGE_ALIGN(bytes));
 		m = "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!";
 		goto error;
 	}
 	start_dma_addr = xen_virt_to_bus(xen_io_tlb_start);
 	swiotlb_init_with_tbl(xen_io_tlb_start, xen_io_tlb_nslabs, verbose);

 	return;
 error:
 	if (repeat--) {
 		xen_io_tlb_nslabs = max(1024UL, /* Min is 2MB */
 					(xen_io_tlb_nslabs >> 1));
 		printk(KERN_INFO "Xen-SWIOTLB: Lowering to %luMB\n",
 		      (xen_io_tlb_nslabs << IO_TLB_SHIFT) >> 20);
 		goto retry;
 	}
 	xen_raw_printk("%s (rc:%d)", m, rc);
 	panic("%s (rc:%d)", m, rc);
 }

 void *
 xen_swiotlb_alloc_coherent(struct device *hwdev, size_t size,
 			   dma_addr_t *dma_handle, gfp_t flags)
 {
 	void *ret;
 	int order = get_order(size);
 	u64 dma_mask = DMA_BIT_MASK(32);
 	unsigned long vstart;
 	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);

 	if (dma_alloc_from_coherent(hwdev, size, dma_handle, &ret))
 		return ret;

 	vstart = __get_free_pages(flags, order);
 	ret = (void *)vstart;

 	if (!ret)
 		return ret;

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

 	phys = virt_to_phys(ret);
 	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(vstart, order,
 						 fls64(dma_mask)) != 0) {
 			free_pages(vstart, order);
 			return NULL;
 		}
 		*dma_handle = virt_to_machine(ret).maddr;
 	}
 	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)
 {
 	int order = get_order(size);
 	phys_addr_t phys;
 	u64 dma_mask = DMA_BIT_MASK(32);

 	if (dma_release_from_coherent(hwdev, order, vaddr))
 		return;

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

 	phys = virt_to_phys(vaddr);

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

 	free_pages((unsigned long)vaddr, order);
 }
 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,
 				struct dma_attrs *attrs)
 {
 	phys_addr_t phys = page_to_phys(page) + offset;
 	dma_addr_t dev_addr = xen_phys_to_bus(phys);
 	void *map;

 	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) && !swiotlb_force)
 		return dev_addr;

 	/*
 	 * Oh well, have to allocate and map a bounce buffer.
 	 */
 	map = swiotlb_tbl_map_single(dev, start_dma_addr, phys, size, dir);
 	if (!map)
 		return DMA_ERROR_CODE;

 	dev_addr = xen_virt_to_bus(map);

 	/*
 	 * Ensure that the address returned is DMA'ble
 	 */
 	if (!dma_capable(dev, dev_addr, size)) {
 		swiotlb_tbl_unmap_single(dev, map, size, dir);
 		dev_addr = 0;
 	}
 	return dev_addr;
 }
 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)
 {
 	phys_addr_t paddr = xen_bus_to_phys(dev_addr);

 	BUG_ON(dir == DMA_NONE);

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

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

 	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,
 			 struct dma_attrs *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 ||
 		    !dma_capable(hwdev, dev_addr, sg->length) ||
 		    range_straddles_page_boundary(paddr, sg->length)) {
 			void *map = swiotlb_tbl_map_single(hwdev,
 							   start_dma_addr,
 							   sg_phys(sg),
 							   sg->length, dir);
 			if (!map) {
 				/* Don't panic here, we expect map_sg users
 				   to do proper error handling. */
 				xen_swiotlb_unmap_sg_attrs(hwdev, sgl, i, dir,
 							   attrs);
 				sgl[0].dma_length = 0;
 				return DMA_ERROR_CODE;
 			}
 			sg->dma_address = xen_virt_to_bus(map);
 		} else
 			sg->dma_address = dev_addr;
 		sg->dma_length = sg->length;
 	}
 	return nelems;
 }
 EXPORT_SYMBOL_GPL(xen_swiotlb_map_sg_attrs);

 int
 xen_swiotlb_map_sg(struct device *hwdev, struct scatterlist *sgl, int nelems,
 		   enum dma_data_direction dir)
 {
 	return xen_swiotlb_map_sg_attrs(hwdev, sgl, nelems, dir, NULL);
 }
 EXPORT_SYMBOL_GPL(xen_swiotlb_map_sg);

 /*
  * 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,
 			   struct dma_attrs *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_length, dir);

 }
 EXPORT_SYMBOL_GPL(xen_swiotlb_unmap_sg_attrs);

 void
 xen_swiotlb_unmap_sg(struct device *hwdev, struct scatterlist *sgl, int nelems,
 		     enum dma_data_direction dir)
 {
 	return xen_swiotlb_unmap_sg_attrs(hwdev, sgl, nelems, dir, NULL);
 }
 EXPORT_SYMBOL_GPL(xen_swiotlb_unmap_sg);

 /*
  * 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_length, 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);

 int
 xen_swiotlb_dma_mapping_error(struct device *hwdev, dma_addr_t dma_addr)
 {
 	return !dma_addr;
 }
 EXPORT_SYMBOL_GPL(xen_swiotlb_dma_mapping_error);

 /*
  * 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);
	/*
	* 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.
	*
	*/

	#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>
	/*
	* 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.
	*/

	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.
	*/

	u64 start_dma_addr;

	static dma_addr_t xen_phys_to_bus(phys_addr_t paddr)
	{
	return phys_to_machine(XPADDR(paddr)).maddr;
	}

	static phys_addr_t xen_bus_to_phys(dma_addr_t baddr)
	{
	return machine_to_phys(XMADDR(baddr)).paddr;
	}

	static 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 pfn,
	unsigned int offset,
	size_t length)
	{
	unsigned long next_mfn;
	int i;
	int nr_pages;

	next_mfn = pfn_to_mfn(pfn);
	nr_pages = (offset + length + PAGE_SIZE-1) >> PAGE_SHIFT;

	for (i = 1; i < nr_pages; i++) {
	if (pfn_to_mfn(++pfn) != ++next_mfn)
	return 0;
	}
	return 1;
	}

	static int range_straddles_page_boundary(phys_addr_t p, size_t size)
	{
	unsigned long pfn = PFN_DOWN(p);
	unsigned int offset = p & ~PAGE_MASK;

	if (offset + size <= PAGE_SIZE)
	return 0;
	if (check_pages_physically_contiguous(pfn, offset, size))
	return 0;
	return 1;
	}

	static int is_xen_swiotlb_buffer(dma_addr_t dma_addr)
	{
	unsigned long mfn = PFN_DOWN(dma_addr);
	unsigned long pfn = mfn_to_local_pfn(mfn);
	phys_addr_t paddr;

	/* 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)) {
	paddr = PFN_PHYS(pfn);
	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_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(
	(unsigned long)buf + (i << IO_TLB_SHIFT),
	get_order(slabs << IO_TLB_SHIFT),
	dma_bits);
	} while (rc && dma_bits++ < max_dma_bits);
	if (rc)
	return rc;

	i += slabs;
	} while (i < nslabs);
	return 0;
	}

	void __init xen_swiotlb_init(int verbose)
	{
	unsigned long bytes;
	int rc = -ENOMEM;
	unsigned long nr_tbl;
	char *m = NULL;
	unsigned int repeat = 3;

	nr_tbl = swioltb_nr_tbl();
	if (nr_tbl)
	xen_io_tlb_nslabs = nr_tbl;
	else {
	xen_io_tlb_nslabs = (64 * 1024 * 1024 >> IO_TLB_SHIFT);
	xen_io_tlb_nslabs = ALIGN(xen_io_tlb_nslabs, IO_TLB_SEGSIZE);
	}
	retry:
	bytes = xen_io_tlb_nslabs << IO_TLB_SHIFT;

	/*
	* Get IO TLB memory from any location.
	*/
	xen_io_tlb_start = alloc_bootmem_pages(PAGE_ALIGN(bytes));
	if (!xen_io_tlb_start) {
	m = "Cannot allocate Xen-SWIOTLB buffer!\n";
	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) {
	free_bootmem(__pa(xen_io_tlb_start), PAGE_ALIGN(bytes));
	m = "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!";
	goto error;
	}
	start_dma_addr = xen_virt_to_bus(xen_io_tlb_start);
	swiotlb_init_with_tbl(xen_io_tlb_start, xen_io_tlb_nslabs, verbose);

	return;
	error:
	if (repeat--) {
	xen_io_tlb_nslabs = max(1024UL, /* Min is 2MB */
	(xen_io_tlb_nslabs >> 1));
	printk(KERN_INFO "Xen-SWIOTLB: Lowering to %luMB\n",
	(xen_io_tlb_nslabs << IO_TLB_SHIFT) >> 20);
	goto retry;
	}
	xen_raw_printk("%s (rc:%d)", m, rc);
	panic("%s (rc:%d)", m, rc);
	}

	void *
	xen_swiotlb_alloc_coherent(struct device *hwdev, size_t size,
	dma_addr_t *dma_handle, gfp_t flags)
	{
	void *ret;
	int order = get_order(size);
	u64 dma_mask = DMA_BIT_MASK(32);
	unsigned long vstart;
	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);

	if (dma_alloc_from_coherent(hwdev, size, dma_handle, &ret))
	return ret;

	vstart = __get_free_pages(flags, order);
	ret = (void *)vstart;

	if (!ret)
	return ret;

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

	phys = virt_to_phys(ret);
	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(vstart, order,
	fls64(dma_mask)) != 0) {
	free_pages(vstart, order);
	return NULL;
	}
	*dma_handle = virt_to_machine(ret).maddr;
	}
	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)
	{
	int order = get_order(size);
	phys_addr_t phys;
	u64 dma_mask = DMA_BIT_MASK(32);

	if (dma_release_from_coherent(hwdev, order, vaddr))
	return;

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

	phys = virt_to_phys(vaddr);

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

	free_pages((unsigned long)vaddr, order);
	}
	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,
	struct dma_attrs *attrs)
	{
	phys_addr_t phys = page_to_phys(page) + offset;
	dma_addr_t dev_addr = xen_phys_to_bus(phys);
	void *map;

	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) && !swiotlb_force)
	return dev_addr;

	/*
	* Oh well, have to allocate and map a bounce buffer.
	*/
	map = swiotlb_tbl_map_single(dev, start_dma_addr, phys, size, dir);
	if (!map)
	return DMA_ERROR_CODE;

	dev_addr = xen_virt_to_bus(map);

	/*
	* Ensure that the address returned is DMA'ble
	*/
	if (!dma_capable(dev, dev_addr, size)) {
	swiotlb_tbl_unmap_single(dev, map, size, dir);
	dev_addr = 0;
	}
	return dev_addr;
	}
	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)
	{
	phys_addr_t paddr = xen_bus_to_phys(dev_addr);

	BUG_ON(dir == DMA_NONE);

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

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

	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,
	struct dma_attrs *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 \|\|
	!dma_capable(hwdev, dev_addr, sg->length) \|\|
	range_straddles_page_boundary(paddr, sg->length)) {
	void *map = swiotlb_tbl_map_single(hwdev,
	start_dma_addr,
	sg_phys(sg),
	sg->length, dir);
	if (!map) {
	/* Don't panic here, we expect map_sg users
	to do proper error handling. */
	xen_swiotlb_unmap_sg_attrs(hwdev, sgl, i, dir,
	attrs);
	sgl[0].dma_length = 0;
	return DMA_ERROR_CODE;
	}
	sg->dma_address = xen_virt_to_bus(map);
	} else
	sg->dma_address = dev_addr;
	sg->dma_length = sg->length;
	}
	return nelems;
	}
	EXPORT_SYMBOL_GPL(xen_swiotlb_map_sg_attrs);

	int
	xen_swiotlb_map_sg(struct device hwdev, struct scatterlist sgl, int nelems,
	enum dma_data_direction dir)
	{
	return xen_swiotlb_map_sg_attrs(hwdev, sgl, nelems, dir, NULL);
	}
	EXPORT_SYMBOL_GPL(xen_swiotlb_map_sg);

	/*
	* 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,
	struct dma_attrs *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_length, dir);

	}
	EXPORT_SYMBOL_GPL(xen_swiotlb_unmap_sg_attrs);

	void
	xen_swiotlb_unmap_sg(struct device hwdev, struct scatterlist sgl, int nelems,
	enum dma_data_direction dir)
	{
	return xen_swiotlb_unmap_sg_attrs(hwdev, sgl, nelems, dir, NULL);
	}
	EXPORT_SYMBOL_GPL(xen_swiotlb_unmap_sg);

	/*
	* 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_length, 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);

	int
	xen_swiotlb_dma_mapping_error(struct device *hwdev, dma_addr_t dma_addr)
	{
	return !dma_addr;
	}
	EXPORT_SYMBOL_GPL(xen_swiotlb_dma_mapping_error);

	/*
	* 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);