alistair23-linux/drivers/iommu/dma-iommu.c

/*
 * A fairly generic DMA-API to IOMMU-API glue layer.
 *
 * Copyright (C) 2014-2015 ARM Ltd.
 *
 * based in part on arch/arm/mm/dma-mapping.c:
 * Copyright (C) 2000-2004 Russell King
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 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.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

#include <linux/acpi_iort.h>
#include <linux/device.h>
#include <linux/dma-iommu.h>
#include <linux/gfp.h>
#include <linux/huge_mm.h>
#include <linux/iommu.h>
#include <linux/iova.h>
#include <linux/irq.h>
#include <linux/mm.h>
#include <linux/pci.h>
#include <linux/scatterlist.h>
#include <linux/vmalloc.h>

struct iommu_dma_msi_page {
	struct list_head	list;
	dma_addr_t		iova;
	phys_addr_t		phys;
};

enum iommu_dma_cookie_type {
	IOMMU_DMA_IOVA_COOKIE,
	IOMMU_DMA_MSI_COOKIE,
};

struct iommu_dma_cookie {
	enum iommu_dma_cookie_type	type;
	union {
		/* Full allocator for IOMMU_DMA_IOVA_COOKIE */
		struct iova_domain	iovad;
		/* Trivial linear page allocator for IOMMU_DMA_MSI_COOKIE */
		dma_addr_t		msi_iova;
	};
	struct list_head		msi_page_list;
	spinlock_t			msi_lock;

	/* Domain for flush queue callback; NULL if flush queue not in use */
	struct iommu_domain		*fq_domain;
};

static inline size_t cookie_msi_granule(struct iommu_dma_cookie *cookie)
{
	if (cookie->type == IOMMU_DMA_IOVA_COOKIE)
		return cookie->iovad.granule;
	return PAGE_SIZE;
}

static struct iommu_dma_cookie *cookie_alloc(enum iommu_dma_cookie_type type)
{
	struct iommu_dma_cookie *cookie;

	cookie = kzalloc(sizeof(*cookie), GFP_KERNEL);
	if (cookie) {
		spin_lock_init(&cookie->msi_lock);
		INIT_LIST_HEAD(&cookie->msi_page_list);
		cookie->type = type;
	}
	return cookie;
}

int iommu_dma_init(void)
{
	return iova_cache_get();
}

/**
 * iommu_get_dma_cookie - Acquire DMA-API resources for a domain
 * @domain: IOMMU domain to prepare for DMA-API usage
 *
 * IOMMU drivers should normally call this from their domain_alloc
 * callback when domain->type == IOMMU_DOMAIN_DMA.
 */
int iommu_get_dma_cookie(struct iommu_domain *domain)
{
	if (domain->iova_cookie)
		return -EEXIST;

	domain->iova_cookie = cookie_alloc(IOMMU_DMA_IOVA_COOKIE);
	if (!domain->iova_cookie)
		return -ENOMEM;

	return 0;
}
EXPORT_SYMBOL(iommu_get_dma_cookie);

/**
 * iommu_get_msi_cookie - Acquire just MSI remapping resources
 * @domain: IOMMU domain to prepare
 * @base: Start address of IOVA region for MSI mappings
 *
 * Users who manage their own IOVA allocation and do not want DMA API support,
 * but would still like to take advantage of automatic MSI remapping, can use
 * this to initialise their own domain appropriately. Users should reserve a
 * contiguous IOVA region, starting at @base, large enough to accommodate the
 * number of PAGE_SIZE mappings necessary to cover every MSI doorbell address
 * used by the devices attached to @domain.
 */
int iommu_get_msi_cookie(struct iommu_domain *domain, dma_addr_t base)
{
	struct iommu_dma_cookie *cookie;

	if (domain->type != IOMMU_DOMAIN_UNMANAGED)
		return -EINVAL;

	if (domain->iova_cookie)
		return -EEXIST;

	cookie = cookie_alloc(IOMMU_DMA_MSI_COOKIE);
	if (!cookie)
		return -ENOMEM;

	cookie->msi_iova = base;
	domain->iova_cookie = cookie;
	return 0;
}
EXPORT_SYMBOL(iommu_get_msi_cookie);

/**
 * iommu_put_dma_cookie - Release a domain's DMA mapping resources
 * @domain: IOMMU domain previously prepared by iommu_get_dma_cookie() or
 *          iommu_get_msi_cookie()
 *
 * IOMMU drivers should normally call this from their domain_free callback.
 */
void iommu_put_dma_cookie(struct iommu_domain *domain)
{
	struct iommu_dma_cookie *cookie = domain->iova_cookie;
	struct iommu_dma_msi_page *msi, *tmp;

	if (!cookie)
		return;

	if (cookie->type == IOMMU_DMA_IOVA_COOKIE && cookie->iovad.granule)
		put_iova_domain(&cookie->iovad);

	list_for_each_entry_safe(msi, tmp, &cookie->msi_page_list, list) {
		list_del(&msi->list);
		kfree(msi);
	}
	kfree(cookie);
	domain->iova_cookie = NULL;
}
EXPORT_SYMBOL(iommu_put_dma_cookie);

/**
 * iommu_dma_get_resv_regions - Reserved region driver helper
 * @dev: Device from iommu_get_resv_regions()
 * @list: Reserved region list from iommu_get_resv_regions()
 *
 * IOMMU drivers can use this to implement their .get_resv_regions callback
 * for general non-IOMMU-specific reservations. Currently, this covers GICv3
 * ITS region reservation on ACPI based ARM platforms that may require HW MSI
 * reservation.
 */
void iommu_dma_get_resv_regions(struct device *dev, struct list_head *list)
{

	if (!is_of_node(dev_iommu_fwspec_get(dev)->iommu_fwnode))
		iort_iommu_msi_get_resv_regions(dev, list);

}
EXPORT_SYMBOL(iommu_dma_get_resv_regions);

static int cookie_init_hw_msi_region(struct iommu_dma_cookie *cookie,
		phys_addr_t start, phys_addr_t end)
{
	struct iova_domain *iovad = &cookie->iovad;
	struct iommu_dma_msi_page *msi_page;
	int i, num_pages;

	start -= iova_offset(iovad, start);
	num_pages = iova_align(iovad, end - start) >> iova_shift(iovad);

	msi_page = kcalloc(num_pages, sizeof(*msi_page), GFP_KERNEL);
	if (!msi_page)
		return -ENOMEM;

	for (i = 0; i < num_pages; i++) {
		msi_page[i].phys = start;
		msi_page[i].iova = start;
		INIT_LIST_HEAD(&msi_page[i].list);
		list_add(&msi_page[i].list, &cookie->msi_page_list);
		start += iovad->granule;
	}

	return 0;
}

static int iova_reserve_pci_windows(struct pci_dev *dev,
		struct iova_domain *iovad)
{
	struct pci_host_bridge *bridge = pci_find_host_bridge(dev->bus);
	struct resource_entry *window;
	unsigned long lo, hi;
	phys_addr_t start = 0, end;

	resource_list_for_each_entry(window, &bridge->windows) {
		if (resource_type(window->res) != IORESOURCE_MEM)
			continue;

		lo = iova_pfn(iovad, window->res->start - window->offset);
		hi = iova_pfn(iovad, window->res->end - window->offset);
		reserve_iova(iovad, lo, hi);
	}

	/* Get reserved DMA windows from host bridge */
	resource_list_for_each_entry(window, &bridge->dma_ranges) {
		end = window->res->start - window->offset;
resv_iova:
		if (end > start) {
			lo = iova_pfn(iovad, start);
			hi = iova_pfn(iovad, end);
			reserve_iova(iovad, lo, hi);
		} else {
			/* dma_ranges list should be sorted */
			dev_err(&dev->dev, "Failed to reserve IOVA\n");
			return -EINVAL;
		}

		start = window->res->end - window->offset + 1;
		/* If window is last entry */
		if (window->node.next == &bridge->dma_ranges &&
		    end != ~(dma_addr_t)0) {
			end = ~(dma_addr_t)0;
			goto resv_iova;
		}
	}

	return 0;
}

static int iova_reserve_iommu_regions(struct device *dev,
		struct iommu_domain *domain)
{
	struct iommu_dma_cookie *cookie = domain->iova_cookie;
	struct iova_domain *iovad = &cookie->iovad;
	struct iommu_resv_region *region;
	LIST_HEAD(resv_regions);
	int ret = 0;

	if (dev_is_pci(dev)) {
		ret = iova_reserve_pci_windows(to_pci_dev(dev), iovad);
		if (ret)
			return ret;
	}

	iommu_get_resv_regions(dev, &resv_regions);
	list_for_each_entry(region, &resv_regions, list) {
		unsigned long lo, hi;

		/* We ARE the software that manages these! */
		if (region->type == IOMMU_RESV_SW_MSI)
			continue;

		lo = iova_pfn(iovad, region->start);
		hi = iova_pfn(iovad, region->start + region->length - 1);
		reserve_iova(iovad, lo, hi);

		if (region->type == IOMMU_RESV_MSI)
			ret = cookie_init_hw_msi_region(cookie, region->start,
					region->start + region->length);
		if (ret)
			break;
	}
	iommu_put_resv_regions(dev, &resv_regions);

	return ret;
}

static void iommu_dma_flush_iotlb_all(struct iova_domain *iovad)
{
	struct iommu_dma_cookie *cookie;
	struct iommu_domain *domain;

	cookie = container_of(iovad, struct iommu_dma_cookie, iovad);
	domain = cookie->fq_domain;
	/*
	 * The IOMMU driver supporting DOMAIN_ATTR_DMA_USE_FLUSH_QUEUE
	 * implies that ops->flush_iotlb_all must be non-NULL.
	 */
	domain->ops->flush_iotlb_all(domain);
}

/**
 * iommu_dma_init_domain - Initialise a DMA mapping domain
 * @domain: IOMMU domain previously prepared by iommu_get_dma_cookie()
 * @base: IOVA at which the mappable address space starts
 * @size: Size of IOVA space
 * @dev: Device the domain is being initialised for
 *
 * @base and @size should be exact multiples of IOMMU page granularity to
 * avoid rounding surprises. If necessary, we reserve the page at address 0
 * to ensure it is an invalid IOVA. It is safe to reinitialise a domain, but
 * any change which could make prior IOVAs invalid will fail.
 */
int iommu_dma_init_domain(struct iommu_domain *domain, dma_addr_t base,
		u64 size, struct device *dev)
{
	struct iommu_dma_cookie *cookie = domain->iova_cookie;
	struct iova_domain *iovad = &cookie->iovad;
	unsigned long order, base_pfn;
	int attr;

	if (!cookie || cookie->type != IOMMU_DMA_IOVA_COOKIE)
		return -EINVAL;

	/* Use the smallest supported page size for IOVA granularity */
	order = __ffs(domain->pgsize_bitmap);
	base_pfn = max_t(unsigned long, 1, base >> order);

	/* Check the domain allows at least some access to the device... */
	if (domain->geometry.force_aperture) {
		if (base > domain->geometry.aperture_end ||
		    base + size <= domain->geometry.aperture_start) {
			pr_warn("specified DMA range outside IOMMU capability\n");
			return -EFAULT;
		}
		/* ...then finally give it a kicking to make sure it fits */
		base_pfn = max_t(unsigned long, base_pfn,
				domain->geometry.aperture_start >> order);
	}

	/* start_pfn is always nonzero for an already-initialised domain */
	if (iovad->start_pfn) {
		if (1UL << order != iovad->granule ||
		    base_pfn != iovad->start_pfn) {
			pr_warn("Incompatible range for DMA domain\n");
			return -EFAULT;
		}

		return 0;
	}

	init_iova_domain(iovad, 1UL << order, base_pfn);

	if (!cookie->fq_domain && !iommu_domain_get_attr(domain,
			DOMAIN_ATTR_DMA_USE_FLUSH_QUEUE, &attr) && attr) {
		cookie->fq_domain = domain;
		init_iova_flush_queue(iovad, iommu_dma_flush_iotlb_all, NULL);
	}

	if (!dev)
		return 0;

	return iova_reserve_iommu_regions(dev, domain);
}
EXPORT_SYMBOL(iommu_dma_init_domain);

/**
 * dma_info_to_prot - Translate DMA API directions and attributes to IOMMU API
 *                    page flags.
 * @dir: Direction of DMA transfer
 * @coherent: Is the DMA master cache-coherent?
 * @attrs: DMA attributes for the mapping
 *
 * Return: corresponding IOMMU API page protection flags
 */
int dma_info_to_prot(enum dma_data_direction dir, bool coherent,
		     unsigned long attrs)
{
	int prot = coherent ? IOMMU_CACHE : 0;

	if (attrs & DMA_ATTR_PRIVILEGED)
		prot |= IOMMU_PRIV;

	switch (dir) {
	case DMA_BIDIRECTIONAL:
		return prot | IOMMU_READ | IOMMU_WRITE;
	case DMA_TO_DEVICE:
		return prot | IOMMU_READ;
	case DMA_FROM_DEVICE:
		return prot | IOMMU_WRITE;
	default:
		return 0;
	}
}

static dma_addr_t iommu_dma_alloc_iova(struct iommu_domain *domain,
		size_t size, dma_addr_t dma_limit, struct device *dev)
{
	struct iommu_dma_cookie *cookie = domain->iova_cookie;
	struct iova_domain *iovad = &cookie->iovad;
	unsigned long shift, iova_len, iova = 0;

	if (cookie->type == IOMMU_DMA_MSI_COOKIE) {
		cookie->msi_iova += size;
		return cookie->msi_iova - size;
	}

	shift = iova_shift(iovad);
	iova_len = size >> shift;
	/*
	 * Freeing non-power-of-two-sized allocations back into the IOVA caches
	 * will come back to bite us badly, so we have to waste a bit of space
	 * rounding up anything cacheable to make sure that can't happen. The
	 * order of the unadjusted size will still match upon freeing.
	 */
	if (iova_len < (1 << (IOVA_RANGE_CACHE_MAX_SIZE - 1)))
		iova_len = roundup_pow_of_two(iova_len);

	if (dev->bus_dma_mask)
		dma_limit &= dev->bus_dma_mask;

	if (domain->geometry.force_aperture)
		dma_limit = min(dma_limit, domain->geometry.aperture_end);

	/* Try to get PCI devices a SAC address */
	if (dma_limit > DMA_BIT_MASK(32) && dev_is_pci(dev))
		iova = alloc_iova_fast(iovad, iova_len,
				       DMA_BIT_MASK(32) >> shift, false);

	if (!iova)
		iova = alloc_iova_fast(iovad, iova_len, dma_limit >> shift,
				       true);

	return (dma_addr_t)iova << shift;
}

static void iommu_dma_free_iova(struct iommu_dma_cookie *cookie,
		dma_addr_t iova, size_t size)
{
	struct iova_domain *iovad = &cookie->iovad;

	/* The MSI case is only ever cleaning up its most recent allocation */
	if (cookie->type == IOMMU_DMA_MSI_COOKIE)
		cookie->msi_iova -= size;
	else if (cookie->fq_domain)	/* non-strict mode */
		queue_iova(iovad, iova_pfn(iovad, iova),
				size >> iova_shift(iovad), 0);
	else
		free_iova_fast(iovad, iova_pfn(iovad, iova),
				size >> iova_shift(iovad));
}

static void __iommu_dma_unmap(struct iommu_domain *domain, dma_addr_t dma_addr,
		size_t size)
{
	struct iommu_dma_cookie *cookie = domain->iova_cookie;
	struct iova_domain *iovad = &cookie->iovad;
	size_t iova_off = iova_offset(iovad, dma_addr);

	dma_addr -= iova_off;
	size = iova_align(iovad, size + iova_off);

	WARN_ON(iommu_unmap_fast(domain, dma_addr, size) != size);
	if (!cookie->fq_domain)
		iommu_tlb_sync(domain);
	iommu_dma_free_iova(cookie, dma_addr, size);
}

static void __iommu_dma_free_pages(struct page **pages, int count)
{
	while (count--)
		__free_page(pages[count]);
	kvfree(pages);
}

static struct page **__iommu_dma_alloc_pages(struct device *dev,
		unsigned int count, unsigned long order_mask, gfp_t gfp)
{
	struct page **pages;
	unsigned int i = 0, nid = dev_to_node(dev);

	order_mask &= (2U << MAX_ORDER) - 1;
	if (!order_mask)
		return NULL;

	pages = kvzalloc(count * sizeof(*pages), GFP_KERNEL);
	if (!pages)
		return NULL;

	/* IOMMU can map any pages, so himem can also be used here */
	gfp |= __GFP_NOWARN | __GFP_HIGHMEM;

	while (count) {
		struct page *page = NULL;
		unsigned int order_size;

		/*
		 * Higher-order allocations are a convenience rather
		 * than a necessity, hence using __GFP_NORETRY until
		 * falling back to minimum-order allocations.
		 */
		for (order_mask &= (2U << __fls(count)) - 1;
		     order_mask; order_mask &= ~order_size) {
			unsigned int order = __fls(order_mask);
			gfp_t alloc_flags = gfp;

			order_size = 1U << order;
			if (order_mask > order_size)
				alloc_flags |= __GFP_NORETRY;
			page = alloc_pages_node(nid, alloc_flags, order);
			if (!page)
				continue;
			if (!order)
				break;
			if (!PageCompound(page)) {
				split_page(page, order);
				break;
			} else if (!split_huge_page(page)) {
				break;
			}
			__free_pages(page, order);
		}
		if (!page) {
			__iommu_dma_free_pages(pages, i);
			return NULL;
		}
		count -= order_size;
		while (order_size--)
			pages[i++] = page++;
	}
	return pages;
}

/**
 * iommu_dma_free - Free a buffer allocated by iommu_dma_alloc()
 * @dev: Device which owns this buffer
 * @pages: Array of buffer pages as returned by iommu_dma_alloc()
 * @size: Size of buffer in bytes
 * @handle: DMA address of buffer
 *
 * Frees both the pages associated with the buffer, and the array
 * describing them
 */
void iommu_dma_free(struct device *dev, struct page **pages, size_t size,
		dma_addr_t *handle)
{
	__iommu_dma_unmap(iommu_get_dma_domain(dev), *handle, size);
	__iommu_dma_free_pages(pages, PAGE_ALIGN(size) >> PAGE_SHIFT);
	*handle = DMA_MAPPING_ERROR;
}

/**
 * iommu_dma_alloc - Allocate and map a buffer contiguous in IOVA space
 * @dev: Device to allocate memory for. Must be a real device
 *	 attached to an iommu_dma_domain
 * @size: Size of buffer in bytes
 * @gfp: Allocation flags
 * @attrs: DMA attributes for this allocation
 * @prot: IOMMU mapping flags
 * @handle: Out argument for allocated DMA handle
 * @flush_page: Arch callback which must ensure PAGE_SIZE bytes from the
 *		given VA/PA are visible to the given non-coherent device.
 *
 * If @size is less than PAGE_SIZE, then a full CPU page will be allocated,
 * but an IOMMU which supports smaller pages might not map the whole thing.
 *
 * Return: Array of struct page pointers describing the buffer,
 *	   or NULL on failure.
 */
struct page **iommu_dma_alloc(struct device *dev, size_t size, gfp_t gfp,
		unsigned long attrs, int prot, dma_addr_t *handle,
		void (*flush_page)(struct device *, const void *, phys_addr_t))
{
	struct iommu_domain *domain = iommu_get_dma_domain(dev);
	struct iommu_dma_cookie *cookie = domain->iova_cookie;
	struct iova_domain *iovad = &cookie->iovad;
	struct page **pages;
	struct sg_table sgt;
	dma_addr_t iova;
	unsigned int count, min_size, alloc_sizes = domain->pgsize_bitmap;

	*handle = DMA_MAPPING_ERROR;

	min_size = alloc_sizes & -alloc_sizes;
	if (min_size < PAGE_SIZE) {
		min_size = PAGE_SIZE;
		alloc_sizes |= PAGE_SIZE;
	} else {
		size = ALIGN(size, min_size);
	}
	if (attrs & DMA_ATTR_ALLOC_SINGLE_PAGES)
		alloc_sizes = min_size;

	count = PAGE_ALIGN(size) >> PAGE_SHIFT;
	pages = __iommu_dma_alloc_pages(dev, count, alloc_sizes >> PAGE_SHIFT,
					gfp);
	if (!pages)
		return NULL;

	size = iova_align(iovad, size);
	iova = iommu_dma_alloc_iova(domain, size, dev->coherent_dma_mask, dev);
	if (!iova)
		goto out_free_pages;

	if (sg_alloc_table_from_pages(&sgt, pages, count, 0, size, GFP_KERNEL))
		goto out_free_iova;

	if (!(prot & IOMMU_CACHE)) {
		struct sg_mapping_iter miter;
		/*
		 * The CPU-centric flushing implied by SG_MITER_TO_SG isn't
		 * sufficient here, so skip it by using the "wrong" direction.
		 */
		sg_miter_start(&miter, sgt.sgl, sgt.orig_nents, SG_MITER_FROM_SG);
		while (sg_miter_next(&miter))
			flush_page(dev, miter.addr, page_to_phys(miter.page));
		sg_miter_stop(&miter);
	}

	if (iommu_map_sg(domain, iova, sgt.sgl, sgt.orig_nents, prot)
			< size)
		goto out_free_sg;

	*handle = iova;
	sg_free_table(&sgt);
	return pages;

out_free_sg:
	sg_free_table(&sgt);
out_free_iova:
	iommu_dma_free_iova(cookie, iova, size);
out_free_pages:
	__iommu_dma_free_pages(pages, count);
	return NULL;
}

/**
 * iommu_dma_mmap - Map a buffer into provided user VMA
 * @pages: Array representing buffer from iommu_dma_alloc()
 * @size: Size of buffer in bytes
 * @vma: VMA describing requested userspace mapping
 *
 * Maps the pages of the buffer in @pages into @vma. The caller is responsible
 * for verifying the correct size and protection of @vma beforehand.
 */

int iommu_dma_mmap(struct page **pages, size_t size, struct vm_area_struct *vma)
{
	return vm_map_pages(vma, pages, PAGE_ALIGN(size) >> PAGE_SHIFT);
}

static dma_addr_t __iommu_dma_map(struct device *dev, phys_addr_t phys,
		size_t size, int prot, struct iommu_domain *domain)
{
	struct iommu_dma_cookie *cookie = domain->iova_cookie;
	size_t iova_off = 0;
	dma_addr_t iova;

	if (cookie->type == IOMMU_DMA_IOVA_COOKIE) {
		iova_off = iova_offset(&cookie->iovad, phys);
		size = iova_align(&cookie->iovad, size + iova_off);
	}

	iova = iommu_dma_alloc_iova(domain, size, dma_get_mask(dev), dev);
	if (!iova)
		return DMA_MAPPING_ERROR;

	if (iommu_map(domain, iova, phys - iova_off, size, prot)) {
		iommu_dma_free_iova(cookie, iova, size);
		return DMA_MAPPING_ERROR;
	}
	return iova + iova_off;
}

dma_addr_t iommu_dma_map_page(struct device *dev, struct page *page,
		unsigned long offset, size_t size, int prot)
{
	return __iommu_dma_map(dev, page_to_phys(page) + offset, size, prot,
			iommu_get_dma_domain(dev));
}

void iommu_dma_unmap_page(struct device *dev, dma_addr_t handle, size_t size,
		enum dma_data_direction dir, unsigned long attrs)
{
	__iommu_dma_unmap(iommu_get_dma_domain(dev), handle, size);
}

/*
 * Prepare a successfully-mapped scatterlist to give back to the caller.
 *
 * At this point the segments are already laid out by iommu_dma_map_sg() to
 * avoid individually crossing any boundaries, so we merely need to check a
 * segment's start address to avoid concatenating across one.
 */
static int __finalise_sg(struct device *dev, struct scatterlist *sg, int nents,
		dma_addr_t dma_addr)
{
	struct scatterlist *s, *cur = sg;
	unsigned long seg_mask = dma_get_seg_boundary(dev);
	unsigned int cur_len = 0, max_len = dma_get_max_seg_size(dev);
	int i, count = 0;

	for_each_sg(sg, s, nents, i) {
		/* Restore this segment's original unaligned fields first */
		unsigned int s_iova_off = sg_dma_address(s);
		unsigned int s_length = sg_dma_len(s);
		unsigned int s_iova_len = s->length;

		s->offset += s_iova_off;
		s->length = s_length;
		sg_dma_address(s) = DMA_MAPPING_ERROR;
		sg_dma_len(s) = 0;

		/*
		 * Now fill in the real DMA data. If...
		 * - there is a valid output segment to append to
		 * - and this segment starts on an IOVA page boundary
		 * - but doesn't fall at a segment boundary
		 * - and wouldn't make the resulting output segment too long
		 */
		if (cur_len && !s_iova_off && (dma_addr & seg_mask) &&
		    (cur_len + s_length <= max_len)) {
			/* ...then concatenate it with the previous one */
			cur_len += s_length;
		} else {
			/* Otherwise start the next output segment */
			if (i > 0)
				cur = sg_next(cur);
			cur_len = s_length;
			count++;

			sg_dma_address(cur) = dma_addr + s_iova_off;
		}

		sg_dma_len(cur) = cur_len;
		dma_addr += s_iova_len;

		if (s_length + s_iova_off < s_iova_len)
			cur_len = 0;
	}
	return count;
}

/*
 * If mapping failed, then just restore the original list,
 * but making sure the DMA fields are invalidated.
 */
static void __invalidate_sg(struct scatterlist *sg, int nents)
{
	struct scatterlist *s;
	int i;

	for_each_sg(sg, s, nents, i) {
		if (sg_dma_address(s) != DMA_MAPPING_ERROR)
			s->offset += sg_dma_address(s);
		if (sg_dma_len(s))
			s->length = sg_dma_len(s);
		sg_dma_address(s) = DMA_MAPPING_ERROR;
		sg_dma_len(s) = 0;
	}
}

/*
 * The DMA API client is passing in a scatterlist which could describe
 * any old buffer layout, but the IOMMU API requires everything to be
 * aligned to IOMMU pages. Hence the need for this complicated bit of
 * impedance-matching, to be able to hand off a suitably-aligned list,
 * but still preserve the original offsets and sizes for the caller.
 */
int iommu_dma_map_sg(struct device *dev, struct scatterlist *sg,
		int nents, int prot)
{
	struct iommu_domain *domain = iommu_get_dma_domain(dev);
	struct iommu_dma_cookie *cookie = domain->iova_cookie;
	struct iova_domain *iovad = &cookie->iovad;
	struct scatterlist *s, *prev = NULL;
	dma_addr_t iova;
	size_t iova_len = 0;
	unsigned long mask = dma_get_seg_boundary(dev);
	int i;

	/*
	 * Work out how much IOVA space we need, and align the segments to
	 * IOVA granules for the IOMMU driver to handle. With some clever
	 * trickery we can modify the list in-place, but reversibly, by
	 * stashing the unaligned parts in the as-yet-unused DMA fields.
	 */
	for_each_sg(sg, s, nents, i) {
		size_t s_iova_off = iova_offset(iovad, s->offset);
		size_t s_length = s->length;
		size_t pad_len = (mask - iova_len + 1) & mask;

		sg_dma_address(s) = s_iova_off;
		sg_dma_len(s) = s_length;
		s->offset -= s_iova_off;
		s_length = iova_align(iovad, s_length + s_iova_off);
		s->length = s_length;

		/*
		 * Due to the alignment of our single IOVA allocation, we can
		 * depend on these assumptions about the segment boundary mask:
		 * - If mask size >= IOVA size, then the IOVA range cannot
		 *   possibly fall across a boundary, so we don't care.
		 * - If mask size < IOVA size, then the IOVA range must start
		 *   exactly on a boundary, therefore we can lay things out
		 *   based purely on segment lengths without needing to know
		 *   the actual addresses beforehand.
		 * - The mask must be a power of 2, so pad_len == 0 if
		 *   iova_len == 0, thus we cannot dereference prev the first
		 *   time through here (i.e. before it has a meaningful value).
		 */
		if (pad_len && pad_len < s_length - 1) {
			prev->length += pad_len;
			iova_len += pad_len;
		}

		iova_len += s_length;
		prev = s;
	}

	iova = iommu_dma_alloc_iova(domain, iova_len, dma_get_mask(dev), dev);
	if (!iova)
		goto out_restore_sg;

	/*
	 * We'll leave any physical concatenation to the IOMMU driver's
	 * implementation - it knows better than we do.
	 */
	if (iommu_map_sg(domain, iova, sg, nents, prot) < iova_len)
		goto out_free_iova;

	return __finalise_sg(dev, sg, nents, iova);

out_free_iova:
	iommu_dma_free_iova(cookie, iova, iova_len);
out_restore_sg:
	__invalidate_sg(sg, nents);
	return 0;
}

void iommu_dma_unmap_sg(struct device *dev, struct scatterlist *sg, int nents,
		enum dma_data_direction dir, unsigned long attrs)
{
	dma_addr_t start, end;
	struct scatterlist *tmp;
	int i;
	/*
	 * The scatterlist segments are mapped into a single
	 * contiguous IOVA allocation, so this is incredibly easy.
	 */
	start = sg_dma_address(sg);
	for_each_sg(sg_next(sg), tmp, nents - 1, i) {
		if (sg_dma_len(tmp) == 0)
			break;
		sg = tmp;
	}
	end = sg_dma_address(sg) + sg_dma_len(sg);
	__iommu_dma_unmap(iommu_get_dma_domain(dev), start, end - start);
}

dma_addr_t iommu_dma_map_resource(struct device *dev, phys_addr_t phys,
		size_t size, enum dma_data_direction dir, unsigned long attrs)
{
	return __iommu_dma_map(dev, phys, size,
			dma_info_to_prot(dir, false, attrs) | IOMMU_MMIO,
			iommu_get_dma_domain(dev));
}

void iommu_dma_unmap_resource(struct device *dev, dma_addr_t handle,
		size_t size, enum dma_data_direction dir, unsigned long attrs)
{
	__iommu_dma_unmap(iommu_get_dma_domain(dev), handle, size);
}

static struct iommu_dma_msi_page *iommu_dma_get_msi_page(struct device *dev,
		phys_addr_t msi_addr, struct iommu_domain *domain)
{
	struct iommu_dma_cookie *cookie = domain->iova_cookie;
	struct iommu_dma_msi_page *msi_page;
	dma_addr_t iova;
	int prot = IOMMU_WRITE | IOMMU_NOEXEC | IOMMU_MMIO;
	size_t size = cookie_msi_granule(cookie);

	msi_addr &= ~(phys_addr_t)(size - 1);
	list_for_each_entry(msi_page, &cookie->msi_page_list, list)
		if (msi_page->phys == msi_addr)
			return msi_page;

	msi_page = kzalloc(sizeof(*msi_page), GFP_ATOMIC);
	if (!msi_page)
		return NULL;

	iova = __iommu_dma_map(dev, msi_addr, size, prot, domain);
	if (iova == DMA_MAPPING_ERROR)
		goto out_free_page;

	INIT_LIST_HEAD(&msi_page->list);
	msi_page->phys = msi_addr;
	msi_page->iova = iova;
	list_add(&msi_page->list, &cookie->msi_page_list);
	return msi_page;

out_free_page:
	kfree(msi_page);
	return NULL;
}

int iommu_dma_prepare_msi(struct msi_desc *desc, phys_addr_t msi_addr)
{
	struct device *dev = msi_desc_to_dev(desc);
	struct iommu_domain *domain = iommu_get_domain_for_dev(dev);
	struct iommu_dma_cookie *cookie;
	struct iommu_dma_msi_page *msi_page;
	unsigned long flags;

	if (!domain || !domain->iova_cookie) {
		desc->iommu_cookie = NULL;
		return 0;
	}

	cookie = domain->iova_cookie;

	/*
	 * We disable IRQs to rule out a possible inversion against
	 * irq_desc_lock if, say, someone tries to retarget the affinity
	 * of an MSI from within an IPI handler.
	 */
	spin_lock_irqsave(&cookie->msi_lock, flags);
	msi_page = iommu_dma_get_msi_page(dev, msi_addr, domain);
	spin_unlock_irqrestore(&cookie->msi_lock, flags);

	msi_desc_set_iommu_cookie(desc, msi_page);

	if (!msi_page)
		return -ENOMEM;
	return 0;
}

void iommu_dma_compose_msi_msg(struct msi_desc *desc,
			       struct msi_msg *msg)
{
	struct device *dev = msi_desc_to_dev(desc);
	const struct iommu_domain *domain = iommu_get_domain_for_dev(dev);
	const struct iommu_dma_msi_page *msi_page;

	msi_page = msi_desc_get_iommu_cookie(desc);

	if (!domain || !domain->iova_cookie || WARN_ON(!msi_page))
		return;

	msg->address_hi = upper_32_bits(msi_page->iova);
	msg->address_lo &= cookie_msi_granule(domain->iova_cookie) - 1;
	msg->address_lo += lower_32_bits(msi_page->iova);
}