Linux 5.1.15

[linux/fpc-iii.git] / 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 void 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;

        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);
        }
}

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))
                iova_reserve_pci_windows(to_pci_dev(dev), iovad);

        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)
{
        unsigned long uaddr = vma->vm_start;
        unsigned int i, count = PAGE_ALIGN(size) >> PAGE_SHIFT;
        int ret = -ENXIO;

        for (i = vma->vm_pgoff; i < count && uaddr < vma->vm_end; i++) {
                ret = vm_insert_page(vma, uaddr, pages[i]);
                if (ret)
                        break;
                uaddr += PAGE_SIZE;
        }
        return ret;
}

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;
}

void iommu_dma_map_msi_msg(int irq, struct msi_msg *msg)
{
        struct device *dev = msi_desc_to_dev(irq_get_msi_desc(irq));
        struct iommu_domain *domain = iommu_get_domain_for_dev(dev);
        struct iommu_dma_cookie *cookie;
        struct iommu_dma_msi_page *msi_page;
        phys_addr_t msi_addr = (u64)msg->address_hi << 32 | msg->address_lo;
        unsigned long flags;

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

        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);

        if (WARN_ON(!msi_page)) {
                /*
                 * We're called from a void callback, so the best we can do is
                 * 'fail' by filling the message with obviously bogus values.
                 * Since we got this far due to an IOMMU being present, it's
                 * not like the existing address would have worked anyway...
                 */
                msg->address_hi = ~0U;
                msg->address_lo = ~0U;
                msg->data = ~0U;
        } else {
                msg->address_hi = upper_32_bits(msi_page->iova);
                msg->address_lo &= cookie_msi_granule(cookie) - 1;
                msg->address_lo += lower_32_bits(msi_page->iova);
        }
}