/*
 * VFIO: IOMMU DMA mapping support for Type1 IOMMU
 *
 * Copyright (C) 2012 Red Hat, Inc.  All rights reserved.
 *     Author: Alex Williamson <alex.williamson@redhat.com>
 *
 * 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.
 *
 * Derived from original vfio:
 * Copyright 2010 Cisco Systems, Inc.  All rights reserved.
 * Author: Tom Lyon, pugs@cisco.com
 *
 * We arbitrarily define a Type1 IOMMU as one matching the below code.
 * It could be called the x86 IOMMU as it's designed for AMD-Vi & Intel
 * VT-d, but that makes it harder to re-use as theoretically anyone
 * implementing a similar IOMMU could make use of this.  We expect the
 * IOMMU to support the IOMMU API and have few to no restrictions around
 * the IOVA range that can be mapped.  The Type1 IOMMU is currently
 * optimized for relatively static mappings of a userspace process with
 * userpsace pages pinned into memory.  We also assume devices and IOMMU
 * domains are PCI based as the IOMMU API is still centered around a
 * device/bus interface rather than a group interface.
 */

#include <linux/compat.h>
#include <linux/device.h>
#include <linux/fs.h>
#include <linux/iommu.h>
#include <linux/module.h>
#include <linux/mm.h>
#include <linux/pci.h>          /* pci_bus_type */
#include <linux/sched.h>
#include <linux/slab.h>
#include <linux/uaccess.h>
#include <linux/vfio.h>
#include <linux/workqueue.h>

#define DRIVER_VERSION  "0.2"
#define DRIVER_AUTHOR   "Alex Williamson <alex.williamson@redhat.com>"
#define DRIVER_DESC     "Type1 IOMMU driver for VFIO"

static bool allow_unsafe_interrupts;
module_param_named(allow_unsafe_interrupts,
                   allow_unsafe_interrupts, bool, S_IRUGO | S_IWUSR);
MODULE_PARM_DESC(allow_unsafe_interrupts,
                 "Enable VFIO IOMMU support for on platforms without interrupt remapping support.");

struct vfio_iommu {
        struct iommu_domain     *domain;
        struct mutex            lock;
        struct list_head        dma_list;
        struct list_head        group_list;
        bool                    cache;
};

struct vfio_dma {
        struct list_head        next;
        dma_addr_t              iova;           /* Device address */
        unsigned long           vaddr;          /* Process virtual addr */
        long                    npage;          /* Number of pages */
        int                     prot;           /* IOMMU_READ/WRITE */
};

struct vfio_group {
        struct iommu_group      *iommu_group;
        struct list_head        next;
};

/*
 * This code handles mapping and unmapping of user data buffers
 * into DMA'ble space using the IOMMU
 */

#define NPAGE_TO_SIZE(npage)    ((size_t)(npage) << PAGE_SHIFT)

struct vwork {
        struct mm_struct        *mm;
        long                    npage;
        struct work_struct      work;
};

/* delayed decrement/increment for locked_vm */
static void vfio_lock_acct_bg(struct work_struct *work)
{
        struct vwork *vwork = container_of(work, struct vwork, work);
        struct mm_struct *mm;

        mm = vwork->mm;
        down_write(&mm->mmap_sem);
        mm->locked_vm += vwork->npage;
        up_write(&mm->mmap_sem);
        mmput(mm);
        kfree(vwork);
}

static void vfio_lock_acct(long npage)
{
        struct vwork *vwork;
        struct mm_struct *mm;

        if (!current->mm)
                return; /* process exited */

        if (down_write_trylock(&current->mm->mmap_sem)) {
                current->mm->locked_vm += npage;
                up_write(&current->mm->mmap_sem);
                return;
        }

        /*
         * Couldn't get mmap_sem lock, so must setup to update
         * mm->locked_vm later. If locked_vm were atomic, we
         * wouldn't need this silliness
         */
        vwork = kmalloc(sizeof(struct vwork), GFP_KERNEL);
        if (!vwork)
                return;
        mm = get_task_mm(current);
        if (!mm) {
                kfree(vwork);
                return;
        }
        INIT_WORK(&vwork->work, vfio_lock_acct_bg);
        vwork->mm = mm;
        vwork->npage = npage;
        schedule_work(&vwork->work);
}

/*
 * Some mappings aren't backed by a struct page, for example an mmap'd
 * MMIO range for our own or another device.  These use a different
 * pfn conversion and shouldn't be tracked as locked pages.
 */
static bool is_invalid_reserved_pfn(unsigned long pfn)
{
        if (pfn_valid(pfn)) {
                bool reserved;
                struct page *tail = pfn_to_page(pfn);
                struct page *head = compound_trans_head(tail);
                reserved = !!(PageReserved(head));
                if (head != tail) {
                        /*
                         * "head" is not a dangling pointer
                         * (compound_trans_head takes care of that)
                         * but the hugepage may have been split
                         * from under us (and we may not hold a
                         * reference count on the head page so it can
                         * be reused before we run PageReferenced), so
                         * we've to check PageTail before returning
                         * what we just read.
                         */
                        smp_rmb();
                        if (PageTail(tail))
                                return reserved;
                }
                return PageReserved(tail);
        }

        return true;
}

static int put_pfn(unsigned long pfn, int prot)
{
        if (!is_invalid_reserved_pfn(pfn)) {
                struct page *page = pfn_to_page(pfn);
                if (prot & IOMMU_WRITE)
                        SetPageDirty(page);
                put_page(page);
                return 1;
        }
        return 0;
}

/* Unmap DMA region */
static long __vfio_dma_do_unmap(struct vfio_iommu *iommu, dma_addr_t iova,
                             long npage, int prot)
{
        long i, unlocked = 0;

        for (i = 0; i < npage; i++, iova += PAGE_SIZE) {
                unsigned long pfn;

                pfn = iommu_iova_to_phys(iommu->domain, iova) >> PAGE_SHIFT;
                if (pfn) {
                        iommu_unmap(iommu->domain, iova, PAGE_SIZE);
                        unlocked += put_pfn(pfn, prot);
                }
        }
        return unlocked;
}

static void vfio_dma_unmap(struct vfio_iommu *iommu, dma_addr_t iova,
                           long npage, int prot)
{
        long unlocked;

        unlocked = __vfio_dma_do_unmap(iommu, iova, npage, prot);
        vfio_lock_acct(-unlocked);
}

static int vaddr_get_pfn(unsigned long vaddr, int prot, unsigned long *pfn)
{
        struct page *page[1];
        struct vm_area_struct *vma;
        int ret = -EFAULT;

        if (get_user_pages_fast(vaddr, 1, !!(prot & IOMMU_WRITE), page) == 1) {
                *pfn = page_to_pfn(page[0]);
                return 0;
        }

        down_read(&current->mm->mmap_sem);

        vma = find_vma_intersection(current->mm, vaddr, vaddr + 1);

        if (vma && vma->vm_flags & VM_PFNMAP) {
                *pfn = ((vaddr - vma->vm_start) >> PAGE_SHIFT) + vma->vm_pgoff;
                if (is_invalid_reserved_pfn(*pfn))
                        ret = 0;
        }

        up_read(&current->mm->mmap_sem);

        return ret;
}

/* Map DMA region */
static int __vfio_dma_map(struct vfio_iommu *iommu, dma_addr_t iova,
                          unsigned long vaddr, long npage, int prot)
{
        dma_addr_t start = iova;
        long i, locked = 0;
        int ret;

        /* Verify that pages are not already mapped */
        for (i = 0; i < npage; i++, iova += PAGE_SIZE)
                if (iommu_iova_to_phys(iommu->domain, iova))
                        return -EBUSY;

        iova = start;

        if (iommu->cache)
                prot |= IOMMU_CACHE;

        /*
         * XXX We break mappings into pages and use get_user_pages_fast to
         * pin the pages in memory.  It's been suggested that mlock might
         * provide a more efficient mechanism, but nothing prevents the
         * user from munlocking the pages, which could then allow the user
         * access to random host memory.  We also have no guarantee from the
         * IOMMU API that the iommu driver can unmap sub-pages of previous
         * mappings.  This means we might lose an entire range if a single
         * page within it is unmapped.  Single page mappings are inefficient,
         * but provide the most flexibility for now.
         */
        for (i = 0; i < npage; i++, iova += PAGE_SIZE, vaddr += PAGE_SIZE) {
                unsigned long pfn = 0;

                ret = vaddr_get_pfn(vaddr, prot, &pfn);
                if (ret) {
                        __vfio_dma_do_unmap(iommu, start, i, prot);
                        return ret;
                }

                /*
                 * Only add actual locked pages to accounting
                 * XXX We're effectively marking a page locked for every
                 * IOVA page even though it's possible the user could be
                 * backing multiple IOVAs with the same vaddr.  This over-
                 * penalizes the user process, but we currently have no
                 * easy way to do this properly.
                 */
                if (!is_invalid_reserved_pfn(pfn))
                        locked++;

                ret = iommu_map(iommu->domain, iova,
                                (phys_addr_t)pfn << PAGE_SHIFT,
                                PAGE_SIZE, prot);
                if (ret) {
                        /* Back out mappings on error */
                        put_pfn(pfn, prot);
                        __vfio_dma_do_unmap(iommu, start, i, prot);
                        return ret;
                }
        }
        vfio_lock_acct(locked);
        return 0;
}

static inline bool ranges_overlap(dma_addr_t start1, size_t size1,
                                  dma_addr_t start2, size_t size2)
{
        if (start1 < start2)
                return (start2 - start1 < size1);
        else if (start2 < start1)
                return (start1 - start2 < size2);
        return (size1 > 0 && size2 > 0);
}

static struct vfio_dma *vfio_find_dma(struct vfio_iommu *iommu,
                                                dma_addr_t start, size_t size)
{
        struct vfio_dma *dma;

        list_for_each_entry(dma, &iommu->dma_list, next) {
                if (ranges_overlap(dma->iova, NPAGE_TO_SIZE(dma->npage),
                                   start, size))
                        return dma;
        }
        return NULL;
}

static long vfio_remove_dma_overlap(struct vfio_iommu *iommu, dma_addr_t start,
                                    size_t size, struct vfio_dma *dma)
{
        struct vfio_dma *split;
        long npage_lo, npage_hi;

        /* Existing dma region is completely covered, unmap all */
        if (start <= dma->iova &&
            start + size >= dma->iova + NPAGE_TO_SIZE(dma->npage)) {
                vfio_dma_unmap(iommu, dma->iova, dma->npage, dma->prot);
                list_del(&dma->next);
                npage_lo = dma->npage;
                kfree(dma);
                return npage_lo;
        }

        /* Overlap low address of existing range */
        if (start <= dma->iova) {
                size_t overlap;

                overlap = start + size - dma->iova;
                npage_lo = overlap >> PAGE_SHIFT;

                vfio_dma_unmap(iommu, dma->iova, npage_lo, dma->prot);
                dma->iova += overlap;
                dma->vaddr += overlap;
                dma->npage -= npage_lo;
                return npage_lo;
        }

        /* Overlap high address of existing range */
        if (start + size >= dma->iova + NPAGE_TO_SIZE(dma->npage)) {
                size_t overlap;

                overlap = dma->iova + NPAGE_TO_SIZE(dma->npage) - start;
                npage_hi = overlap >> PAGE_SHIFT;

                vfio_dma_unmap(iommu, start, npage_hi, dma->prot);
                dma->npage -= npage_hi;
                return npage_hi;
        }

        /* Split existing */
        npage_lo = (start - dma->iova) >> PAGE_SHIFT;
        npage_hi = dma->npage - (size >> PAGE_SHIFT) - npage_lo;

        split = kzalloc(sizeof *split, GFP_KERNEL);
        if (!split)
                return -ENOMEM;

        vfio_dma_unmap(iommu, start, size >> PAGE_SHIFT, dma->prot);

        dma->npage = npage_lo;

        split->npage = npage_hi;
        split->iova = start + size;
        split->vaddr = dma->vaddr + NPAGE_TO_SIZE(npage_lo) + size;
        split->prot = dma->prot;
        list_add(&split->next, &iommu->dma_list);
        return size >> PAGE_SHIFT;
}

static int vfio_dma_do_unmap(struct vfio_iommu *iommu,
                             struct vfio_iommu_type1_dma_unmap *unmap)
{
        long ret = 0, npage = unmap->size >> PAGE_SHIFT;
        struct vfio_dma *dma, *tmp;
        uint64_t mask;

        mask = ((uint64_t)1 << __ffs(iommu->domain->ops->pgsize_bitmap)) - 1;

        if (unmap->iova & mask)
                return -EINVAL;
        if (unmap->size & mask)
                return -EINVAL;

        /* XXX We still break these down into PAGE_SIZE */
        WARN_ON(mask & PAGE_MASK);

        mutex_lock(&iommu->lock);

        list_for_each_entry_safe(dma, tmp, &iommu->dma_list, next) {
                if (ranges_overlap(dma->iova, NPAGE_TO_SIZE(dma->npage),
                                   unmap->iova, unmap->size)) {
                        ret = vfio_remove_dma_overlap(iommu, unmap->iova,
                                                      unmap->size, dma);
                        if (ret > 0)
                                npage -= ret;
                        if (ret < 0 || npage == 0)
                                break;
                }
        }
        mutex_unlock(&iommu->lock);
        return ret > 0 ? 0 : (int)ret;
}

static int vfio_dma_do_map(struct vfio_iommu *iommu,
                           struct vfio_iommu_type1_dma_map *map)
{
        struct vfio_dma *dma, *pdma = NULL;
        dma_addr_t iova = map->iova;
        unsigned long locked, lock_limit, vaddr = map->vaddr;
        size_t size = map->size;
        int ret = 0, prot = 0;
        uint64_t mask;
        long npage;

        mask = ((uint64_t)1 << __ffs(iommu->domain->ops->pgsize_bitmap)) - 1;

        /* READ/WRITE from device perspective */
        if (map->flags & VFIO_DMA_MAP_FLAG_WRITE)
                prot |= IOMMU_WRITE;
        if (map->flags & VFIO_DMA_MAP_FLAG_READ)
                prot |= IOMMU_READ;

        if (!prot)
                return -EINVAL; /* No READ/WRITE? */

        if (vaddr & mask)
                return -EINVAL;
        if (iova & mask)
                return -EINVAL;
        if (size & mask)
                return -EINVAL;

        /* XXX We still break these down into PAGE_SIZE */
        WARN_ON(mask & PAGE_MASK);

        /* Don't allow IOVA wrap */
        if (iova + size && iova + size < iova)
                return -EINVAL;

        /* Don't allow virtual address wrap */
        if (vaddr + size && vaddr + size < vaddr)
                return -EINVAL;

        npage = size >> PAGE_SHIFT;
        if (!npage)
                return -EINVAL;

        mutex_lock(&iommu->lock);

        if (vfio_find_dma(iommu, iova, size)) {
                ret = -EBUSY;
                goto out_lock;
        }

        /* account for locked pages */
        locked = current->mm->locked_vm + npage;
        lock_limit = rlimit(RLIMIT_MEMLOCK) >> PAGE_SHIFT;
        if (locked > lock_limit && !capable(CAP_IPC_LOCK)) {
                pr_warn("%s: RLIMIT_MEMLOCK (%ld) exceeded\n",
                        __func__, rlimit(RLIMIT_MEMLOCK));
                ret = -ENOMEM;
                goto out_lock;
        }

        ret = __vfio_dma_map(iommu, iova, vaddr, npage, prot);
        if (ret)
                goto out_lock;

        /* Check if we abut a region below - nothing below 0 */
        if (iova) {
                dma = vfio_find_dma(iommu, iova - 1, 1);
                if (dma && dma->prot == prot &&
                    dma->vaddr + NPAGE_TO_SIZE(dma->npage) == vaddr) {

                        dma->npage += npage;
                        iova = dma->iova;
                        vaddr = dma->vaddr;
                        npage = dma->npage;
                        size = NPAGE_TO_SIZE(npage);

                        pdma = dma;
                }
        }

        /* Check if we abut a region above - nothing above ~0 + 1 */
        if (iova + size) {
                dma = vfio_find_dma(iommu, iova + size, 1);
                if (dma && dma->prot == prot &&
                    dma->vaddr == vaddr + size) {

                        dma->npage += npage;
                        dma->iova = iova;
                        dma->vaddr = vaddr;

                        /*
                         * If merged above and below, remove previously
                         * merged entry.  New entry covers it.
                         */
                        if (pdma) {
                                list_del(&pdma->next);
                                kfree(pdma);
                        }
                        pdma = dma;
                }
        }

        /* Isolated, new region */
        if (!pdma) {
                dma = kzalloc(sizeof *dma, GFP_KERNEL);
                if (!dma) {
                        ret = -ENOMEM;
                        vfio_dma_unmap(iommu, iova, npage, prot);
                        goto out_lock;
                }

                dma->npage = npage;
                dma->iova = iova;
                dma->vaddr = vaddr;
                dma->prot = prot;
                list_add(&dma->next, &iommu->dma_list);
        }

out_lock:
        mutex_unlock(&iommu->lock);
        return ret;
}

static int vfio_iommu_type1_attach_group(void *iommu_data,
                                         struct iommu_group *iommu_group)
{
        struct vfio_iommu *iommu = iommu_data;
        struct vfio_group *group, *tmp;
        int ret;

        group = kzalloc(sizeof(*group), GFP_KERNEL);
        if (!group)
                return -ENOMEM;

        mutex_lock(&iommu->lock);

        list_for_each_entry(tmp, &iommu->group_list, next) {
                if (tmp->iommu_group == iommu_group) {
                        mutex_unlock(&iommu->lock);
                        kfree(group);
                        return -EINVAL;
                }
        }

        /*
         * TODO: Domain have capabilities that might change as we add
         * groups (see iommu->cache, currently never set).  Check for
         * them and potentially disallow groups to be attached when it
         * would change capabilities (ugh).
         */
        ret = iommu_attach_group(iommu->domain, iommu_group);
        if (ret) {
                mutex_unlock(&iommu->lock);
                kfree(group);
                return ret;
        }

        group->iommu_group = iommu_group;
        list_add(&group->next, &iommu->group_list);

        mutex_unlock(&iommu->lock);

        return 0;
}

static void vfio_iommu_type1_detach_group(void *iommu_data,
                                          struct iommu_group *iommu_group)
{
        struct vfio_iommu *iommu = iommu_data;
        struct vfio_group *group;

        mutex_lock(&iommu->lock);

        list_for_each_entry(group, &iommu->group_list, next) {
                if (group->iommu_group == iommu_group) {
                        iommu_detach_group(iommu->domain, iommu_group);
                        list_del(&group->next);
                        kfree(group);
                        break;
                }
        }

        mutex_unlock(&iommu->lock);
}

static void *vfio_iommu_type1_open(unsigned long arg)
{
        struct vfio_iommu *iommu;

        if (arg != VFIO_TYPE1_IOMMU)
                return ERR_PTR(-EINVAL);

        iommu = kzalloc(sizeof(*iommu), GFP_KERNEL);
        if (!iommu)
                return ERR_PTR(-ENOMEM);

        INIT_LIST_HEAD(&iommu->group_list);
        INIT_LIST_HEAD(&iommu->dma_list);
        mutex_init(&iommu->lock);

        /*
         * Wish we didn't have to know about bus_type here.
         */
        iommu->domain = iommu_domain_alloc(&pci_bus_type);
        if (!iommu->domain) {
                kfree(iommu);
                return ERR_PTR(-EIO);
        }

        /*
         * Wish we could specify required capabilities rather than create
         * a domain, see what comes out and hope it doesn't change along
         * the way.  Fortunately we know interrupt remapping is global for
         * our iommus.
         */
        if (!allow_unsafe_interrupts &&
            !iommu_domain_has_cap(iommu->domain, IOMMU_CAP_INTR_REMAP)) {
                pr_warn("%s: No interrupt remapping support.  Use the module param \"allow_unsafe_interrupts\" to enable VFIO IOMMU support on this platform\n",
                       __func__);
                iommu_domain_free(iommu->domain);
                kfree(iommu);
                return ERR_PTR(-EPERM);
        }

        return iommu;
}

static void vfio_iommu_type1_release(void *iommu_data)
{
        struct vfio_iommu *iommu = iommu_data;
        struct vfio_group *group, *group_tmp;
        struct vfio_dma *dma, *dma_tmp;

        list_for_each_entry_safe(group, group_tmp, &iommu->group_list, next) {
                iommu_detach_group(iommu->domain, group->iommu_group);
                list_del(&group->next);
                kfree(group);
        }

        list_for_each_entry_safe(dma, dma_tmp, &iommu->dma_list, next) {
                vfio_dma_unmap(iommu, dma->iova, dma->npage, dma->prot);
                list_del(&dma->next);
                kfree(dma);
        }

        iommu_domain_free(iommu->domain);
        iommu->domain = NULL;
        kfree(iommu);
}

static long vfio_iommu_type1_ioctl(void *iommu_data,
                                   unsigned int cmd, unsigned long arg)
{
        struct vfio_iommu *iommu = iommu_data;
        unsigned long minsz;

        if (cmd == VFIO_CHECK_EXTENSION) {
                switch (arg) {
                case VFIO_TYPE1_IOMMU:
                        return 1;
                default:
                        return 0;
                }
        } else if (cmd == VFIO_IOMMU_GET_INFO) {
                struct vfio_iommu_type1_info info;

                minsz = offsetofend(struct vfio_iommu_type1_info, iova_pgsizes);

                if (copy_from_user(&info, (void __user *)arg, minsz))
                        return -EFAULT;

                if (info.argsz < minsz)
                        return -EINVAL;

                info.flags = 0;

                info.iova_pgsizes = iommu->domain->ops->pgsize_bitmap;

                return copy_to_user((void __user *)arg, &info, minsz);

        } else if (cmd == VFIO_IOMMU_MAP_DMA) {
                struct vfio_iommu_type1_dma_map map;
                uint32_t mask = VFIO_DMA_MAP_FLAG_READ |
                                VFIO_DMA_MAP_FLAG_WRITE;

                minsz = offsetofend(struct vfio_iommu_type1_dma_map, size);

                if (copy_from_user(&map, (void __user *)arg, minsz))
                        return -EFAULT;

                if (map.argsz < minsz || map.flags & ~mask)
                        return -EINVAL;

                return vfio_dma_do_map(iommu, &map);

        } else if (cmd == VFIO_IOMMU_UNMAP_DMA) {
                struct vfio_iommu_type1_dma_unmap unmap;

                minsz = offsetofend(struct vfio_iommu_type1_dma_unmap, size);

                if (copy_from_user(&unmap, (void __user *)arg, minsz))
                        return -EFAULT;

                if (unmap.argsz < minsz || unmap.flags)
                        return -EINVAL;

                return vfio_dma_do_unmap(iommu, &unmap);
        }

        return -ENOTTY;
}

static const struct vfio_iommu_driver_ops vfio_iommu_driver_ops_type1 = {
        .name           = "vfio-iommu-type1",
        .owner          = THIS_MODULE,
        .open           = vfio_iommu_type1_open,
        .release        = vfio_iommu_type1_release,
        .ioctl          = vfio_iommu_type1_ioctl,
        .attach_group   = vfio_iommu_type1_attach_group,
        .detach_group   = vfio_iommu_type1_detach_group,
};

static int __init vfio_iommu_type1_init(void)
{
        if (!iommu_present(&pci_bus_type))
                return -ENODEV;

        return vfio_register_iommu_driver(&vfio_iommu_driver_ops_type1);
}

static void __exit vfio_iommu_type1_cleanup(void)
{
        vfio_unregister_iommu_driver(&vfio_iommu_driver_ops_type1);
}

module_init(vfio_iommu_type1_init);
module_exit(vfio_iommu_type1_cleanup);

MODULE_VERSION(DRIVER_VERSION);
MODULE_LICENSE("GPL v2");
MODULE_AUTHOR(DRIVER_AUTHOR);
MODULE_DESCRIPTION(DRIVER_DESC);