vfio_iommu_type1.c

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/*
 * VFIO: IOMMU DMA mapping support for Type1 IOMMU
 *
 * Copyright (C) 2012 Red Hat, Inc.  All rights reserved.
 *     Author: Alex Williamson <[email protected]>
 *
 * 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, [email protected]
 *
 * 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 <[email protected]>"
#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);