[dragonfly.git] / sys / dev / drm / i915 / i915_gem_userptr.c

/*
 * Copyright © 2012-2014 Intel Corporation
 *
 * Permission is hereby granted, free of charge, to any person obtaining a
 * copy of this software and associated documentation files (the "Software"),
 * to deal in the Software without restriction, including without limitation
 * the rights to use, copy, modify, merge, publish, distribute, sublicense,
 * and/or sell copies of the Software, and to permit persons to whom the
 * Software is furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice (including the next
 * paragraph) shall be included in all copies or substantial portions of the
 * Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
 * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
 * IN THE SOFTWARE.
 *
 */

#include <drm/drmP.h>
#include <drm/i915_drm.h>
#include "i915_drv.h"
#include "i915_trace.h"
#include "intel_drv.h"

struct i915_mm_struct {
        struct mm_struct *mm;
        struct drm_device *dev;
        struct i915_mmu_notifier *mn;
        struct hlist_node node;
        struct kref kref;
        struct work_struct work;
};

#if defined(CONFIG_MMU_NOTIFIER)
#include <linux/interval_tree.h>

struct i915_mmu_notifier {
        spinlock_t lock;
        struct hlist_node node;
        struct mmu_notifier mn;
        struct rb_root objects;
        struct list_head linear;
        bool has_linear;
};

struct i915_mmu_object {
        struct i915_mmu_notifier *mn;
        struct interval_tree_node it;
        struct list_head link;
        struct drm_i915_gem_object *obj;
        struct work_struct work;
        bool active;
        bool is_linear;
};

static void __cancel_userptr__worker(struct work_struct *work)
{
        struct i915_mmu_object *mo = container_of(work, typeof(*mo), work);
        struct drm_i915_gem_object *obj = mo->obj;
        struct drm_device *dev = obj->base.dev;

        mutex_lock(&dev->struct_mutex);
        /* Cancel any active worker and force us to re-evaluate gup */
        obj->userptr.work = NULL;

        if (obj->pages != NULL) {
                struct drm_i915_private *dev_priv = to_i915(dev);
                struct i915_vma *vma, *tmp;
                bool was_interruptible;

                was_interruptible = dev_priv->mm.interruptible;
                dev_priv->mm.interruptible = false;

                list_for_each_entry_safe(vma, tmp, &obj->vma_list, vma_link) {
                        int ret = i915_vma_unbind(vma);
                        WARN_ON(ret && ret != -EIO);
                }
                WARN_ON(i915_gem_object_put_pages(obj));

                dev_priv->mm.interruptible = was_interruptible;
        }

        drm_gem_object_unreference(&obj->base);
        mutex_unlock(&dev->struct_mutex);
}

static unsigned long cancel_userptr(struct i915_mmu_object *mo)
{
        unsigned long end = mo->obj->userptr.ptr + mo->obj->base.size;

        /* The mmu_object is released late when destroying the
         * GEM object so it is entirely possible to gain a
         * reference on an object in the process of being freed
         * since our serialisation is via the spinlock and not
         * the struct_mutex - and consequently use it after it
         * is freed and then double free it.
         */
        if (mo->active && kref_get_unless_zero(&mo->obj->base.refcount)) {
                schedule_work(&mo->work);
                /* only schedule one work packet to avoid the refleak */
                mo->active = false;
        }

        return end;
}

static void i915_gem_userptr_mn_invalidate_range_start(struct mmu_notifier *_mn,
                                                       struct mm_struct *mm,
                                                       unsigned long start,
                                                       unsigned long end)
{
        struct i915_mmu_notifier *mn =
                container_of(_mn, struct i915_mmu_notifier, mn);
        struct i915_mmu_object *mo;

        /* interval ranges are inclusive, but invalidate range is exclusive */
        end--;

        spin_lock(&mn->lock);
        if (mn->has_linear) {
                list_for_each_entry(mo, &mn->linear, link) {
                        if (mo->it.last < start || mo->it.start > end)
                                continue;

                        cancel_userptr(mo);
                }
        } else {
                struct interval_tree_node *it;

                it = interval_tree_iter_first(&mn->objects, start, end);
                while (it) {
                        mo = container_of(it, struct i915_mmu_object, it);
                        start = cancel_userptr(mo);
                        it = interval_tree_iter_next(it, start, end);
                }
        }
        spin_unlock(&mn->lock);
}

static const struct mmu_notifier_ops i915_gem_userptr_notifier = {
        .invalidate_range_start = i915_gem_userptr_mn_invalidate_range_start,
};

static struct i915_mmu_notifier *
i915_mmu_notifier_create(struct mm_struct *mm)
{
        struct i915_mmu_notifier *mn;
        int ret;

        mn = kmalloc(sizeof(*mn), GFP_KERNEL);
        if (mn == NULL)
                return ERR_PTR(-ENOMEM);

        spin_lock_init(&mn->lock);
        mn->mn.ops = &i915_gem_userptr_notifier;
        mn->objects = RB_ROOT;
        INIT_LIST_HEAD(&mn->linear);
        mn->has_linear = false;

         /* Protected by mmap_sem (write-lock) */
        ret = __mmu_notifier_register(&mn->mn, mm);
        if (ret) {
                kfree(mn);
                return ERR_PTR(ret);
        }

        return mn;
}

static int
i915_mmu_notifier_add(struct drm_device *dev,
                      struct i915_mmu_notifier *mn,
                      struct i915_mmu_object *mo)
{
        struct interval_tree_node *it;
        int ret = 0;

        /* By this point we have already done a lot of expensive setup that
         * we do not want to repeat just because the caller (e.g. X) has a
         * signal pending (and partly because of that expensive setup, X
         * using an interrupt timer is likely to get stuck in an EINTR loop).
         */
        mutex_lock(&dev->struct_mutex);

        /* Make sure we drop the final active reference (and thereby
         * remove the objects from the interval tree) before we do
         * the check for overlapping objects.
         */
        i915_gem_retire_requests(dev);

        spin_lock(&mn->lock);
        it = interval_tree_iter_first(&mn->objects,
                                      mo->it.start, mo->it.last);
        if (it) {
                struct drm_i915_gem_object *obj;

                /* We only need to check the first object in the range as it
                 * either has cancelled gup work queued and we need to
                 * return back to the user to give time for the gup-workers
                 * to flush their object references upon which the object will
                 * be removed from the interval-tree, or the the range is
                 * still in use by another client and the overlap is invalid.
                 *
                 * If we do have an overlap, we cannot use the interval tree
                 * for fast range invalidation.
                 */

                obj = container_of(it, struct i915_mmu_object, it)->obj;
                if (!obj->userptr.workers)
                        mn->has_linear = mo->is_linear = true;
                else
                        ret = -EAGAIN;
        } else
                interval_tree_insert(&mo->it, &mn->objects);

        if (ret == 0)
                list_add(&mo->link, &mn->linear);

        spin_unlock(&mn->lock);
        mutex_unlock(&dev->struct_mutex);

        return ret;
}

static bool i915_mmu_notifier_has_linear(struct i915_mmu_notifier *mn)
{
        struct i915_mmu_object *mo;

        list_for_each_entry(mo, &mn->linear, link)
                if (mo->is_linear)
                        return true;

        return false;
}

static void
i915_mmu_notifier_del(struct i915_mmu_notifier *mn,
                      struct i915_mmu_object *mo)
{
        spin_lock(&mn->lock);
        list_del(&mo->link);
        if (mo->is_linear)
                mn->has_linear = i915_mmu_notifier_has_linear(mn);
        else
                interval_tree_remove(&mo->it, &mn->objects);
        spin_unlock(&mn->lock);
}

static void
i915_gem_userptr_release__mmu_notifier(struct drm_i915_gem_object *obj)
{
        struct i915_mmu_object *mo;

        mo = obj->userptr.mmu_object;
        if (mo == NULL)
                return;

        i915_mmu_notifier_del(mo->mn, mo);
        kfree(mo);

        obj->userptr.mmu_object = NULL;
}

static struct i915_mmu_notifier *
i915_mmu_notifier_find(struct i915_mm_struct *mm)
{
        struct i915_mmu_notifier *mn = mm->mn;

        mn = mm->mn;
        if (mn)
                return mn;

        down_write(&mm->mm->mmap_sem);
        mutex_lock(&to_i915(mm->dev)->mm_lock);
        if ((mn = mm->mn) == NULL) {
                mn = i915_mmu_notifier_create(mm->mm);
                if (!IS_ERR(mn))
                        mm->mn = mn;
        }
        mutex_unlock(&to_i915(mm->dev)->mm_lock);
        up_write(&mm->mm->mmap_sem);

        return mn;
}

static int
i915_gem_userptr_init__mmu_notifier(struct drm_i915_gem_object *obj,
                                    unsigned flags)
{
        struct i915_mmu_notifier *mn;
        struct i915_mmu_object *mo;
        int ret;

        if (flags & I915_USERPTR_UNSYNCHRONIZED)
                return capable(CAP_SYS_ADMIN) ? 0 : -EPERM;

        if (WARN_ON(obj->userptr.mm == NULL))
                return -EINVAL;

        mn = i915_mmu_notifier_find(obj->userptr.mm);
        if (IS_ERR(mn))
                return PTR_ERR(mn);

        mo = kzalloc(sizeof(*mo), GFP_KERNEL);
        if (mo == NULL)
                return -ENOMEM;

        mo->mn = mn;
        mo->it.start = obj->userptr.ptr;
        mo->it.last = mo->it.start + obj->base.size - 1;
        mo->obj = obj;
        INIT_WORK(&mo->work, __cancel_userptr__worker);

        ret = i915_mmu_notifier_add(obj->base.dev, mn, mo);
        if (ret) {
                kfree(mo);
                return ret;
        }

        obj->userptr.mmu_object = mo;
        return 0;
}

static void
i915_mmu_notifier_free(struct i915_mmu_notifier *mn,
                       struct mm_struct *mm)
{
        if (mn == NULL)
                return;

        mmu_notifier_unregister(&mn->mn, mm);
        kfree(mn);
}

#else

#if 0
static void
i915_gem_userptr_release__mmu_notifier(struct drm_i915_gem_object *obj)
{
}

static int
i915_gem_userptr_init__mmu_notifier(struct drm_i915_gem_object *obj,
                                    unsigned flags)
{
        if ((flags & I915_USERPTR_UNSYNCHRONIZED) == 0)
                return -ENODEV;

        if (!capable(CAP_SYS_ADMIN))
                return -EPERM;

        return 0;
}

static void
i915_mmu_notifier_free(struct i915_mmu_notifier *mn,
                       struct mm_struct *mm)
{
}
#endif

#endif

#if 0
static struct i915_mm_struct *
__i915_mm_struct_find(struct drm_i915_private *dev_priv, struct mm_struct *real)
{
        struct i915_mm_struct *mm;

        /* Protected by dev_priv->mm_lock */
        hash_for_each_possible(dev_priv->mm_structs, mm, node, (unsigned long)real)
                if (mm->mm == real)
                        return mm;

        return NULL;
}

static int
i915_gem_userptr_init__mm_struct(struct drm_i915_gem_object *obj)
{
        struct drm_i915_private *dev_priv = to_i915(obj->base.dev);
        struct i915_mm_struct *mm;
        int ret = 0;

        /* During release of the GEM object we hold the struct_mutex. This
         * precludes us from calling mmput() at that time as that may be
         * the last reference and so call exit_mmap(). exit_mmap() will
         * attempt to reap the vma, and if we were holding a GTT mmap
         * would then call drm_gem_vm_close() and attempt to reacquire
         * the struct mutex. So in order to avoid that recursion, we have
         * to defer releasing the mm reference until after we drop the
         * struct_mutex, i.e. we need to schedule a worker to do the clean
         * up.
         */
        mutex_lock(&dev_priv->mm_lock);
        mm = __i915_mm_struct_find(dev_priv, current->mm);
        if (mm == NULL) {
                mm = kmalloc(sizeof(*mm), GFP_KERNEL);
                if (mm == NULL) {
                        ret = -ENOMEM;
                        goto out;
                }

                kref_init(&mm->kref);
                mm->dev = obj->base.dev;

                mm->mm = current->mm;
                atomic_inc(&current->mm->mm_count);

                mm->mn = NULL;

                /* Protected by dev_priv->mm_lock */
                hash_add(dev_priv->mm_structs,
                         &mm->node, (unsigned long)mm->mm);
        } else
                kref_get(&mm->kref);

        obj->userptr.mm = mm;
out:
        mutex_unlock(&dev_priv->mm_lock);
        return ret;
}

static void
__i915_mm_struct_free__worker(struct work_struct *work)
{
        struct i915_mm_struct *mm = container_of(work, typeof(*mm), work);
        i915_mmu_notifier_free(mm->mn, mm->mm);
        mmdrop(mm->mm);
        kfree(mm);
}

static void
__i915_mm_struct_free(struct kref *kref)
{
        struct i915_mm_struct *mm = container_of(kref, typeof(*mm), kref);

        /* Protected by dev_priv->mm_lock */
        hash_del(&mm->node);
        mutex_unlock(&to_i915(mm->dev)->mm_lock);

        INIT_WORK(&mm->work, __i915_mm_struct_free__worker);
        schedule_work(&mm->work);
}

static void
i915_gem_userptr_release__mm_struct(struct drm_i915_gem_object *obj)
{
        if (obj->userptr.mm == NULL)
                return;

        kref_put_mutex(&obj->userptr.mm->kref,
                       __i915_mm_struct_free,
                       &to_i915(obj->base.dev)->mm_lock);
        obj->userptr.mm = NULL;
}
#endif

struct get_pages_work {
        struct work_struct work;
        struct drm_i915_gem_object *obj;
        struct task_struct *task;
};

#if IS_ENABLED(CONFIG_SWIOTLB)
#define swiotlb_active() swiotlb_nr_tbl()
#else
#define swiotlb_active() 0
#endif

#if 0
static int
st_set_pages(struct sg_table **st, struct page **pvec, int num_pages)
{
        struct scatterlist *sg;
        int ret, n;

        *st = kmalloc(sizeof(**st), GFP_KERNEL);
        if (*st == NULL)
                return -ENOMEM;

        if (swiotlb_active()) {
                ret = sg_alloc_table(*st, num_pages, GFP_KERNEL);
                if (ret)
                        goto err;

                for_each_sg((*st)->sgl, sg, num_pages, n)
                        sg_set_page(sg, pvec[n], PAGE_SIZE, 0);
        } else {
                ret = sg_alloc_table_from_pages(*st, pvec, num_pages,
                                                0, num_pages << PAGE_SHIFT,
                                                GFP_KERNEL);
                if (ret)
                        goto err;
        }

        return 0;

err:
        kfree(*st);
        *st = NULL;
        return ret;
}

static int
__i915_gem_userptr_set_pages(struct drm_i915_gem_object *obj,
                             struct page **pvec, int num_pages)
{
        int ret;

        ret = st_set_pages(&obj->pages, pvec, num_pages);
        if (ret)
                return ret;

        ret = i915_gem_gtt_prepare_object(obj);
        if (ret) {
                sg_free_table(obj->pages);
                kfree(obj->pages);
                obj->pages = NULL;
        }

        return ret;
}

static int
__i915_gem_userptr_set_active(struct drm_i915_gem_object *obj,
                              bool value)
{
        int ret = 0;

        /* During mm_invalidate_range we need to cancel any userptr that
         * overlaps the range being invalidated. Doing so requires the
         * struct_mutex, and that risks recursion. In order to cause
         * recursion, the user must alias the userptr address space with
         * a GTT mmapping (possible with a MAP_FIXED) - then when we have
         * to invalidate that mmaping, mm_invalidate_range is called with
         * the userptr address *and* the struct_mutex held.  To prevent that
         * we set a flag under the i915_mmu_notifier spinlock to indicate
         * whether this object is valid.
         */
#if defined(CONFIG_MMU_NOTIFIER)
        if (obj->userptr.mmu_object == NULL)
                return 0;

        spin_lock(&obj->userptr.mmu_object->mn->lock);
        /* In order to serialise get_pages with an outstanding
         * cancel_userptr, we must drop the struct_mutex and try again.
         */
        if (!value || !work_pending(&obj->userptr.mmu_object->work))
                obj->userptr.mmu_object->active = value;
        else
                ret = -EAGAIN;
        spin_unlock(&obj->userptr.mmu_object->mn->lock);
#endif

        return ret;
}

static void
__i915_gem_userptr_get_pages_worker(struct work_struct *_work)
{
        struct get_pages_work *work = container_of(_work, typeof(*work), work);
        struct drm_i915_gem_object *obj = work->obj;
        struct drm_device *dev = obj->base.dev;
        const int npages = obj->base.size >> PAGE_SHIFT;
        struct page **pvec;
        int pinned, ret;

        ret = -ENOMEM;
        pinned = 0;

        pvec = kmalloc(npages*sizeof(struct page *),
                       GFP_TEMPORARY | __GFP_NOWARN | __GFP_NORETRY);
        if (pvec == NULL)
                pvec = drm_malloc_ab(npages, sizeof(struct page *));
        if (pvec != NULL) {
                struct mm_struct *mm = obj->userptr.mm->mm;

                down_read(&mm->mmap_sem);
                while (pinned < npages) {
                        ret = get_user_pages(work->task, mm,
                                             obj->userptr.ptr + pinned * PAGE_SIZE,
                                             npages - pinned,
                                             !obj->userptr.read_only, 0,
                                             pvec + pinned, NULL);
                        if (ret < 0)
                                break;

                        pinned += ret;
                }
                up_read(&mm->mmap_sem);
        }

        mutex_lock(&dev->struct_mutex);
        if (obj->userptr.work == &work->work) {
                if (pinned == npages) {
                        ret = __i915_gem_userptr_set_pages(obj, pvec, npages);
                        if (ret == 0) {
                                list_add_tail(&obj->global_list,
                                              &to_i915(dev)->mm.unbound_list);
                                obj->get_page.sg = obj->pages->sgl;
                                obj->get_page.last = 0;
                                pinned = 0;
                        }
                }
                obj->userptr.work = ERR_PTR(ret);
                if (ret)
                        __i915_gem_userptr_set_active(obj, false);
        }

        obj->userptr.workers--;
        drm_gem_object_unreference(&obj->base);
        mutex_unlock(&dev->struct_mutex);

        release_pages(pvec, pinned, 0);
        drm_free_large(pvec);

        put_task_struct(work->task);
        kfree(work);
}

static int
__i915_gem_userptr_get_pages_schedule(struct drm_i915_gem_object *obj,
                                      bool *active)
{
        struct get_pages_work *work;

        /* Spawn a worker so that we can acquire the
         * user pages without holding our mutex. Access
         * to the user pages requires mmap_sem, and we have
         * a strict lock ordering of mmap_sem, struct_mutex -
         * we already hold struct_mutex here and so cannot
         * call gup without encountering a lock inversion.
         *
         * Userspace will keep on repeating the operation
         * (thanks to EAGAIN) until either we hit the fast
         * path or the worker completes. If the worker is
         * cancelled or superseded, the task is still run
         * but the results ignored. (This leads to
         * complications that we may have a stray object
         * refcount that we need to be wary of when
         * checking for existing objects during creation.)
         * If the worker encounters an error, it reports
         * that error back to this function through
         * obj->userptr.work = ERR_PTR.
         */
        if (obj->userptr.workers >= I915_GEM_USERPTR_MAX_WORKERS)
                return -EAGAIN;

        work = kmalloc(sizeof(*work), GFP_KERNEL);
        if (work == NULL)
                return -ENOMEM;

        obj->userptr.work = &work->work;
        obj->userptr.workers++;

        work->obj = obj;
        drm_gem_object_reference(&obj->base);

        work->task = current;
        get_task_struct(work->task);

        INIT_WORK(&work->work, __i915_gem_userptr_get_pages_worker);
        schedule_work(&work->work);

        *active = true;
        return -EAGAIN;
}

static int
i915_gem_userptr_get_pages(struct drm_i915_gem_object *obj)
{
        const int num_pages = obj->base.size >> PAGE_SHIFT;
        struct page **pvec;
        int pinned, ret;
        bool active;

        /* If userspace should engineer that these pages are replaced in
         * the vma between us binding this page into the GTT and completion
         * of rendering... Their loss. If they change the mapping of their
         * pages they need to create a new bo to point to the new vma.
         *
         * However, that still leaves open the possibility of the vma
         * being copied upon fork. Which falls under the same userspace
         * synchronisation issue as a regular bo, except that this time
         * the process may not be expecting that a particular piece of
         * memory is tied to the GPU.
         *
         * Fortunately, we can hook into the mmu_notifier in order to
         * discard the page references prior to anything nasty happening
         * to the vma (discard or cloning) which should prevent the more
         * egregious cases from causing harm.
         */
        if (IS_ERR(obj->userptr.work)) {
                /* active flag will have been dropped already by the worker */
                ret = PTR_ERR(obj->userptr.work);
                obj->userptr.work = NULL;
                return ret;
        }
        if (obj->userptr.work)
                /* active flag should still be held for the pending work */
                return -EAGAIN;

        /* Let the mmu-notifier know that we have begun and need cancellation */
        ret = __i915_gem_userptr_set_active(obj, true);
        if (ret)
                return ret;

        pvec = NULL;
        pinned = 0;
        if (obj->userptr.mm->mm == current->mm) {
                pvec = kmalloc(num_pages*sizeof(struct page *),
                               GFP_TEMPORARY | __GFP_NOWARN | __GFP_NORETRY);
                if (pvec == NULL) {
                        pvec = drm_malloc_ab(num_pages, sizeof(struct page *));
                        if (pvec == NULL) {
                                __i915_gem_userptr_set_active(obj, false);
                                return -ENOMEM;
                        }
                }

                pinned = __get_user_pages_fast(obj->userptr.ptr, num_pages,
                                               !obj->userptr.read_only, pvec);
        }

        active = false;
        if (pinned < 0)
                ret = pinned, pinned = 0;
        else if (pinned < num_pages)
                ret = __i915_gem_userptr_get_pages_schedule(obj, &active);
        else
                ret = __i915_gem_userptr_set_pages(obj, pvec, num_pages);
        if (ret) {
                __i915_gem_userptr_set_active(obj, active);
                release_pages(pvec, pinned, 0);
        }
        drm_free_large(pvec);
        return ret;
}

static void
i915_gem_userptr_put_pages(struct drm_i915_gem_object *obj)
{
        struct sg_page_iter sg_iter;

        BUG_ON(obj->userptr.work != NULL);
        __i915_gem_userptr_set_active(obj, false);

        if (obj->madv != I915_MADV_WILLNEED)
                obj->dirty = 0;

        i915_gem_gtt_finish_object(obj);

        for_each_sg_page(obj->pages->sgl, &sg_iter, obj->pages->nents, 0) {
                struct page *page = sg_page_iter_page(&sg_iter);

                if (obj->dirty)
                        set_page_dirty(page);

                mark_page_accessed(page);
                page_cache_release(page);
        }
        obj->dirty = 0;

        sg_free_table(obj->pages);
        kfree(obj->pages);
}

static void
i915_gem_userptr_release(struct drm_i915_gem_object *obj)
{
        i915_gem_userptr_release__mmu_notifier(obj);
        i915_gem_userptr_release__mm_struct(obj);
}

static int
i915_gem_userptr_dmabuf_export(struct drm_i915_gem_object *obj)
{
        if (obj->userptr.mmu_object)
                return 0;

        return i915_gem_userptr_init__mmu_notifier(obj, 0);
}

static const struct drm_i915_gem_object_ops i915_gem_userptr_ops = {
        .flags = I915_GEM_OBJECT_HAS_STRUCT_PAGE,
        .get_pages = i915_gem_userptr_get_pages,
        .put_pages = i915_gem_userptr_put_pages,
        .dmabuf_export = i915_gem_userptr_dmabuf_export,
        .release = i915_gem_userptr_release,
};

/**
 * Creates a new mm object that wraps some normal memory from the process
 * context - user memory.
 *
 * We impose several restrictions upon the memory being mapped
 * into the GPU.
 * 1. It must be page aligned (both start/end addresses, i.e ptr and size).
 * 2. It must be normal system memory, not a pointer into another map of IO
 *    space (e.g. it must not be a GTT mmapping of another object).
 * 3. We only allow a bo as large as we could in theory map into the GTT,
 *    that is we limit the size to the total size of the GTT.
 * 4. The bo is marked as being snoopable. The backing pages are left
 *    accessible directly by the CPU, but reads and writes by the GPU may
 *    incur the cost of a snoop (unless you have an LLC architecture).
 *
 * Synchronisation between multiple users and the GPU is left to userspace
 * through the normal set-domain-ioctl. The kernel will enforce that the
 * GPU relinquishes the VMA before it is returned back to the system
 * i.e. upon free(), munmap() or process termination. However, the userspace
 * malloc() library may not immediately relinquish the VMA after free() and
 * instead reuse it whilst the GPU is still reading and writing to the VMA.
 * Caveat emptor.
 *
 * Also note, that the object created here is not currently a "first class"
 * object, in that several ioctls are banned. These are the CPU access
 * ioctls: mmap(), pwrite and pread. In practice, you are expected to use
 * direct access via your pointer rather than use those ioctls. Another
 * restriction is that we do not allow userptr surfaces to be pinned to the
 * hardware and so we reject any attempt to create a framebuffer out of a
 * userptr.
 *
 * If you think this is a good interface to use to pass GPU memory between
 * drivers, please use dma-buf instead. In fact, wherever possible use
 * dma-buf instead.
 */
int
i915_gem_userptr_ioctl(struct drm_device *dev, void *data, struct drm_file *file)
{
        struct drm_i915_gem_userptr *args = data;
        struct drm_i915_gem_object *obj;
        int ret;
        u32 handle;

        if (args->flags & ~(I915_USERPTR_READ_ONLY |
                            I915_USERPTR_UNSYNCHRONIZED))
                return -EINVAL;

        if (offset_in_page(args->user_ptr | args->user_size))
                return -EINVAL;

        if (!access_ok(args->flags & I915_USERPTR_READ_ONLY ? VERIFY_READ : VERIFY_WRITE,
                       (char __user *)(unsigned long)args->user_ptr, args->user_size))
                return -EFAULT;

        if (args->flags & I915_USERPTR_READ_ONLY) {
                /* On almost all of the current hw, we cannot tell the GPU that a
                 * page is readonly, so this is just a placeholder in the uAPI.
                 */
                return -ENODEV;
        }

        obj = i915_gem_object_alloc(dev);
        if (obj == NULL)
                return -ENOMEM;

        drm_gem_private_object_init(dev, &obj->base, args->user_size);
        i915_gem_object_init(obj, &i915_gem_userptr_ops);
        obj->cache_level = I915_CACHE_LLC;
        obj->base.write_domain = I915_GEM_DOMAIN_CPU;
        obj->base.read_domains = I915_GEM_DOMAIN_CPU;

        obj->userptr.ptr = args->user_ptr;
        obj->userptr.read_only = !!(args->flags & I915_USERPTR_READ_ONLY);

        /* And keep a pointer to the current->mm for resolving the user pages
         * at binding. This means that we need to hook into the mmu_notifier
         * in order to detect if the mmu is destroyed.
         */
        ret = i915_gem_userptr_init__mm_struct(obj);
        if (ret == 0)
                ret = i915_gem_userptr_init__mmu_notifier(obj, args->flags);
        if (ret == 0)
                ret = drm_gem_handle_create(file, &obj->base, &handle);

        /* drop reference from allocate - handle holds it now */
        drm_gem_object_unreference_unlocked(&obj->base);
        if (ret)
                return ret;

        args->handle = handle;
        return 0;
}
#endif

int
i915_gem_init_userptr(struct drm_device *dev)
{
        struct drm_i915_private *dev_priv = to_i915(dev);
        lockinit(&dev_priv->mm_lock, "i915dmm", 0, LK_CANRECURSE);
#if 0
        hash_init(dev_priv->mm_structs);
#endif
        return 0;
}