WIP FPC-III support

[linux/fpc-iii.git] / drivers / gpu / drm / i915 / gem / i915_gem_userptr.c

/*
 * SPDX-License-Identifier: MIT
 *
 * Copyright © 2012-2014 Intel Corporation
 */

#include <linux/mmu_context.h>
#include <linux/mmu_notifier.h>
#include <linux/mempolicy.h>
#include <linux/swap.h>
#include <linux/sched/mm.h>

#include "i915_drv.h"
#include "i915_gem_ioctls.h"
#include "i915_gem_object.h"
#include "i915_scatterlist.h"

struct i915_mm_struct {
        struct mm_struct *mm;
        struct drm_i915_private *i915;
        struct i915_mmu_notifier *mn;
        struct hlist_node node;
        struct kref kref;
        struct rcu_work 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_cached objects;
        struct i915_mm_struct *mm;
};

struct i915_mmu_object {
        struct i915_mmu_notifier *mn;
        struct drm_i915_gem_object *obj;
        struct interval_tree_node it;
};

static void add_object(struct i915_mmu_object *mo)
{
        GEM_BUG_ON(!RB_EMPTY_NODE(&mo->it.rb));
        interval_tree_insert(&mo->it, &mo->mn->objects);
}

static void del_object(struct i915_mmu_object *mo)
{
        if (RB_EMPTY_NODE(&mo->it.rb))
                return;

        interval_tree_remove(&mo->it, &mo->mn->objects);
        RB_CLEAR_NODE(&mo->it.rb);
}

static void
__i915_gem_userptr_set_active(struct drm_i915_gem_object *obj, bool value)
{
        struct i915_mmu_object *mo = obj->userptr.mmu_object;

        /*
         * 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 (!mo)
                return;

        spin_lock(&mo->mn->lock);
        if (value)
                add_object(mo);
        else
                del_object(mo);
        spin_unlock(&mo->mn->lock);
}

static int
userptr_mn_invalidate_range_start(struct mmu_notifier *_mn,
                                  const struct mmu_notifier_range *range)
{
        struct i915_mmu_notifier *mn =
                container_of(_mn, struct i915_mmu_notifier, mn);
        struct interval_tree_node *it;
        unsigned long end;
        int ret = 0;

        if (RB_EMPTY_ROOT(&mn->objects.rb_root))
                return 0;

        /* interval ranges are inclusive, but invalidate range is exclusive */
        end = range->end - 1;

        spin_lock(&mn->lock);
        it = interval_tree_iter_first(&mn->objects, range->start, end);
        while (it) {
                struct drm_i915_gem_object *obj;

                if (!mmu_notifier_range_blockable(range)) {
                        ret = -EAGAIN;
                        break;
                }

                /*
                 * 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. To prevent that
                 * use-after-free we only acquire a reference on the
                 * object if it is not in the process of being destroyed.
                 */
                obj = container_of(it, struct i915_mmu_object, it)->obj;
                if (!kref_get_unless_zero(&obj->base.refcount)) {
                        it = interval_tree_iter_next(it, range->start, end);
                        continue;
                }
                spin_unlock(&mn->lock);

                ret = i915_gem_object_unbind(obj,
                                             I915_GEM_OBJECT_UNBIND_ACTIVE |
                                             I915_GEM_OBJECT_UNBIND_BARRIER);
                if (ret == 0)
                        ret = __i915_gem_object_put_pages(obj);
                i915_gem_object_put(obj);
                if (ret)
                        return ret;

                spin_lock(&mn->lock);

                /*
                 * As we do not (yet) protect the mmu from concurrent insertion
                 * over this range, there is no guarantee that this search will
                 * terminate given a pathologic workload.
                 */
                it = interval_tree_iter_first(&mn->objects, range->start, end);
        }
        spin_unlock(&mn->lock);

        return ret;

}

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

static struct i915_mmu_notifier *
i915_mmu_notifier_create(struct i915_mm_struct *mm)
{
        struct i915_mmu_notifier *mn;

        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_CACHED;
        mn->mm = mm;

        return mn;
}

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

        mo = fetch_and_zero(&obj->userptr.mmu_object);
        if (!mo)
                return;

        spin_lock(&mo->mn->lock);
        del_object(mo);
        spin_unlock(&mo->mn->lock);
        kfree(mo);
}

static struct i915_mmu_notifier *
i915_mmu_notifier_find(struct i915_mm_struct *mm)
{
        struct i915_mmu_notifier *mn, *old;
        int err;

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

        mn = i915_mmu_notifier_create(mm);
        if (IS_ERR(mn))
                return mn;

        err = mmu_notifier_register(&mn->mn, mm->mm);
        if (err) {
                kfree(mn);
                return ERR_PTR(err);
        }

        old = cmpxchg(&mm->mn, NULL, mn);
        if (old) {
                mmu_notifier_unregister(&mn->mn, mm->mm);
                kfree(mn);
                mn = old;
        }

        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;

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

        if (GEM_WARN_ON(!obj->userptr.mm))
                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)
                return -ENOMEM;

        mo->mn = mn;
        mo->obj = obj;
        mo->it.start = obj->userptr.ptr;
        mo->it.last = obj->userptr.ptr + obj->base.size - 1;
        RB_CLEAR_NODE(&mo->it.rb);

        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

static void
__i915_gem_userptr_set_active(struct drm_i915_gem_object *obj, bool value)
{
}

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

static struct i915_mm_struct *
__i915_mm_struct_find(struct drm_i915_private *i915, struct mm_struct *real)
{
        struct i915_mm_struct *it, *mm = NULL;

        rcu_read_lock();
        hash_for_each_possible_rcu(i915->mm_structs,
                                   it, node,
                                   (unsigned long)real)
                if (it->mm == real && kref_get_unless_zero(&it->kref)) {
                        mm = it;
                        break;
                }
        rcu_read_unlock();

        return mm;
}

static int
i915_gem_userptr_init__mm_struct(struct drm_i915_gem_object *obj)
{
        struct drm_i915_private *i915 = to_i915(obj->base.dev);
        struct i915_mm_struct *mm, *new;
        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.
         */
        mm = __i915_mm_struct_find(i915, current->mm);
        if (mm)
                goto out;

        new = kmalloc(sizeof(*mm), GFP_KERNEL);
        if (!new)
                return -ENOMEM;

        kref_init(&new->kref);
        new->i915 = to_i915(obj->base.dev);
        new->mm = current->mm;
        new->mn = NULL;

        spin_lock(&i915->mm_lock);
        mm = __i915_mm_struct_find(i915, current->mm);
        if (!mm) {
                hash_add_rcu(i915->mm_structs,
                             &new->node,
                             (unsigned long)new->mm);
                mmgrab(current->mm);
                mm = new;
        }
        spin_unlock(&i915->mm_lock);
        if (mm != new)
                kfree(new);

out:
        obj->userptr.mm = mm;
        return ret;
}

static void
__i915_mm_struct_free__worker(struct work_struct *work)
{
        struct i915_mm_struct *mm = container_of(work, typeof(*mm), work.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);

        spin_lock(&mm->i915->mm_lock);
        hash_del_rcu(&mm->node);
        spin_unlock(&mm->i915->mm_lock);

        INIT_RCU_WORK(&mm->work, __i915_mm_struct_free__worker);
        queue_rcu_work(system_wq, &mm->work);
}

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

        kref_put(&obj->userptr.mm->kref, __i915_mm_struct_free);
        obj->userptr.mm = NULL;
}

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

static struct sg_table *
__i915_gem_userptr_alloc_pages(struct drm_i915_gem_object *obj,
                               struct page **pvec, unsigned long num_pages)
{
        unsigned int max_segment = i915_sg_segment_size();
        struct sg_table *st;
        unsigned int sg_page_sizes;
        struct scatterlist *sg;
        int ret;

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

alloc_table:
        sg = __sg_alloc_table_from_pages(st, pvec, num_pages, 0,
                                         num_pages << PAGE_SHIFT, max_segment,
                                         NULL, 0, GFP_KERNEL);
        if (IS_ERR(sg)) {
                kfree(st);
                return ERR_CAST(sg);
        }

        ret = i915_gem_gtt_prepare_pages(obj, st);
        if (ret) {
                sg_free_table(st);

                if (max_segment > PAGE_SIZE) {
                        max_segment = PAGE_SIZE;
                        goto alloc_table;
                }

                kfree(st);
                return ERR_PTR(ret);
        }

        sg_page_sizes = i915_sg_page_sizes(st->sgl);

        __i915_gem_object_set_pages(obj, st, sg_page_sizes);

        return st;
}

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;
        const unsigned long npages = obj->base.size >> PAGE_SHIFT;
        unsigned long pinned;
        struct page **pvec;
        int ret;

        ret = -ENOMEM;
        pinned = 0;

        pvec = kvmalloc_array(npages, sizeof(struct page *), GFP_KERNEL);
        if (pvec != NULL) {
                struct mm_struct *mm = obj->userptr.mm->mm;
                unsigned int flags = 0;
                int locked = 0;

                if (!i915_gem_object_is_readonly(obj))
                        flags |= FOLL_WRITE;

                ret = -EFAULT;
                if (mmget_not_zero(mm)) {
                        while (pinned < npages) {
                                if (!locked) {
                                        mmap_read_lock(mm);
                                        locked = 1;
                                }
                                ret = pin_user_pages_remote
                                        (mm,
                                         obj->userptr.ptr + pinned * PAGE_SIZE,
                                         npages - pinned,
                                         flags,
                                         pvec + pinned, NULL, &locked);
                                if (ret < 0)
                                        break;

                                pinned += ret;
                        }
                        if (locked)
                                mmap_read_unlock(mm);
                        mmput(mm);
                }
        }

        mutex_lock_nested(&obj->mm.lock, I915_MM_GET_PAGES);
        if (obj->userptr.work == &work->work) {
                struct sg_table *pages = ERR_PTR(ret);

                if (pinned == npages) {
                        pages = __i915_gem_userptr_alloc_pages(obj, pvec,
                                                               npages);
                        if (!IS_ERR(pages)) {
                                pinned = 0;
                                pages = NULL;
                        }
                }

                obj->userptr.work = ERR_CAST(pages);
                if (IS_ERR(pages))
                        __i915_gem_userptr_set_active(obj, false);
        }
        mutex_unlock(&obj->mm.lock);

        unpin_user_pages(pvec, pinned);
        kvfree(pvec);

        i915_gem_object_put(obj);
        put_task_struct(work->task);
        kfree(work);
}

static struct sg_table *
__i915_gem_userptr_get_pages_schedule(struct drm_i915_gem_object *obj)
{
        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_lock, and we have
         * a strict lock ordering of mmap_lock, 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.
         */
        work = kmalloc(sizeof(*work), GFP_KERNEL);
        if (work == NULL)
                return ERR_PTR(-ENOMEM);

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

        work->obj = i915_gem_object_get(obj);

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

        INIT_WORK(&work->work, __i915_gem_userptr_get_pages_worker);
        queue_work(to_i915(obj->base.dev)->mm.userptr_wq, &work->work);

        return ERR_PTR(-EAGAIN);
}

static int i915_gem_userptr_get_pages(struct drm_i915_gem_object *obj)
{
        const unsigned long num_pages = obj->base.size >> PAGE_SHIFT;
        struct mm_struct *mm = obj->userptr.mm->mm;
        struct page **pvec;
        struct sg_table *pages;
        bool active;
        int pinned;
        unsigned int gup_flags = 0;

        /* 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 (obj->userptr.work) {
                /* active flag should still be held for the pending work */
                if (IS_ERR(obj->userptr.work))
                        return PTR_ERR(obj->userptr.work);
                else
                        return -EAGAIN;
        }

        pvec = NULL;
        pinned = 0;

        if (mm == current->mm) {
                pvec = kvmalloc_array(num_pages, sizeof(struct page *),
                                      GFP_KERNEL |
                                      __GFP_NORETRY |
                                      __GFP_NOWARN);
                if (pvec) {
                        /* defer to worker if malloc fails */
                        if (!i915_gem_object_is_readonly(obj))
                                gup_flags |= FOLL_WRITE;
                        pinned = pin_user_pages_fast_only(obj->userptr.ptr,
                                                          num_pages, gup_flags,
                                                          pvec);
                }
        }

        active = false;
        if (pinned < 0) {
                pages = ERR_PTR(pinned);
                pinned = 0;
        } else if (pinned < num_pages) {
                pages = __i915_gem_userptr_get_pages_schedule(obj);
                active = pages == ERR_PTR(-EAGAIN);
        } else {
                pages = __i915_gem_userptr_alloc_pages(obj, pvec, num_pages);
                active = !IS_ERR(pages);
        }
        if (active)
                __i915_gem_userptr_set_active(obj, true);

        if (IS_ERR(pages))
                unpin_user_pages(pvec, pinned);
        kvfree(pvec);

        return PTR_ERR_OR_ZERO(pages);
}

static void
i915_gem_userptr_put_pages(struct drm_i915_gem_object *obj,
                           struct sg_table *pages)
{
        struct sgt_iter sgt_iter;
        struct page *page;

        /* Cancel any inflight work and force them to restart their gup */
        obj->userptr.work = NULL;
        __i915_gem_userptr_set_active(obj, false);
        if (!pages)
                return;

        __i915_gem_object_release_shmem(obj, pages, true);
        i915_gem_gtt_finish_pages(obj, pages);

        /*
         * We always mark objects as dirty when they are used by the GPU,
         * just in case. However, if we set the vma as being read-only we know
         * that the object will never have been written to.
         */
        if (i915_gem_object_is_readonly(obj))
                obj->mm.dirty = false;

        for_each_sgt_page(page, sgt_iter, pages) {
                if (obj->mm.dirty && trylock_page(page)) {
                        /*
                         * As this may not be anonymous memory (e.g. shmem)
                         * but exist on a real mapping, we have to lock
                         * the page in order to dirty it -- holding
                         * the page reference is not sufficient to
                         * prevent the inode from being truncated.
                         * Play safe and take the lock.
                         *
                         * However...!
                         *
                         * The mmu-notifier can be invalidated for a
                         * migrate_page, that is alreadying holding the lock
                         * on the page. Such a try_to_unmap() will result
                         * in us calling put_pages() and so recursively try
                         * to lock the page. We avoid that deadlock with
                         * a trylock_page() and in exchange we risk missing
                         * some page dirtying.
                         */
                        set_page_dirty(page);
                        unlock_page(page);
                }

                mark_page_accessed(page);
                unpin_user_page(page);
        }
        obj->mm.dirty = false;

        sg_free_table(pages);
        kfree(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 = {
        .name = "i915_gem_object_userptr",
        .flags = I915_GEM_OBJECT_HAS_STRUCT_PAGE |
                 I915_GEM_OBJECT_IS_SHRINKABLE |
                 I915_GEM_OBJECT_NO_MMAP |
                 I915_GEM_OBJECT_ASYNC_CANCEL,
        .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)
{
        static struct lock_class_key lock_class;
        struct drm_i915_private *dev_priv = to_i915(dev);
        struct drm_i915_gem_userptr *args = data;
        struct drm_i915_gem_object *obj;
        int ret;
        u32 handle;

        if (!HAS_LLC(dev_priv) && !HAS_SNOOP(dev_priv)) {
                /* We cannot support coherent userptr objects on hw without
                 * LLC and broken snooping.
                 */
                return -ENODEV;
        }

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

        /*
         * XXX: There is a prevalence of the assumption that we fit the
         * object's page count inside a 32bit _signed_ variable. Let's document
         * this and catch if we ever need to fix it. In the meantime, if you do
         * spot such a local variable, please consider fixing!
         *
         * Aside from our own locals (for which we have no excuse!):
         * - sg_table embeds unsigned int for num_pages
         * - get_user_pages*() mixed ints with longs
         */

        if (args->user_size >> PAGE_SHIFT > INT_MAX)
                return -E2BIG;

        if (overflows_type(args->user_size, obj->base.size))
                return -E2BIG;

        if (!args->user_size)
                return -EINVAL;

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

        if (!access_ok((char __user *)(unsigned long)args->user_ptr, args->user_size))
                return -EFAULT;

        if (args->flags & I915_USERPTR_READ_ONLY) {
                /*
                 * On almost all of the older hw, we cannot tell the GPU that
                 * a page is readonly.
                 */
                if (!dev_priv->gt.vm->has_read_only)
                        return -ENODEV;
        }

        obj = i915_gem_object_alloc();
        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, &lock_class);
        obj->read_domains = I915_GEM_DOMAIN_CPU;
        obj->write_domain = I915_GEM_DOMAIN_CPU;
        i915_gem_object_set_cache_coherency(obj, I915_CACHE_LLC);

        obj->userptr.ptr = args->user_ptr;
        if (args->flags & I915_USERPTR_READ_ONLY)
                i915_gem_object_set_readonly(obj);

        /* 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 */
        i915_gem_object_put(obj);
        if (ret)
                return ret;

        args->handle = handle;
        return 0;
}

int i915_gem_init_userptr(struct drm_i915_private *dev_priv)
{
        spin_lock_init(&dev_priv->mm_lock);
        hash_init(dev_priv->mm_structs);

        dev_priv->mm.userptr_wq =
                alloc_workqueue("i915-userptr-acquire",
                                WQ_HIGHPRI | WQ_UNBOUND,
                                0);
        if (!dev_priv->mm.userptr_wq)
                return -ENOMEM;

        return 0;
}

void i915_gem_cleanup_userptr(struct drm_i915_private *dev_priv)
{
        destroy_workqueue(dev_priv->mm.userptr_wq);
}