Mention branches and keyring.

[releases.git] / gpu / 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"
#include <linux/mmu_context.h>
#include <linux/mmu_notifier.h>
#include <linux/mempolicy.h>
#include <linux/swap.h>
#include <linux/sched/mm.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 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_cached objects;
        struct workqueue_struct *wq;
};

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

static void cancel_userptr(struct work_struct *work)
{
        struct i915_mmu_object *mo = container_of(work, typeof(*mo), work);
        struct drm_i915_gem_object *obj = mo->obj;
        struct work_struct *active;

        /* Cancel any active worker and force us to re-evaluate gup */
        mutex_lock(&obj->mm.lock);
        active = fetch_and_zero(&obj->userptr.work);
        mutex_unlock(&obj->mm.lock);
        if (active)
                goto out;

        i915_gem_object_wait(obj, I915_WAIT_ALL, MAX_SCHEDULE_TIMEOUT, NULL);

        mutex_lock(&obj->base.dev->struct_mutex);

        /* We are inside a kthread context and can't be interrupted */
        if (i915_gem_object_unbind(obj) == 0)
                __i915_gem_object_put_pages(obj, I915_MM_NORMAL);
        WARN_ONCE(i915_gem_object_has_pages(obj),
                  "Failed to release pages: bind_count=%d, pages_pin_count=%d, pin_global=%d\n",
                  obj->bind_count,
                  atomic_read(&obj->mm.pages_pin_count),
                  obj->pin_global);

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

out:
        i915_gem_object_put(obj);
}

static void add_object(struct i915_mmu_object *mo)
{
        if (mo->attached)
                return;

        interval_tree_insert(&mo->it, &mo->mn->objects);
        mo->attached = true;
}

static void del_object(struct i915_mmu_object *mo)
{
        if (!mo->attached)
                return;

        interval_tree_remove(&mo->it, &mo->mn->objects);
        mo->attached = false;
}

static int i915_gem_userptr_mn_invalidate_range_start(struct mmu_notifier *_mn,
                                                       struct mm_struct *mm,
                                                       unsigned long start,
                                                       unsigned long end,
                                                       bool blockable)
{
        struct i915_mmu_notifier *mn =
                container_of(_mn, struct i915_mmu_notifier, mn);
        struct i915_mmu_object *mo;
        struct interval_tree_node *it;
        LIST_HEAD(cancelled);

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

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

        spin_lock(&mn->lock);
        it = interval_tree_iter_first(&mn->objects, start, end);
        while (it) {
                if (!blockable) {
                        spin_unlock(&mn->lock);
                        return -EAGAIN;
                }
                /* 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.
                 */
                mo = container_of(it, struct i915_mmu_object, it);
                if (kref_get_unless_zero(&mo->obj->base.refcount))
                        queue_work(mn->wq, &mo->work);

                list_add(&mo->link, &cancelled);
                it = interval_tree_iter_next(it, start, end);
        }
        list_for_each_entry(mo, &cancelled, link)
                del_object(mo);
        spin_unlock(&mn->lock);

        if (!list_empty(&cancelled))
                flush_workqueue(mn->wq);

        return 0;
}

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;

        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->wq = alloc_workqueue("i915-userptr-release",
                                 WQ_UNBOUND | WQ_MEM_RECLAIM,
                                 0);
        if (mn->wq == NULL) {
                kfree(mn);
                return ERR_PTR(-ENOMEM);
        }

        return mn;
}

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;

        spin_lock(&mo->mn->lock);
        del_object(mo);
        spin_unlock(&mo->mn->lock);
        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;
        int err = 0;

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

        mn = i915_mmu_notifier_create(mm->mm);
        if (IS_ERR(mn))
                err = PTR_ERR(mn);

        down_write(&mm->mm->mmap_sem);
        mutex_lock(&mm->i915->mm_lock);
        if (mm->mn == NULL && !err) {
                /* Protected by mmap_sem (write-lock) */
                err = __mmu_notifier_register(&mn->mn, mm->mm);
                if (!err) {
                        /* Protected by mm_lock */
                        mm->mn = fetch_and_zero(&mn);
                }
        } else if (mm->mn) {
                /*
                 * Someone else raced and successfully installed the mmu
                 * notifier, we can cancel our own errors.
                 */
                err = 0;
        }
        mutex_unlock(&mm->i915->mm_lock);
        up_write(&mm->mm->mmap_sem);

        if (mn && !IS_ERR(mn)) {
                destroy_workqueue(mn->wq);
                kfree(mn);
        }

        return err ? ERR_PTR(err) : mm->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 (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->obj = obj;
        mo->it.start = obj->userptr.ptr;
        mo->it.last = obj->userptr.ptr + obj->base.size - 1;
        INIT_WORK(&mo->work, cancel_userptr);

        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);
        destroy_workqueue(mn->wq);
        kfree(mn);
}

#else

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 *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->i915 = to_i915(obj->base.dev);

                mm->mm = current->mm;
                mmgrab(current->mm);

                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(&mm->i915->mm_lock);

        INIT_WORK(&mm->work, __i915_mm_struct_free__worker);
        queue_work(mm->i915->mm.userptr_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_mutex(&obj->userptr.mm->kref,
                       __i915_mm_struct_free,
                       &to_i915(obj->base.dev)->mm_lock);
        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, int num_pages)
{
        unsigned int max_segment = i915_sg_segment_size();
        struct sg_table *st;
        unsigned int sg_page_sizes;
        int ret;

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

alloc_table:
        ret = __sg_alloc_table_from_pages(st, pvec, num_pages,
                                          0, num_pages << PAGE_SHIFT,
                                          max_segment,
                                          GFP_KERNEL);
        if (ret) {
                kfree(st);
                return ERR_PTR(ret);
        }

        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 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)
                del_object(obj->userptr.mmu_object);
        else if (!work_pending(&obj->userptr.mmu_object->work))
                add_object(obj->userptr.mmu_object);
        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;
        const int npages = obj->base.size >> PAGE_SHIFT;
        struct page **pvec;
        int pinned, 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;

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

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

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

        mutex_lock(&obj->mm.lock);
        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);

        release_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_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.
         */
        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 int 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;

        /* 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 */
                        pinned = __get_user_pages_fast(obj->userptr.ptr,
                                                       num_pages,
                                                       !i915_gem_object_is_readonly(obj),
                                                       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))
                release_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;

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

        if (obj->mm.madv != I915_MADV_WILLNEED)
                obj->mm.dirty = false;

        i915_gem_gtt_finish_pages(obj, pages);

        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);
                put_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 = {
        .flags = I915_GEM_OBJECT_HAS_STRUCT_PAGE |
                 I915_GEM_OBJECT_IS_SHRINKABLE,
        .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_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;

        if (!args->user_size)
                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) {
                struct i915_hw_ppgtt *ppgtt;

                /*
                 * On almost all of the older hw, we cannot tell the GPU that
                 * a page is readonly.
                 */
                ppgtt = dev_priv->kernel_context->ppgtt;
                if (!ppgtt || !ppgtt->vm.has_read_only)
                        return -ENODEV;
        }

        obj = i915_gem_object_alloc(dev_priv);
        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->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)
{
        mutex_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);
}