Merge branch 'for-next' into for-linus

[mirror_ubuntu-hirsute-kernel.git] / drivers / gpu / drm / i915 / gem / i915_gem_mman.c

/*
 * SPDX-License-Identifier: MIT
 *
 * Copyright © 2014-2016 Intel Corporation
 */

#include <linux/anon_inodes.h>
#include <linux/mman.h>
#include <linux/pfn_t.h>
#include <linux/sizes.h>

#include "gt/intel_gt.h"
#include "gt/intel_gt_requests.h"

#include "i915_drv.h"
#include "i915_gem_gtt.h"
#include "i915_gem_ioctls.h"
#include "i915_gem_object.h"
#include "i915_gem_mman.h"
#include "i915_trace.h"
#include "i915_user_extensions.h"
#include "i915_vma.h"

static inline bool
__vma_matches(struct vm_area_struct *vma, struct file *filp,
              unsigned long addr, unsigned long size)
{
        if (vma->vm_file != filp)
                return false;

        return vma->vm_start == addr &&
               (vma->vm_end - vma->vm_start) == PAGE_ALIGN(size);
}

/**
 * i915_gem_mmap_ioctl - Maps the contents of an object, returning the address
 *                       it is mapped to.
 * @dev: drm device
 * @data: ioctl data blob
 * @file: drm file
 *
 * While the mapping holds a reference on the contents of the object, it doesn't
 * imply a ref on the object itself.
 *
 * IMPORTANT:
 *
 * DRM driver writers who look a this function as an example for how to do GEM
 * mmap support, please don't implement mmap support like here. The modern way
 * to implement DRM mmap support is with an mmap offset ioctl (like
 * i915_gem_mmap_gtt) and then using the mmap syscall on the DRM fd directly.
 * That way debug tooling like valgrind will understand what's going on, hiding
 * the mmap call in a driver private ioctl will break that. The i915 driver only
 * does cpu mmaps this way because we didn't know better.
 */
int
i915_gem_mmap_ioctl(struct drm_device *dev, void *data,
                    struct drm_file *file)
{
        struct drm_i915_gem_mmap *args = data;
        struct drm_i915_gem_object *obj;
        unsigned long addr;

        if (args->flags & ~(I915_MMAP_WC))
                return -EINVAL;

        if (args->flags & I915_MMAP_WC && !boot_cpu_has(X86_FEATURE_PAT))
                return -ENODEV;

        obj = i915_gem_object_lookup(file, args->handle);
        if (!obj)
                return -ENOENT;

        /* prime objects have no backing filp to GEM mmap
         * pages from.
         */
        if (!obj->base.filp) {
                addr = -ENXIO;
                goto err;
        }

        if (range_overflows(args->offset, args->size, (u64)obj->base.size)) {
                addr = -EINVAL;
                goto err;
        }

        addr = vm_mmap(obj->base.filp, 0, args->size,
                       PROT_READ | PROT_WRITE, MAP_SHARED,
                       args->offset);
        if (IS_ERR_VALUE(addr))
                goto err;

        if (args->flags & I915_MMAP_WC) {
                struct mm_struct *mm = current->mm;
                struct vm_area_struct *vma;

                if (down_write_killable(&mm->mmap_sem)) {
                        addr = -EINTR;
                        goto err;
                }
                vma = find_vma(mm, addr);
                if (vma && __vma_matches(vma, obj->base.filp, addr, args->size))
                        vma->vm_page_prot =
                                pgprot_writecombine(vm_get_page_prot(vma->vm_flags));
                else
                        addr = -ENOMEM;
                up_write(&mm->mmap_sem);
                if (IS_ERR_VALUE(addr))
                        goto err;
        }
        i915_gem_object_put(obj);

        args->addr_ptr = (u64)addr;
        return 0;

err:
        i915_gem_object_put(obj);
        return addr;
}

static unsigned int tile_row_pages(const struct drm_i915_gem_object *obj)
{
        return i915_gem_object_get_tile_row_size(obj) >> PAGE_SHIFT;
}

/**
 * i915_gem_mmap_gtt_version - report the current feature set for GTT mmaps
 *
 * A history of the GTT mmap interface:
 *
 * 0 - Everything had to fit into the GTT. Both parties of a memcpy had to
 *     aligned and suitable for fencing, and still fit into the available
 *     mappable space left by the pinned display objects. A classic problem
 *     we called the page-fault-of-doom where we would ping-pong between
 *     two objects that could not fit inside the GTT and so the memcpy
 *     would page one object in at the expense of the other between every
 *     single byte.
 *
 * 1 - Objects can be any size, and have any compatible fencing (X Y, or none
 *     as set via i915_gem_set_tiling() [DRM_I915_GEM_SET_TILING]). If the
 *     object is too large for the available space (or simply too large
 *     for the mappable aperture!), a view is created instead and faulted
 *     into userspace. (This view is aligned and sized appropriately for
 *     fenced access.)
 *
 * 2 - Recognise WC as a separate cache domain so that we can flush the
 *     delayed writes via GTT before performing direct access via WC.
 *
 * 3 - Remove implicit set-domain(GTT) and synchronisation on initial
 *     pagefault; swapin remains transparent.
 *
 * 4 - Support multiple fault handlers per object depending on object's
 *     backing storage (a.k.a. MMAP_OFFSET).
 *
 * Restrictions:
 *
 *  * snoopable objects cannot be accessed via the GTT. It can cause machine
 *    hangs on some architectures, corruption on others. An attempt to service
 *    a GTT page fault from a snoopable object will generate a SIGBUS.
 *
 *  * the object must be able to fit into RAM (physical memory, though no
 *    limited to the mappable aperture).
 *
 *
 * Caveats:
 *
 *  * a new GTT page fault will synchronize rendering from the GPU and flush
 *    all data to system memory. Subsequent access will not be synchronized.
 *
 *  * all mappings are revoked on runtime device suspend.
 *
 *  * there are only 8, 16 or 32 fence registers to share between all users
 *    (older machines require fence register for display and blitter access
 *    as well). Contention of the fence registers will cause the previous users
 *    to be unmapped and any new access will generate new page faults.
 *
 *  * running out of memory while servicing a fault may generate a SIGBUS,
 *    rather than the expected SIGSEGV.
 */
int i915_gem_mmap_gtt_version(void)
{
        return 4;
}

static inline struct i915_ggtt_view
compute_partial_view(const struct drm_i915_gem_object *obj,
                     pgoff_t page_offset,
                     unsigned int chunk)
{
        struct i915_ggtt_view view;

        if (i915_gem_object_is_tiled(obj))
                chunk = roundup(chunk, tile_row_pages(obj));

        view.type = I915_GGTT_VIEW_PARTIAL;
        view.partial.offset = rounddown(page_offset, chunk);
        view.partial.size =
                min_t(unsigned int, chunk,
                      (obj->base.size >> PAGE_SHIFT) - view.partial.offset);

        /* If the partial covers the entire object, just create a normal VMA. */
        if (chunk >= obj->base.size >> PAGE_SHIFT)
                view.type = I915_GGTT_VIEW_NORMAL;

        return view;
}

static vm_fault_t i915_error_to_vmf_fault(int err)
{
        switch (err) {
        default:
                WARN_ONCE(err, "unhandled error in %s: %i\n", __func__, err);
                /* fallthrough */
        case -EIO: /* shmemfs failure from swap device */
        case -EFAULT: /* purged object */
        case -ENODEV: /* bad object, how did you get here! */
        case -ENXIO: /* unable to access backing store (on device) */
                return VM_FAULT_SIGBUS;

        case -ENOSPC: /* shmemfs allocation failure */
        case -ENOMEM: /* our allocation failure */
                return VM_FAULT_OOM;

        case 0:
        case -EAGAIN:
        case -ERESTARTSYS:
        case -EINTR:
        case -EBUSY:
                /*
                 * EBUSY is ok: this just means that another thread
                 * already did the job.
                 */
                return VM_FAULT_NOPAGE;
        }
}

static vm_fault_t vm_fault_cpu(struct vm_fault *vmf)
{
        struct vm_area_struct *area = vmf->vma;
        struct i915_mmap_offset *mmo = area->vm_private_data;
        struct drm_i915_gem_object *obj = mmo->obj;
        resource_size_t iomap;
        int err;

        /* Sanity check that we allow writing into this object */
        if (unlikely(i915_gem_object_is_readonly(obj) &&
                     area->vm_flags & VM_WRITE))
                return VM_FAULT_SIGBUS;

        err = i915_gem_object_pin_pages(obj);
        if (err)
                goto out;

        iomap = -1;
        if (!i915_gem_object_type_has(obj, I915_GEM_OBJECT_HAS_STRUCT_PAGE)) {
                iomap = obj->mm.region->iomap.base;
                iomap -= obj->mm.region->region.start;
        }

        /* PTEs are revoked in obj->ops->put_pages() */
        err = remap_io_sg(area,
                          area->vm_start, area->vm_end - area->vm_start,
                          obj->mm.pages->sgl, iomap);

        if (area->vm_flags & VM_WRITE) {
                GEM_BUG_ON(!i915_gem_object_has_pinned_pages(obj));
                obj->mm.dirty = true;
        }

        i915_gem_object_unpin_pages(obj);

out:
        return i915_error_to_vmf_fault(err);
}

static vm_fault_t vm_fault_gtt(struct vm_fault *vmf)
{
#define MIN_CHUNK_PAGES (SZ_1M >> PAGE_SHIFT)
        struct vm_area_struct *area = vmf->vma;
        struct i915_mmap_offset *mmo = area->vm_private_data;
        struct drm_i915_gem_object *obj = mmo->obj;
        struct drm_device *dev = obj->base.dev;
        struct drm_i915_private *i915 = to_i915(dev);
        struct intel_runtime_pm *rpm = &i915->runtime_pm;
        struct i915_ggtt *ggtt = &i915->ggtt;
        bool write = area->vm_flags & VM_WRITE;
        intel_wakeref_t wakeref;
        struct i915_vma *vma;
        pgoff_t page_offset;
        int srcu;
        int ret;

        /* Sanity check that we allow writing into this object */
        if (i915_gem_object_is_readonly(obj) && write)
                return VM_FAULT_SIGBUS;

        /* We don't use vmf->pgoff since that has the fake offset */
        page_offset = (vmf->address - area->vm_start) >> PAGE_SHIFT;

        trace_i915_gem_object_fault(obj, page_offset, true, write);

        ret = i915_gem_object_pin_pages(obj);
        if (ret)
                goto err;

        wakeref = intel_runtime_pm_get(rpm);

        ret = intel_gt_reset_trylock(ggtt->vm.gt, &srcu);
        if (ret)
                goto err_rpm;

        /* Now pin it into the GTT as needed */
        vma = i915_gem_object_ggtt_pin(obj, NULL, 0, 0,
                                       PIN_MAPPABLE |
                                       PIN_NONBLOCK /* NOWARN */ |
                                       PIN_NOEVICT);
        if (IS_ERR(vma)) {
                /* Use a partial view if it is bigger than available space */
                struct i915_ggtt_view view =
                        compute_partial_view(obj, page_offset, MIN_CHUNK_PAGES);
                unsigned int flags;

                flags = PIN_MAPPABLE | PIN_NOSEARCH;
                if (view.type == I915_GGTT_VIEW_NORMAL)
                        flags |= PIN_NONBLOCK; /* avoid warnings for pinned */

                /*
                 * Userspace is now writing through an untracked VMA, abandon
                 * all hope that the hardware is able to track future writes.
                 */

                vma = i915_gem_object_ggtt_pin(obj, &view, 0, 0, flags);
                if (IS_ERR(vma)) {
                        flags = PIN_MAPPABLE;
                        view.type = I915_GGTT_VIEW_PARTIAL;
                        vma = i915_gem_object_ggtt_pin(obj, &view, 0, 0, flags);
                }

                /* The entire mappable GGTT is pinned? Unexpected! */
                GEM_BUG_ON(vma == ERR_PTR(-ENOSPC));
        }
        if (IS_ERR(vma)) {
                ret = PTR_ERR(vma);
                goto err_reset;
        }

        /* Access to snoopable pages through the GTT is incoherent. */
        if (obj->cache_level != I915_CACHE_NONE && !HAS_LLC(i915)) {
                ret = -EFAULT;
                goto err_unpin;
        }

        ret = i915_vma_pin_fence(vma);
        if (ret)
                goto err_unpin;

        /* Finally, remap it using the new GTT offset */
        ret = remap_io_mapping(area,
                               area->vm_start + (vma->ggtt_view.partial.offset << PAGE_SHIFT),
                               (ggtt->gmadr.start + vma->node.start) >> PAGE_SHIFT,
                               min_t(u64, vma->size, area->vm_end - area->vm_start),
                               &ggtt->iomap);
        if (ret)
                goto err_fence;

        assert_rpm_wakelock_held(rpm);

        /* Mark as being mmapped into userspace for later revocation */
        mutex_lock(&i915->ggtt.vm.mutex);
        if (!i915_vma_set_userfault(vma) && !obj->userfault_count++)
                list_add(&obj->userfault_link, &i915->ggtt.userfault_list);
        mutex_unlock(&i915->ggtt.vm.mutex);

        /* Track the mmo associated with the fenced vma */
        vma->mmo = mmo;

        if (IS_ACTIVE(CONFIG_DRM_I915_USERFAULT_AUTOSUSPEND))
                intel_wakeref_auto(&i915->ggtt.userfault_wakeref,
                                   msecs_to_jiffies_timeout(CONFIG_DRM_I915_USERFAULT_AUTOSUSPEND));

        if (write) {
                GEM_BUG_ON(!i915_gem_object_has_pinned_pages(obj));
                i915_vma_set_ggtt_write(vma);
                obj->mm.dirty = true;
        }

err_fence:
        i915_vma_unpin_fence(vma);
err_unpin:
        __i915_vma_unpin(vma);
err_reset:
        intel_gt_reset_unlock(ggtt->vm.gt, srcu);
err_rpm:
        intel_runtime_pm_put(rpm, wakeref);
        i915_gem_object_unpin_pages(obj);
err:
        return i915_error_to_vmf_fault(ret);
}

void __i915_gem_object_release_mmap_gtt(struct drm_i915_gem_object *obj)
{
        struct i915_vma *vma;

        GEM_BUG_ON(!obj->userfault_count);

        for_each_ggtt_vma(vma, obj)
                i915_vma_revoke_mmap(vma);

        GEM_BUG_ON(obj->userfault_count);
}

/*
 * It is vital that we remove the page mapping if we have mapped a tiled
 * object through the GTT and then lose the fence register due to
 * resource pressure. Similarly if the object has been moved out of the
 * aperture, than pages mapped into userspace must be revoked. Removing the
 * mapping will then trigger a page fault on the next user access, allowing
 * fixup by vm_fault_gtt().
 */
static void i915_gem_object_release_mmap_gtt(struct drm_i915_gem_object *obj)
{
        struct drm_i915_private *i915 = to_i915(obj->base.dev);
        intel_wakeref_t wakeref;

        /*
         * Serialisation between user GTT access and our code depends upon
         * revoking the CPU's PTE whilst the mutex is held. The next user
         * pagefault then has to wait until we release the mutex.
         *
         * Note that RPM complicates somewhat by adding an additional
         * requirement that operations to the GGTT be made holding the RPM
         * wakeref.
         */
        wakeref = intel_runtime_pm_get(&i915->runtime_pm);
        mutex_lock(&i915->ggtt.vm.mutex);

        if (!obj->userfault_count)
                goto out;

        __i915_gem_object_release_mmap_gtt(obj);

        /*
         * Ensure that the CPU's PTE are revoked and there are not outstanding
         * memory transactions from userspace before we return. The TLB
         * flushing implied above by changing the PTE above *should* be
         * sufficient, an extra barrier here just provides us with a bit
         * of paranoid documentation about our requirement to serialise
         * memory writes before touching registers / GSM.
         */
        wmb();

out:
        mutex_unlock(&i915->ggtt.vm.mutex);
        intel_runtime_pm_put(&i915->runtime_pm, wakeref);
}

void i915_gem_object_release_mmap_offset(struct drm_i915_gem_object *obj)
{
        struct i915_mmap_offset *mmo;

        spin_lock(&obj->mmo.lock);
        list_for_each_entry(mmo, &obj->mmo.offsets, offset) {
                /*
                 * vma_node_unmap for GTT mmaps handled already in
                 * __i915_gem_object_release_mmap_gtt
                 */
                if (mmo->mmap_type == I915_MMAP_TYPE_GTT)
                        continue;

                spin_unlock(&obj->mmo.lock);
                drm_vma_node_unmap(&mmo->vma_node,
                                   obj->base.dev->anon_inode->i_mapping);
                spin_lock(&obj->mmo.lock);
        }
        spin_unlock(&obj->mmo.lock);
}

/**
 * i915_gem_object_release_mmap - remove physical page mappings
 * @obj: obj in question
 *
 * Preserve the reservation of the mmapping with the DRM core code, but
 * relinquish ownership of the pages back to the system.
 */
void i915_gem_object_release_mmap(struct drm_i915_gem_object *obj)
{
        i915_gem_object_release_mmap_gtt(obj);
        i915_gem_object_release_mmap_offset(obj);
}

static struct i915_mmap_offset *
mmap_offset_attach(struct drm_i915_gem_object *obj,
                   enum i915_mmap_type mmap_type,
                   struct drm_file *file)
{
        struct drm_i915_private *i915 = to_i915(obj->base.dev);
        struct i915_mmap_offset *mmo;
        int err;

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

        mmo->obj = obj;
        mmo->dev = obj->base.dev;
        mmo->file = file;
        mmo->mmap_type = mmap_type;
        drm_vma_node_reset(&mmo->vma_node);

        err = drm_vma_offset_add(mmo->dev->vma_offset_manager, &mmo->vma_node,
                                 obj->base.size / PAGE_SIZE);
        if (likely(!err))
                goto out;

        /* Attempt to reap some mmap space from dead objects */
        err = intel_gt_retire_requests_timeout(&i915->gt, MAX_SCHEDULE_TIMEOUT);
        if (err)
                goto err;

        i915_gem_drain_freed_objects(i915);
        err = drm_vma_offset_add(mmo->dev->vma_offset_manager, &mmo->vma_node,
                                 obj->base.size / PAGE_SIZE);
        if (err)
                goto err;

out:
        if (file)
                drm_vma_node_allow(&mmo->vma_node, file);

        spin_lock(&obj->mmo.lock);
        list_add(&mmo->offset, &obj->mmo.offsets);
        spin_unlock(&obj->mmo.lock);

        return mmo;

err:
        kfree(mmo);
        return ERR_PTR(err);
}

static int
__assign_mmap_offset(struct drm_file *file,
                     u32 handle,
                     enum i915_mmap_type mmap_type,
                     u64 *offset)
{
        struct drm_i915_gem_object *obj;
        struct i915_mmap_offset *mmo;
        int err;

        obj = i915_gem_object_lookup(file, handle);
        if (!obj)
                return -ENOENT;

        if (mmap_type == I915_MMAP_TYPE_GTT &&
            i915_gem_object_never_bind_ggtt(obj)) {
                err = -ENODEV;
                goto out;
        }

        if (mmap_type != I915_MMAP_TYPE_GTT &&
            !i915_gem_object_type_has(obj,
                                      I915_GEM_OBJECT_HAS_STRUCT_PAGE |
                                      I915_GEM_OBJECT_HAS_IOMEM)) {
                err = -ENODEV;
                goto out;
        }

        mmo = mmap_offset_attach(obj, mmap_type, file);
        if (IS_ERR(mmo)) {
                err = PTR_ERR(mmo);
                goto out;
        }

        *offset = drm_vma_node_offset_addr(&mmo->vma_node);
        err = 0;
out:
        i915_gem_object_put(obj);
        return err;
}

int
i915_gem_dumb_mmap_offset(struct drm_file *file,
                          struct drm_device *dev,
                          u32 handle,
                          u64 *offset)
{
        enum i915_mmap_type mmap_type;

        if (boot_cpu_has(X86_FEATURE_PAT))
                mmap_type = I915_MMAP_TYPE_WC;
        else if (!i915_ggtt_has_aperture(&to_i915(dev)->ggtt))
                return -ENODEV;
        else
                mmap_type = I915_MMAP_TYPE_GTT;

        return __assign_mmap_offset(file, handle, mmap_type, offset);
}

/**
 * i915_gem_mmap_offset_ioctl - prepare an object for GTT mmap'ing
 * @dev: DRM device
 * @data: GTT mapping ioctl data
 * @file: GEM object info
 *
 * Simply returns the fake offset to userspace so it can mmap it.
 * The mmap call will end up in drm_gem_mmap(), which will set things
 * up so we can get faults in the handler above.
 *
 * The fault handler will take care of binding the object into the GTT
 * (since it may have been evicted to make room for something), allocating
 * a fence register, and mapping the appropriate aperture address into
 * userspace.
 */
int
i915_gem_mmap_offset_ioctl(struct drm_device *dev, void *data,
                           struct drm_file *file)
{
        struct drm_i915_private *i915 = to_i915(dev);
        struct drm_i915_gem_mmap_offset *args = data;
        enum i915_mmap_type type;
        int err;

        /*
         * Historically we failed to check args.pad and args.offset
         * and so we cannot use those fields for user input and we cannot
         * add -EINVAL for them as the ABI is fixed, i.e. old userspace
         * may be feeding in garbage in those fields.
         *
         * if (args->pad) return -EINVAL; is verbotten!
         */

        err = i915_user_extensions(u64_to_user_ptr(args->extensions),
                                   NULL, 0, NULL);
        if (err)
                return err;

        switch (args->flags) {
        case I915_MMAP_OFFSET_GTT:
                if (!i915_ggtt_has_aperture(&i915->ggtt))
                        return -ENODEV;
                type = I915_MMAP_TYPE_GTT;
                break;

        case I915_MMAP_OFFSET_WC:
                if (!boot_cpu_has(X86_FEATURE_PAT))
                        return -ENODEV;
                type = I915_MMAP_TYPE_WC;
                break;

        case I915_MMAP_OFFSET_WB:
                type = I915_MMAP_TYPE_WB;
                break;

        case I915_MMAP_OFFSET_UC:
                if (!boot_cpu_has(X86_FEATURE_PAT))
                        return -ENODEV;
                type = I915_MMAP_TYPE_UC;
                break;

        default:
                return -EINVAL;
        }

        return __assign_mmap_offset(file, args->handle, type, &args->offset);
}

static void vm_open(struct vm_area_struct *vma)
{
        struct i915_mmap_offset *mmo = vma->vm_private_data;
        struct drm_i915_gem_object *obj = mmo->obj;

        GEM_BUG_ON(!obj);
        i915_gem_object_get(obj);
}

static void vm_close(struct vm_area_struct *vma)
{
        struct i915_mmap_offset *mmo = vma->vm_private_data;
        struct drm_i915_gem_object *obj = mmo->obj;

        GEM_BUG_ON(!obj);
        i915_gem_object_put(obj);
}

static const struct vm_operations_struct vm_ops_gtt = {
        .fault = vm_fault_gtt,
        .open = vm_open,
        .close = vm_close,
};

static const struct vm_operations_struct vm_ops_cpu = {
        .fault = vm_fault_cpu,
        .open = vm_open,
        .close = vm_close,
};

static int singleton_release(struct inode *inode, struct file *file)
{
        struct drm_i915_private *i915 = file->private_data;

        cmpxchg(&i915->gem.mmap_singleton, file, NULL);
        drm_dev_put(&i915->drm);

        return 0;
}

static const struct file_operations singleton_fops = {
        .owner = THIS_MODULE,
        .release = singleton_release,
};

static struct file *mmap_singleton(struct drm_i915_private *i915)
{
        struct file *file;

        rcu_read_lock();
        file = i915->gem.mmap_singleton;
        if (file && !get_file_rcu(file))
                file = NULL;
        rcu_read_unlock();
        if (file)
                return file;

        file = anon_inode_getfile("i915.gem", &singleton_fops, i915, O_RDWR);
        if (IS_ERR(file))
                return file;

        /* Everyone shares a single global address space */
        file->f_mapping = i915->drm.anon_inode->i_mapping;

        smp_store_mb(i915->gem.mmap_singleton, file);
        drm_dev_get(&i915->drm);

        return file;
}

/*
 * This overcomes the limitation in drm_gem_mmap's assignment of a
 * drm_gem_object as the vma->vm_private_data. Since we need to
 * be able to resolve multiple mmap offsets which could be tied
 * to a single gem object.
 */
int i915_gem_mmap(struct file *filp, struct vm_area_struct *vma)
{
        struct drm_vma_offset_node *node;
        struct drm_file *priv = filp->private_data;
        struct drm_device *dev = priv->minor->dev;
        struct i915_mmap_offset *mmo = NULL;
        struct drm_gem_object *obj = NULL;
        struct file *anon;

        if (drm_dev_is_unplugged(dev))
                return -ENODEV;

        drm_vma_offset_lock_lookup(dev->vma_offset_manager);
        node = drm_vma_offset_exact_lookup_locked(dev->vma_offset_manager,
                                                  vma->vm_pgoff,
                                                  vma_pages(vma));
        if (likely(node)) {
                mmo = container_of(node, struct i915_mmap_offset,
                                   vma_node);
                /*
                 * In our dependency chain, the drm_vma_offset_node
                 * depends on the validity of the mmo, which depends on
                 * the gem object. However the only reference we have
                 * at this point is the mmo (as the parent of the node).
                 * Try to check if the gem object was at least cleared.
                 */
                if (!mmo || !mmo->obj) {
                        drm_vma_offset_unlock_lookup(dev->vma_offset_manager);
                        return -EINVAL;
                }
                /*
                 * Skip 0-refcnted objects as it is in the process of being
                 * destroyed and will be invalid when the vma manager lock
                 * is released.
                 */
                obj = &mmo->obj->base;
                if (!kref_get_unless_zero(&obj->refcount))
                        obj = NULL;
        }
        drm_vma_offset_unlock_lookup(dev->vma_offset_manager);
        if (!obj)
                return -EINVAL;

        if (!drm_vma_node_is_allowed(node, priv)) {
                drm_gem_object_put_unlocked(obj);
                return -EACCES;
        }

        if (i915_gem_object_is_readonly(to_intel_bo(obj))) {
                if (vma->vm_flags & VM_WRITE) {
                        drm_gem_object_put_unlocked(obj);
                        return -EINVAL;
                }
                vma->vm_flags &= ~VM_MAYWRITE;
        }

        anon = mmap_singleton(to_i915(obj->dev));
        if (IS_ERR(anon)) {
                drm_gem_object_put_unlocked(obj);
                return PTR_ERR(anon);
        }

        vma->vm_flags |= VM_PFNMAP | VM_DONTEXPAND | VM_DONTDUMP;
        vma->vm_private_data = mmo;

        /*
         * We keep the ref on mmo->obj, not vm_file, but we require
         * vma->vm_file->f_mapping, see vma_link(), for later revocation.
         * Our userspace is accustomed to having per-file resource cleanup
         * (i.e. contexts, objects and requests) on their close(fd), which
         * requires avoiding extraneous references to their filp, hence why
         * we prefer to use an anonymous file for their mmaps.
         */
        fput(vma->vm_file);
        vma->vm_file = anon;

        switch (mmo->mmap_type) {
        case I915_MMAP_TYPE_WC:
                vma->vm_page_prot =
                        pgprot_writecombine(vm_get_page_prot(vma->vm_flags));
                vma->vm_ops = &vm_ops_cpu;
                break;

        case I915_MMAP_TYPE_WB:
                vma->vm_page_prot = vm_get_page_prot(vma->vm_flags);
                vma->vm_ops = &vm_ops_cpu;
                break;

        case I915_MMAP_TYPE_UC:
                vma->vm_page_prot =
                        pgprot_noncached(vm_get_page_prot(vma->vm_flags));
                vma->vm_ops = &vm_ops_cpu;
                break;

        case I915_MMAP_TYPE_GTT:
                vma->vm_page_prot =
                        pgprot_writecombine(vm_get_page_prot(vma->vm_flags));
                vma->vm_ops = &vm_ops_gtt;
                break;
        }
        vma->vm_page_prot = pgprot_decrypted(vma->vm_page_prot);

        return 0;
}

#if IS_ENABLED(CONFIG_DRM_I915_SELFTEST)
#include "selftests/i915_gem_mman.c"
#endif