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Message-ID: <c878204e-c065-4bf4-ba35-edb87bb05914@redhat.com>
Date:   Wed, 1 Nov 2023 21:46:33 +0100
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User-Agent: Mozilla Thunderbird
Subject: Re: [PATCH drm-misc-next v7 4/7] drm/gpuvm: add an abstraction for a
 VM / BO combination
Content-Language: en-US
To:     =?UTF-8?Q?Thomas_Hellstr=C3=B6m?= 
        <thomas.hellstrom@linux.intel.com>, airlied@gmail.com,
        daniel@ffwll.ch, matthew.brost@intel.com, sarah.walker@imgtec.com,
        donald.robson@imgtec.com, boris.brezillon@collabora.com,
        christian.koenig@amd.com, faith@gfxstrand.net
Cc:     nouveau@lists.freedesktop.org, linux-kernel@vger.kernel.org,
        dri-devel@lists.freedesktop.org
References: <20231023201659.25332-1-dakr@redhat.com>
 <20231023201659.25332-5-dakr@redhat.com>
 <f00a4975cf32c3ae28124343a2c994acda083829.camel@linux.intel.com>
 <6fa058a4-20d3-44b9-af58-755cfb375d75@redhat.com>
 <25ac1a025060f7aeb5af363124c6919d7742e8cf.camel@linux.intel.com>
 <8eca7c96-1401-44c0-a150-34221405e3c3@redhat.com>
 <aaf732c6997258dbd06df999626db90256e987e2.camel@linux.intel.com>
From:   Danilo Krummrich <dakr@redhat.com>
Organization: RedHat
In-Reply-To: <aaf732c6997258dbd06df999626db90256e987e2.camel@linux.intel.com>
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On 11/1/23 20:45, Thomas Hellström wrote:
> On Wed, 2023-11-01 at 18:21 +0100, Danilo Krummrich wrote:
>> On 11/1/23 17:38, Thomas Hellström wrote:
>>> On Tue, 2023-10-31 at 18:38 +0100, Danilo Krummrich wrote:
>>>> On 10/31/23 11:32, Thomas Hellström wrote:
>>>>> On Mon, 2023-10-23 at 22:16 +0200, Danilo Krummrich wrote:
>>>>>> Add an abstraction layer between the drm_gpuva mappings of a
>>>>>> particular
>>>>>> drm_gem_object and this GEM object itself. The abstraction
>>>>>> represents
>>>>>> a
>>>>>> combination of a drm_gem_object and drm_gpuvm. The
>>>>>> drm_gem_object
>>>>>> holds
>>>>>> a list of drm_gpuvm_bo structures (the structure representing
>>>>>> this
>>>>>> abstraction), while each drm_gpuvm_bo contains list of
>>>>>> mappings
>>>>>> of
>>>>>> this
>>>>>> GEM object.
>>>>>>
>>>>>> This has multiple advantages:
>>>>>>
>>>>>> 1) We can use the drm_gpuvm_bo structure to attach it to
>>>>>> various
>>>>>> lists
>>>>>>       of the drm_gpuvm. This is useful for tracking external
>>>>>> and
>>>>>> evicted
>>>>>>       objects per VM, which is introduced in subsequent
>>>>>> patches.
>>>>>>
>>>>>> 2) Finding mappings of a certain drm_gem_object mapped in a
>>>>>> certain
>>>>>>       drm_gpuvm becomes much cheaper.
>>>>>>
>>>>>> 3) Drivers can derive and extend the structure to easily
>>>>>> represent
>>>>>>       driver specific states of a BO for a certain GPUVM.
>>>>>>
>>>>>> The idea of this abstraction was taken from amdgpu, hence the
>>>>>> credit
>>>>>> for
>>>>>> this idea goes to the developers of amdgpu.
>>>>>>
>>>>>> Cc: Christian König <christian.koenig@amd.com>
>>>>>> Signed-off-by: Danilo Krummrich <dakr@redhat.com>
>>>>>> ---
>>>>>>     drivers/gpu/drm/drm_gpuvm.c            | 335
>>>>>> +++++++++++++++++++++--
>>>>>> --
>>>>>>     drivers/gpu/drm/nouveau/nouveau_uvmm.c |  64 +++--
>>>>>>     include/drm/drm_gem.h                  |  32 +--
>>>>>>     include/drm/drm_gpuvm.h                | 188
>>>>>> +++++++++++++-
>>>>>>     4 files changed, 533 insertions(+), 86 deletions(-)
>>>>>>
>>>>>> diff --git a/drivers/gpu/drm/drm_gpuvm.c
>>>>>> b/drivers/gpu/drm/drm_gpuvm.c
>>>>>> index c03332883432..7f4f5919f84c 100644
>>>>>> --- a/drivers/gpu/drm/drm_gpuvm.c
>>>>>> +++ b/drivers/gpu/drm/drm_gpuvm.c
>>>>>> @@ -70,6 +70,18 @@
>>>>>>      * &drm_gem_object, such as the &drm_gem_object containing
>>>>>> the
>>>>>> root
>>>>>> page table,
>>>>>>      * but it can also be a 'dummy' object, which can be
>>>>>> allocated
>>>>>> with
>>>>>>      * drm_gpuvm_resv_object_alloc().
>>>>>> + *
>>>>>> + * In order to connect a struct drm_gpuva its backing
>>>>>> &drm_gem_object each
>>>>>> + * &drm_gem_object maintains a list of &drm_gpuvm_bo
>>>>>> structures,
>>>>>> and
>>>>>> each
>>>>>> + * &drm_gpuvm_bo contains a list of &drm_gpuva structures.
>>>>>> + *
>>>>>> + * A &drm_gpuvm_bo is an abstraction that represents a
>>>>>> combination
>>>>>> of a
>>>>>> + * &drm_gpuvm and a &drm_gem_object. Every such combination
>>>>>> should
>>>>>> be unique.
>>>>>> + * This is ensured by the API through drm_gpuvm_bo_obtain()
>>>>>> and
>>>>>> + * drm_gpuvm_bo_obtain_prealloc() which first look into the
>>>>>> corresponding
>>>>>> + * &drm_gem_object list of &drm_gpuvm_bos for an existing
>>>>>> instance
>>>>>> of this
>>>>>> + * particular combination. If not existent a new instance is
>>>>>> created
>>>>>> and linked
>>>>>> + * to the &drm_gem_object.
>>>>>>      */
>>>>>>     
>>>>>>     /**
>>>>>> @@ -395,21 +407,28 @@
>>>>>>     /**
>>>>>>      * DOC: Locking
>>>>>>      *
>>>>>> - * Generally, the GPU VA manager does not take care of
>>>>>> locking
>>>>>> itself, it is
>>>>>> - * the drivers responsibility to take care about locking.
>>>>>> Drivers
>>>>>> might want to
>>>>>> - * protect the following operations: inserting, removing and
>>>>>> iterating
>>>>>> - * &drm_gpuva objects as well as generating all kinds of
>>>>>> operations,
>>>>>> such as
>>>>>> - * split / merge or prefetch.
>>>>>> - *
>>>>>> - * The GPU VA manager also does not take care of the locking
>>>>>> of
>>>>>> the
>>>>>> backing
>>>>>> - * &drm_gem_object buffers GPU VA lists by itself; drivers
>>>>>> are
>>>>>> responsible to
>>>>>> - * enforce mutual exclusion using either the GEMs dma_resv
>>>>>> lock
>>>>>> or
>>>>>> alternatively
>>>>>> - * a driver specific external lock. For the latter see also
>>>>>> - * drm_gem_gpuva_set_lock().
>>>>>> - *
>>>>>> - * However, the GPU VA manager contains lockdep checks to
>>>>>> ensure
>>>>>> callers of its
>>>>>> - * API hold the corresponding lock whenever the
>>>>>> &drm_gem_objects
>>>>>> GPU
>>>>>> VA list is
>>>>>> - * accessed by functions such as drm_gpuva_link() or
>>>>>> drm_gpuva_unlink().
>>>>>> + * In terms of managing &drm_gpuva entries DRM GPUVM does
>>>>>> not
>>>>>> take
>>>>>> care of
>>>>>> + * locking itself, it is the drivers responsibility to take
>>>>>> care
>>>>>> about locking.
>>>>>> + * Drivers might want to protect the following operations:
>>>>>> inserting, removing
>>>>>> + * and iterating &drm_gpuva objects as well as generating
>>>>>> all
>>>>>> kinds
>>>>>> of
>>>>>> + * operations, such as split / merge or prefetch.
>>>>>> + *
>>>>>> + * DRM GPUVM also does not take care of the locking of the
>>>>>> backing
>>>>>> + * &drm_gem_object buffers GPU VA lists and &drm_gpuvm_bo
>>>>>> abstractions by
>>>>>> + * itself; drivers are responsible to enforce mutual
>>>>>> exclusion
>>>>>> using
>>>>>> either the
>>>>>> + * GEMs dma_resv lock or alternatively a driver specific
>>>>>> external
>>>>>> lock. For the
>>>>>> + * latter see also drm_gem_gpuva_set_lock().
>>>>>> + *
>>>>>> + * However, DRM GPUVM contains lockdep checks to ensure
>>>>>> callers
>>>>>> of
>>>>>> its API hold
>>>>>> + * the corresponding lock whenever the &drm_gem_objects GPU
>>>>>> VA
>>>>>> list
>>>>>> is accessed
>>>>>> + * by functions such as drm_gpuva_link() or
>>>>>> drm_gpuva_unlink(),
>>>>>> but
>>>>>> also
>>>>>> + * drm_gpuvm_bo_obtain() and drm_gpuvm_bo_put().
>>>>>> + *
>>>>>> + * The latter is required since on creation and destruction
>>>>>> of a
>>>>>> &drm_gpuvm_bo
>>>>>> + * the &drm_gpuvm_bo is attached / removed from the
>>>>>> &drm_gem_objects
>>>>>> gpuva list.
>>>>>> + * Subsequent calls to drm_gpuvm_bo_obtain() for the same
>>>>>> &drm_gpuvm
>>>>>> and
>>>>>> + * &drm_gem_object must be able to observe previous
>>>>>> creations
>>>>>> and
>>>>>> destructions
>>>>>> + * of &drm_gpuvm_bos in order to keep instances unique.
>>>>>>      */
>>>>>>     
>>>>>>     /**
>>>>>> @@ -439,6 +458,7 @@
>>>>>>      *     {
>>>>>>      *             struct drm_gpuva_ops *ops;
>>>>>>      *             struct drm_gpuva_op *op
>>>>>> + *             struct drm_gpuvm_bo *vm_bo;
>>>>>>      *
>>>>>>      *             driver_lock_va_space();
>>>>>>      *             ops = drm_gpuvm_sm_map_ops_create(gpuvm,
>>>>>> addr,
>>>>>> range,
>>>>>> @@ -446,6 +466,10 @@
>>>>>>      *             if (IS_ERR(ops))
>>>>>>      *                     return PTR_ERR(ops);
>>>>>>      *
>>>>>> + *             vm_bo = drm_gpuvm_bo_obtain(gpuvm, obj);
>>>>>> + *             if (IS_ERR(vm_bo))
>>>>>> + *                     return PTR_ERR(vm_bo);
>>>>>> + *
>>>>>>      *             drm_gpuva_for_each_op(op, ops) {
>>>>>>      *                     struct drm_gpuva *va;
>>>>>>      *
>>>>>> @@ -458,7 +482,7 @@
>>>>>>      *
>>>>>>      *                             driver_vm_map();
>>>>>>      *                             drm_gpuva_map(gpuvm, va,
>>>>>> &op-
>>>>>>> map);
>>>>>> - *                             drm_gpuva_link(va);
>>>>>> + *                             drm_gpuva_link(va, vm_bo);
>>>>>>      *
>>>>>>      *                             break;
>>>>>>      *                     case DRM_GPUVA_OP_REMAP: {
>>>>>> @@ -485,11 +509,11 @@
>>>>>>      *                             driver_vm_remap();
>>>>>>      *                             drm_gpuva_remap(prev, next,
>>>>>> &op-
>>>>>>> remap);
>>>>>>      *
>>>>>> - *                             drm_gpuva_unlink(va);
>>>>>>      *                             if (prev)
>>>>>> - *                                     drm_gpuva_link(prev);
>>>>>> + *                                     drm_gpuva_link(prev,
>>>>>> va-
>>>>>>> vm_bo);
>>>>>>      *                             if (next)
>>>>>> - *                                     drm_gpuva_link(next);
>>>>>> + *                                     drm_gpuva_link(next,
>>>>>> va-
>>>>>>> vm_bo);
>>>>>> + *                             drm_gpuva_unlink(va);
>>>>>>      *
>>>>>>      *                             break;
>>>>>>      *                     }
>>>>>> @@ -505,6 +529,7 @@
>>>>>>      *                             break;
>>>>>>      *                     }
>>>>>>      *             }
>>>>>> + *             drm_gpuvm_bo_put(vm_bo);
>>>>>>      *             driver_unlock_va_space();
>>>>>>      *
>>>>>>      *             return 0;
>>>>>> @@ -514,6 +539,7 @@
>>>>>>      *
>>>>>>      *     struct driver_context {
>>>>>>      *             struct drm_gpuvm *gpuvm;
>>>>>> + *             struct drm_gpuvm_bo *vm_bo;
>>>>>>      *             struct drm_gpuva *new_va;
>>>>>>      *             struct drm_gpuva *prev_va;
>>>>>>      *             struct drm_gpuva *next_va;
>>>>>> @@ -534,6 +560,7 @@
>>>>>>      *                               struct drm_gem_object
>>>>>> *obj,
>>>>>> u64
>>>>>> offset)
>>>>>>      *     {
>>>>>>      *             struct driver_context ctx;
>>>>>> + *             struct drm_gpuvm_bo *vm_bo;
>>>>>>      *             struct drm_gpuva_ops *ops;
>>>>>>      *             struct drm_gpuva_op *op;
>>>>>>      *             int ret = 0;
>>>>>> @@ -543,16 +570,23 @@
>>>>>>      *             ctx.new_va = kzalloc(sizeof(*ctx.new_va),
>>>>>> GFP_KERNEL);
>>>>>>      *             ctx.prev_va = kzalloc(sizeof(*ctx.prev_va),
>>>>>> GFP_KERNEL);
>>>>>>      *             ctx.next_va = kzalloc(sizeof(*ctx.next_va),
>>>>>> GFP_KERNEL);
>>>>>> - *             if (!ctx.new_va || !ctx.prev_va ||
>>>>>> !ctx.next_va)
>>>>>> {
>>>>>> + *             ctx.vm_bo = drm_gpuvm_bo_create(gpuvm, obj);
>>>>>> + *             if (!ctx.new_va || !ctx.prev_va ||
>>>>>> !ctx.next_va
>>>>>>>>
>>>>>> !vm_bo) {
>>>>>>      *                     ret = -ENOMEM;
>>>>>>      *                     goto out;
>>>>>>      *             }
>>>>>>      *
>>>>>> + *             // Typically protected with a driver specific
>>>>>> GEM
>>>>>> gpuva lock
>>>>>> + *             // used in the fence signaling path for
>>>>>> drm_gpuva_link() and
>>>>>> + *             // drm_gpuva_unlink(), hence pre-allocate.
>>>>>> + *             ctx.vm_bo =
>>>>>> drm_gpuvm_bo_obtain_prealloc(ctx.vm_bo);
>>>>>> + *
>>>>>>      *             driver_lock_va_space();
>>>>>>      *             ret = drm_gpuvm_sm_map(gpuvm, &ctx, addr,
>>>>>> range,
>>>>>> obj,
>>>>>> offset);
>>>>>>      *             driver_unlock_va_space();
>>>>>>      *
>>>>>>      *     out:
>>>>>> + *             drm_gpuvm_bo_put(ctx.vm_bo);
>>>>>>      *             kfree(ctx.new_va);
>>>>>>      *             kfree(ctx.prev_va);
>>>>>>      *             kfree(ctx.next_va);
>>>>>> @@ -565,7 +599,7 @@
>>>>>>      *
>>>>>>      *             drm_gpuva_map(ctx->vm, ctx->new_va, &op-
>>>>>>> map);
>>>>>>      *
>>>>>> - *             drm_gpuva_link(ctx->new_va);
>>>>>> + *             drm_gpuva_link(ctx->new_va, ctx->vm_bo);
>>>>>>      *
>>>>>>      *             // prevent the new GPUVA from being freed
>>>>>> in
>>>>>>      *             // driver_mapping_create()
>>>>>> @@ -577,22 +611,23 @@
>>>>>>      *     int driver_gpuva_remap(struct drm_gpuva_op *op,
>>>>>> void
>>>>>> *__ctx)
>>>>>>      *     {
>>>>>>      *             struct driver_context *ctx = __ctx;
>>>>>> + *             struct drm_gpuva *va = op->remap.unmap->va;
>>>>>>      *
>>>>>>      *             drm_gpuva_remap(ctx->prev_va, ctx->next_va,
>>>>>> &op-
>>>>>>> remap);
>>>>>>      *
>>>>>> - *             drm_gpuva_unlink(op->remap.unmap->va);
>>>>>> - *             kfree(op->remap.unmap->va);
>>>>>> - *
>>>>>>      *             if (op->remap.prev) {
>>>>>> - *                     drm_gpuva_link(ctx->prev_va);
>>>>>> + *                     drm_gpuva_link(ctx->prev_va, va-
>>>>>>> vm_bo);
>>>>>>      *                     ctx->prev_va = NULL;
>>>>>>      *             }
>>>>>>      *
>>>>>>      *             if (op->remap.next) {
>>>>>> - *                     drm_gpuva_link(ctx->next_va);
>>>>>> + *                     drm_gpuva_link(ctx->next_va, va-
>>>>>>> vm_bo);
>>>>>>      *                     ctx->next_va = NULL;
>>>>>>      *             }
>>>>>>      *
>>>>>> + *             drm_gpuva_unlink(va);
>>>>>> + *             kfree(va);
>>>>>> + *
>>>>>>      *             return 0;
>>>>>>      *     }
>>>>>>      *
>>>>>> @@ -774,6 +809,194 @@ drm_gpuvm_destroy(struct drm_gpuvm
>>>>>> *gpuvm)
>>>>>>     }
>>>>>>     EXPORT_SYMBOL_GPL(drm_gpuvm_destroy);
>>>>>>     
>>>>>> +/**
>>>>>> + * drm_gpuvm_bo_create() - create a new instance of struct
>>>>>> drm_gpuvm_bo
>>>>>> + * @gpuvm: The &drm_gpuvm the @obj is mapped in.
>>>>>> + * @obj: The &drm_gem_object being mapped in the @gpuvm.
>>>>>> + *
>>>>>> + * If provided by the driver, this function uses the
>>>>>> &drm_gpuvm_ops
>>>>>> + * vm_bo_alloc() callback to allocate.
>>>>>> + *
>>>>>> + * Returns: a pointer to the &drm_gpuvm_bo on success, NULL
>>>>>> on
>>>>>
>>>>> Still needs s/Returns:/Return:/g
>>>>>
>>>>>> failure
>>>>>> + */
>>>>>> +struct drm_gpuvm_bo *
>>>>>> +drm_gpuvm_bo_create(struct drm_gpuvm *gpuvm,
>>>>>> +                   struct drm_gem_object *obj)
>>>>>> +{
>>>>>> +       const struct drm_gpuvm_ops *ops = gpuvm->ops;
>>>>>> +       struct drm_gpuvm_bo *vm_bo;
>>>>>> +
>>>>>> +       if (ops && ops->vm_bo_alloc)
>>>>>> +               vm_bo = ops->vm_bo_alloc();
>>>>>> +       else
>>>>>> +               vm_bo = kzalloc(sizeof(*vm_bo), GFP_KERNEL);
>>>>>> +
>>>>>> +       if (unlikely(!vm_bo))
>>>>>> +               return NULL;
>>>>>> +
>>>>>> +       vm_bo->vm = gpuvm;
>>>>>> +       vm_bo->obj = obj;
>>>>>> +       drm_gem_object_get(obj);
>>>>>> +
>>>>>> +       kref_init(&vm_bo->kref);
>>>>>> +       INIT_LIST_HEAD(&vm_bo->list.gpuva);
>>>>>> +       INIT_LIST_HEAD(&vm_bo->list.entry.gem);
>>>>>> +
>>>>>> +       return vm_bo;
>>>>>> +}
>>>>>> +EXPORT_SYMBOL_GPL(drm_gpuvm_bo_create);
>>>>>> +
>>>>>> +static void
>>>>>> +drm_gpuvm_bo_destroy(struct kref *kref)
>>>>>> +{
>>>>>> +       struct drm_gpuvm_bo *vm_bo = container_of(kref,
>>>>>> struct
>>>>>> drm_gpuvm_bo,
>>>>>> +                                                 kref);
>>>>>> +       struct drm_gpuvm *gpuvm = vm_bo->vm;
>>>>>> +       const struct drm_gpuvm_ops *ops = gpuvm->ops;
>>>>>> +       struct drm_gem_object *obj = vm_bo->obj;
>>>>>> +       bool lock = !drm_gpuvm_resv_protected(gpuvm);
>>>>>> +
>>>>>> +       if (!lock)
>>>>>> +               drm_gpuvm_resv_assert_held(gpuvm);
>>>>>> +
>>>>>> +       drm_gem_gpuva_assert_lock_held(obj);
>>>>>> +       list_del(&vm_bo->list.entry.gem);
>>>>>> +
>>>>>> +       if (ops && ops->vm_bo_free)
>>>>>> +               ops->vm_bo_free(vm_bo);
>>>>>> +       else
>>>>>> +               kfree(vm_bo);
>>>>>> +
>>>>>> +       drm_gem_object_put(obj);
>>>>>> +}
>>>>>> +
>>>>>> +/**
>>>>>> + * drm_gpuvm_bo_put() - drop a struct drm_gpuvm_bo reference
>>>>>> + * @vm_bo: the &drm_gpuvm_bo to release the reference of
>>>>>> + *
>>>>>> + * This releases a reference to @vm_bo.
>>>>>> + *
>>>>>> + * If the reference count drops to zero, the &gpuvm_bo is
>>>>>> destroyed,
>>>>>> which
>>>>>> + * includes removing it from the GEMs gpuva list. Hence, if
>>>>>> a
>>>>>> call
>>>>>> to this
>>>>>> + * function can potentially let the reference count to zero
>>>>>> the
>>>>>> caller must
>>>>>> + * hold the dma-resv or driver specific GEM gpuva lock.
>>>>>> + */
>>>>>> +void
>>>>>> +drm_gpuvm_bo_put(struct drm_gpuvm_bo *vm_bo)
>>>>>> +{
>>>>>> +       if (vm_bo)
>>>>>> +               kref_put(&vm_bo->kref, drm_gpuvm_bo_destroy);
>>>>>> +}
>>>>>> +EXPORT_SYMBOL_GPL(drm_gpuvm_bo_put);
>>>>>> +
>>>>>> +static struct drm_gpuvm_bo *
>>>>>> +__drm_gpuvm_bo_find(struct drm_gpuvm *gpuvm,
>>>>>> +                   struct drm_gem_object *obj)
>>>>>> +{
>>>>>> +       struct drm_gpuvm_bo *vm_bo;
>>>>>> +
>>>>>> +       drm_gem_gpuva_assert_lock_held(obj);
>>>>>> +       drm_gem_for_each_gpuvm_bo(vm_bo, obj)
>>>>>> +               if (vm_bo->vm == gpuvm)
>>>>>> +                       return vm_bo;
>>>>>> +
>>>>>> +       return NULL;
>>>>>> +}
>>>>>> +
>>>>>> +/**
>>>>>> + * drm_gpuvm_bo_find() - find the &drm_gpuvm_bo for the
>>>>>> given
>>>>>> + * &drm_gpuvm and &drm_gem_object
>>>>>> + * @gpuvm: The &drm_gpuvm the @obj is mapped in.
>>>>>> + * @obj: The &drm_gem_object being mapped in the @gpuvm.
>>>>>> + *
>>>>>> + * Find the &drm_gpuvm_bo representing the combination of
>>>>>> the
>>>>>> given
>>>>>> + * &drm_gpuvm and &drm_gem_object. If found, increases the
>>>>>> reference
>>>>>> + * count of the &drm_gpuvm_bo accordingly.
>>>>>> + *
>>>>>> + * Returns: a pointer to the &drm_gpuvm_bo on success, NULL
>>>>>> on
>>>>>> failure
>>>>>> + */
>>>>>> +struct drm_gpuvm_bo *
>>>>>> +drm_gpuvm_bo_find(struct drm_gpuvm *gpuvm,
>>>>>> +                 struct drm_gem_object *obj)
>>>>>> +{
>>>>>> +       struct drm_gpuvm_bo *vm_bo =
>>>>>> __drm_gpuvm_bo_find(gpuvm,
>>>>>> obj);
>>>>>> +
>>>>>> +       return vm_bo ? drm_gpuvm_bo_get(vm_bo) : NULL;
>>>>>> +}
>>>>>> +EXPORT_SYMBOL_GPL(drm_gpuvm_bo_find);
>>>>>> +
>>>>>> +/**
>>>>>> + * drm_gpuvm_bo_obtain() - obtains and instance of the
>>>>>> &drm_gpuvm_bo
>>>>>> for the
>>>>>> + * given &drm_gpuvm and &drm_gem_object
>>>>>> + * @gpuvm: The &drm_gpuvm the @obj is mapped in.
>>>>>> + * @obj: The &drm_gem_object being mapped in the @gpuvm.
>>>>>> + *
>>>>>> + * Find the &drm_gpuvm_bo representing the combination of
>>>>>> the
>>>>>> given
>>>>>> + * &drm_gpuvm and &drm_gem_object. If found, increases the
>>>>>> reference
>>>>>> + * count of the &drm_gpuvm_bo accordingly. If not found,
>>>>>> allocates a
>>>>>> new
>>>>>> + * &drm_gpuvm_bo.
>>>>>> + *
>>>>>> + * A new &drm_gpuvm_bo is added to the GEMs gpuva list.
>>>>>> + *
>>>>>> + * Returns: a pointer to the &drm_gpuvm_bo on success, an
>>>>>> ERR_PTR on
>>>>>> failure
>>>>>> + */
>>>>>> +struct drm_gpuvm_bo *
>>>>>> +drm_gpuvm_bo_obtain(struct drm_gpuvm *gpuvm,
>>>>>> +                   struct drm_gem_object *obj)
>>>>>> +{
>>>>>> +       struct drm_gpuvm_bo *vm_bo;
>>>>>> +
>>>>>> +       vm_bo = drm_gpuvm_bo_find(gpuvm, obj);
>>>>>> +       if (vm_bo)
>>>>>> +               return vm_bo;
>>>>>> +
>>>>>> +       vm_bo = drm_gpuvm_bo_create(gpuvm, obj);
>>>>>> +       if (!vm_bo)
>>>>>> +               return ERR_PTR(-ENOMEM);
>>>>>> +
>>>>>> +       drm_gem_gpuva_assert_lock_held(obj);
>>>>>> +       list_add_tail(&vm_bo->list.entry.gem, &obj-
>>>>>>> gpuva.list);
>>>>>> +
>>>>>> +       return vm_bo;
>>>>>> +}
>>>>>> +EXPORT_SYMBOL_GPL(drm_gpuvm_bo_obtain);
>>>>>> +
>>>>>> +/**
>>>>>> + * drm_gpuvm_bo_obtain_prealloc() - obtains and instance of
>>>>>> the
>>>>>> &drm_gpuvm_bo
>>>>>> + * for the given &drm_gpuvm and &drm_gem_object
>>>>>> + * @__vm_bo: A pre-allocated struct drm_gpuvm_bo.
>>>>>> + *
>>>>>> + * Find the &drm_gpuvm_bo representing the combination of
>>>>>> the
>>>>>> given
>>>>>> + * &drm_gpuvm and &drm_gem_object. If found, increases the
>>>>>> reference
>>>>>> + * count of the found &drm_gpuvm_bo accordingly, while the
>>>>>> @__vm_bo
>>>>>> reference
>>>>>> + * count is decreased. If not found @__vm_bo is returned
>>>>>> without
>>>>>> further
>>>>>> + * increase of the reference count.
>>>>>> + *
>>>>>> + * A new &drm_gpuvm_bo is added to the GEMs gpuva list.
>>>>>> + *
>>>>>> + * Returns: a pointer to the found &drm_gpuvm_bo or @__vm_bo
>>>>>> if
>>>>>> no
>>>>>> existing
>>>>>> + * &drm_gpuvm_bo was found
>>>>>> + */
>>>>>> +struct drm_gpuvm_bo *
>>>>>> +drm_gpuvm_bo_obtain_prealloc(struct drm_gpuvm_bo *__vm_bo)
>>>>>> +{
>>>>>> +       struct drm_gpuvm *gpuvm = __vm_bo->vm;
>>>>>> +       struct drm_gem_object *obj = __vm_bo->obj;
>>>>>> +       struct drm_gpuvm_bo *vm_bo;
>>>>>> +
>>>>>> +       vm_bo = drm_gpuvm_bo_find(gpuvm, obj);
>>>>>> +       if (vm_bo) {
>>>>>> +               drm_gpuvm_bo_put(__vm_bo);
>>>>>> +               return vm_bo;
>>>>>> +       }
>>>>>> +
>>>>>> +       drm_gem_gpuva_assert_lock_held(obj);
>>>>>> +       list_add_tail(&__vm_bo->list.entry.gem, &obj-
>>>>>>> gpuva.list);
>>>>>> +
>>>>>> +       return __vm_bo;
>>>>>> +}
>>>>>> +EXPORT_SYMBOL_GPL(drm_gpuvm_bo_obtain_prealloc);
>>>>>> +
>>>>>>     static int
>>>>>>     __drm_gpuva_insert(struct drm_gpuvm *gpuvm,
>>>>>>                       struct drm_gpuva *va)
>>>>>> @@ -864,24 +1087,33 @@ EXPORT_SYMBOL_GPL(drm_gpuva_remove);
>>>>>>     /**
>>>>>>      * drm_gpuva_link() - link a &drm_gpuva
>>>>>>      * @va: the &drm_gpuva to link
>>>>>> + * @vm_bo: the &drm_gpuvm_bo to add the &drm_gpuva to
>>>>>>      *
>>>>>> - * This adds the given &va to the GPU VA list of the
>>>>>> &drm_gem_object
>>>>>> it is
>>>>>> - * associated with.
>>>>>> + * This adds the given &va to the GPU VA list of the
>>>>>> &drm_gpuvm_bo
>>>>>> and the
>>>>>> + * &drm_gpuvm_bo to the &drm_gem_object it is associated
>>>>>> with.
>>>>>> + *
>>>>>> + * For every &drm_gpuva entry added to the &drm_gpuvm_bo an
>>>>>> additional
>>>>>> + * reference of the latter is taken.
>>>>>>      *
>>>>>>      * This function expects the caller to protect the GEM's
>>>>>> GPUVA
>>>>>> list
>>>>>> against
>>>>>> - * concurrent access using the GEMs dma_resv lock.
>>>>>> + * concurrent access using either the GEMs dma_resv lock or
>>>>>> a
>>>>>> driver
>>>>>> specific
>>>>>> + * lock set through drm_gem_gpuva_set_lock().
>>>>>>      */
>>>>>>     void
>>>>>> -drm_gpuva_link(struct drm_gpuva *va)
>>>>>> +drm_gpuva_link(struct drm_gpuva *va, struct drm_gpuvm_bo
>>>>>> *vm_bo)
>>>>>>     {
>>>>>>            struct drm_gem_object *obj = va->gem.obj;
>>>>>> +       struct drm_gpuvm *gpuvm = va->vm;
>>>>>>     
>>>>>>            if (unlikely(!obj))
>>>>>>                    return;
>>>>>>     
>>>>>> -       drm_gem_gpuva_assert_lock_held(obj);
>>>>>> +       drm_WARN_ON(gpuvm->drm, obj != vm_bo->obj);
>>>>>>     
>>>>>> -       list_add_tail(&va->gem.entry, &obj->gpuva.list);
>>>>>> +       va->vm_bo = drm_gpuvm_bo_get(vm_bo);
>>>>>> +
>>>>>> +       drm_gem_gpuva_assert_lock_held(obj);
>>>>>> +       list_add_tail(&va->gem.entry, &vm_bo->list.gpuva);
>>>>>>     }
>>>>>>     EXPORT_SYMBOL_GPL(drm_gpuva_link);
>>>>>>     
>>>>>> @@ -892,20 +1124,31 @@ EXPORT_SYMBOL_GPL(drm_gpuva_link);
>>>>>>      * This removes the given &va from the GPU VA list of the
>>>>>> &drm_gem_object it is
>>>>>>      * associated with.
>>>>>>      *
>>>>>> + * This removes the given &va from the GPU VA list of the
>>>>>> &drm_gpuvm_bo and
>>>>>> + * the &drm_gpuvm_bo from the &drm_gem_object it is
>>>>>> associated
>>>>>> with
>>>>>> in case
>>>>>> + * this call unlinks the last &drm_gpuva from the
>>>>>> &drm_gpuvm_bo.
>>>>>> + *
>>>>>> + * For every &drm_gpuva entry removed from the &drm_gpuvm_bo
>>>>>> a
>>>>>> reference of
>>>>>> + * the latter is dropped.
>>>>>> + *
>>>>>>      * This function expects the caller to protect the GEM's
>>>>>> GPUVA
>>>>>> list
>>>>>> against
>>>>>> - * concurrent access using the GEMs dma_resv lock.
>>>>>> + * concurrent access using either the GEMs dma_resv lock or
>>>>>> a
>>>>>> driver
>>>>>> specific
>>>>>> + * lock set through drm_gem_gpuva_set_lock().
>>>>>>      */
>>>>>>     void
>>>>>>     drm_gpuva_unlink(struct drm_gpuva *va)
>>>>>>     {
>>>>>>            struct drm_gem_object *obj = va->gem.obj;
>>>>>> +       struct drm_gpuvm_bo *vm_bo = va->vm_bo;
>>>>>>     
>>>>>>            if (unlikely(!obj))
>>>>>>                    return;
>>>>>>     
>>>>>>            drm_gem_gpuva_assert_lock_held(obj);
>>>>>> -
>>>>>>            list_del_init(&va->gem.entry);
>>>>>> +
>>>>>> +       va->vm_bo = NULL;
>>>>>> +       drm_gpuvm_bo_put(vm_bo);
>>>>>>     }
>>>>>>     EXPORT_SYMBOL_GPL(drm_gpuva_unlink);
>>>>>>     
>>>>>> @@ -1050,10 +1293,10 @@ drm_gpuva_remap(struct drm_gpuva
>>>>>> *prev,
>>>>>>                    struct drm_gpuva *next,
>>>>>>                    struct drm_gpuva_op_remap *op)
>>>>>>     {
>>>>>> -       struct drm_gpuva *curr = op->unmap->va;
>>>>>> -       struct drm_gpuvm *gpuvm = curr->vm;
>>>>>> +       struct drm_gpuva *va = op->unmap->va;
>>>>>> +       struct drm_gpuvm *gpuvm = va->vm;
>>>>>>     
>>>>>> -       drm_gpuva_remove(curr);
>>>>>> +       drm_gpuva_remove(va);
>>>>>>     
>>>>>>            if (op->prev) {
>>>>>>                    drm_gpuva_init_from_op(prev, op->prev);
>>>>>> @@ -1695,9 +1938,8 @@ drm_gpuvm_prefetch_ops_create(struct
>>>>>> drm_gpuvm
>>>>>> *gpuvm,
>>>>>>     EXPORT_SYMBOL_GPL(drm_gpuvm_prefetch_ops_create);
>>>>>>     
>>>>>>     /**
>>>>>> - * drm_gpuvm_gem_unmap_ops_create() - creates the
>>>>>> &drm_gpuva_ops
>>>>>> to
>>>>>> unmap a GEM
>>>>>> - * @gpuvm: the &drm_gpuvm representing the GPU VA space
>>>>>> - * @obj: the &drm_gem_object to unmap
>>>>>> + * drm_gpuvm_bo_unmap_ops_create() - creates the
>>>>>> &drm_gpuva_ops
>>>>>> to
>>>>>> unmap a GEM
>>>>>> + * @vm_bo: the &drm_gpuvm_bo abstraction
>>>>>>      *
>>>>>>      * This function creates a list of operations to perform
>>>>>> unmapping
>>>>>> for every
>>>>>>      * GPUVA attached to a GEM.
>>>>>> @@ -1714,15 +1956,14 @@
>>>>>> EXPORT_SYMBOL_GPL(drm_gpuvm_prefetch_ops_create);
>>>>>>      * Returns: a pointer to the &drm_gpuva_ops on success, an
>>>>>> ERR_PTR
>>>>>> on failure
>>>>>>      */
>>>>>>     struct drm_gpuva_ops *
>>>>>> -drm_gpuvm_gem_unmap_ops_create(struct drm_gpuvm *gpuvm,
>>>>>> -                              struct drm_gem_object *obj)
>>>>>> +drm_gpuvm_bo_unmap_ops_create(struct drm_gpuvm_bo *vm_bo)
>>>>>>     {
>>>>>>            struct drm_gpuva_ops *ops;
>>>>>>            struct drm_gpuva_op *op;
>>>>>>            struct drm_gpuva *va;
>>>>>>            int ret;
>>>>>>     
>>>>>> -       drm_gem_gpuva_assert_lock_held(obj);
>>>>>> +       drm_gem_gpuva_assert_lock_held(vm_bo->obj);
>>>>>>     
>>>>>>            ops = kzalloc(sizeof(*ops), GFP_KERNEL);
>>>>>>            if (!ops)
>>>>>> @@ -1730,8 +1971,8 @@ drm_gpuvm_gem_unmap_ops_create(struct
>>>>>> drm_gpuvm
>>>>>> *gpuvm,
>>>>>>     
>>>>>>            INIT_LIST_HEAD(&ops->list);
>>>>>>     
>>>>>> -       drm_gem_for_each_gpuva(va, obj) {
>>>>>> -               op = gpuva_op_alloc(gpuvm);
>>>>>> +       drm_gpuvm_bo_for_each_va(va, vm_bo) {
>>>>>> +               op = gpuva_op_alloc(vm_bo->vm);
>>>>>>                    if (!op) {
>>>>>>                            ret = -ENOMEM;
>>>>>>                            goto err_free_ops;
>>>>>> @@ -1745,10 +1986,10 @@ drm_gpuvm_gem_unmap_ops_create(struct
>>>>>> drm_gpuvm *gpuvm,
>>>>>>            return ops;
>>>>>>     
>>>>>>     err_free_ops:
>>>>>> -       drm_gpuva_ops_free(gpuvm, ops);
>>>>>> +       drm_gpuva_ops_free(vm_bo->vm, ops);
>>>>>>            return ERR_PTR(ret);
>>>>>>     }
>>>>>> -EXPORT_SYMBOL_GPL(drm_gpuvm_gem_unmap_ops_create);
>>>>>> +EXPORT_SYMBOL_GPL(drm_gpuvm_bo_unmap_ops_create);
>>>>>>     
>>>>>>     /**
>>>>>>      * drm_gpuva_ops_free() - free the given &drm_gpuva_ops
>>>>>> diff --git a/drivers/gpu/drm/nouveau/nouveau_uvmm.c
>>>>>> b/drivers/gpu/drm/nouveau/nouveau_uvmm.c
>>>>>> index ed439bf4032f..1e95b0a1b047 100644
>>>>>> --- a/drivers/gpu/drm/nouveau/nouveau_uvmm.c
>>>>>> +++ b/drivers/gpu/drm/nouveau/nouveau_uvmm.c
>>>>>> @@ -62,6 +62,8 @@ struct bind_job_op {
>>>>>>            enum vm_bind_op op;
>>>>>>            u32 flags;
>>>>>>     
>>>>>> +       struct drm_gpuvm_bo *vm_bo;
>>>>>> +
>>>>>>            struct {
>>>>>>                    u64 addr;
>>>>>>                    u64 range;
>>>>>> @@ -1113,22 +1115,28 @@ bind_validate_region(struct
>>>>>> nouveau_job
>>>>>> *job)
>>>>>>     }
>>>>>>     
>>>>>>     static void
>>>>>> -bind_link_gpuvas(struct drm_gpuva_ops *ops, struct
>>>>>> nouveau_uvma_prealloc *new)
>>>>>> +bind_link_gpuvas(struct bind_job_op *bop)
>>>>>>     {
>>>>>> +       struct nouveau_uvma_prealloc *new = &bop->new;
>>>>>> +       struct drm_gpuvm_bo *vm_bo = bop->vm_bo;
>>>>>> +       struct drm_gpuva_ops *ops = bop->ops;
>>>>>>            struct drm_gpuva_op *op;
>>>>>>     
>>>>>>            drm_gpuva_for_each_op(op, ops) {
>>>>>>                    switch (op->op) {
>>>>>>                    case DRM_GPUVA_OP_MAP:
>>>>>> -                       drm_gpuva_link(&new->map->va);
>>>>>> +                       drm_gpuva_link(&new->map->va, vm_bo);
>>>>>>                            break;
>>>>>> -               case DRM_GPUVA_OP_REMAP:
>>>>>> +               case DRM_GPUVA_OP_REMAP: {
>>>>>> +                       struct drm_gpuva *va = op-
>>>>>>> remap.unmap-
>>>>>>> va;
>>>>>> +
>>>>>>                            if (op->remap.prev)
>>>>>> -                               drm_gpuva_link(&new->prev-
>>>>>>> va);
>>>>>> +                               drm_gpuva_link(&new->prev-
>>>>>>> va,
>>>>>> va-
>>>>>>> vm_bo);
>>>>>>                            if (op->remap.next)
>>>>>> -                               drm_gpuva_link(&new->next-
>>>>>>> va);
>>>>>> -                       drm_gpuva_unlink(op->remap.unmap-
>>>>>>> va);
>>>>>> +                               drm_gpuva_link(&new->next-
>>>>>>> va,
>>>>>> va-
>>>>>>> vm_bo);
>>>>>> +                       drm_gpuva_unlink(va);
>>>>>>                            break;
>>>>>> +               }
>>>>>>                    case DRM_GPUVA_OP_UNMAP:
>>>>>>                            drm_gpuva_unlink(op->unmap.va);
>>>>>>                            break;
>>>>>> @@ -1150,10 +1158,18 @@ nouveau_uvmm_bind_job_submit(struct
>>>>>> nouveau_job *job)
>>>>>>     
>>>>>>            list_for_each_op(op, &bind_job->ops) {
>>>>>>                    if (op->op == OP_MAP) {
>>>>>> -                       op->gem.obj =
>>>>>> drm_gem_object_lookup(job-
>>>>>>> file_priv,
>>>>>> -
>>>>>> op-
>>>>>>> gem.handle);
>>>>>> -                       if (!op->gem.obj)
>>>>>> +                       struct drm_gem_object *obj;
>>>>>> +
>>>>>> +                       obj = drm_gem_object_lookup(job-
>>>>>>> file_priv,
>>>>>> +                                                   op-
>>>>>>> gem.handle);
>>>>>> +                       if (!(op->gem.obj = obj))
>>>>>>                                    return -ENOENT;
>>>>>> +
>>>>>> +                       dma_resv_lock(obj->resv, NULL);
>>>>>> +                       op->vm_bo =
>>>>>> drm_gpuvm_bo_obtain(&uvmm-
>>>>>>> base,
>>>>>> obj);
>>>>>> +                       dma_resv_unlock(obj->resv);
>>>>>> +                       if (IS_ERR(op->vm_bo))
>>>>>> +                               return PTR_ERR(op->vm_bo);
>>>>>>                    }
>>>>>>     
>>>>>>                    ret = bind_validate_op(job, op);
>>>>>> @@ -1364,7 +1380,7 @@ nouveau_uvmm_bind_job_submit(struct
>>>>>> nouveau_job
>>>>>> *job)
>>>>>>                    case OP_UNMAP_SPARSE:
>>>>>>                    case OP_MAP:
>>>>>>                    case OP_UNMAP:
>>>>>> -                       bind_link_gpuvas(op->ops, &op->new);
>>>>>> +                       bind_link_gpuvas(op);
>>>>>>                            break;
>>>>>>                    default:
>>>>>>                            break;
>>>>>> @@ -1511,6 +1527,12 @@
>>>>>> nouveau_uvmm_bind_job_free_work_fn(struct
>>>>>> work_struct *work)
>>>>>>                    if (!IS_ERR_OR_NULL(op->ops))
>>>>>>                            drm_gpuva_ops_free(&uvmm->base, op-
>>>>>>> ops);
>>>>>>     
>>>>>> +               if (!IS_ERR_OR_NULL(op->vm_bo)) {
>>>>>> +                       dma_resv_lock(obj->resv, NULL);
>>>>>> +                       drm_gpuvm_bo_put(op->vm_bo);
>>>>>> +                       dma_resv_unlock(obj->resv);
>>>>>> +               }
>>>>>> +
>>>>>>                    if (obj)
>>>>>>                            drm_gem_object_put(obj);
>>>>>>            }
>>>>>> @@ -1776,15 +1798,18 @@ void
>>>>>>     nouveau_uvmm_bo_map_all(struct nouveau_bo *nvbo, struct
>>>>>> nouveau_mem
>>>>>> *mem)
>>>>>>     {
>>>>>>            struct drm_gem_object *obj = &nvbo->bo.base;
>>>>>> +       struct drm_gpuvm_bo *vm_bo;
>>>>>>         ��  struct drm_gpuva *va;
>>>>>>     
>>>>>>            dma_resv_assert_held(obj->resv);
>>>>>>     
>>>>>> -       drm_gem_for_each_gpuva(va, obj) {
>>>>>> -               struct nouveau_uvma *uvma = uvma_from_va(va);
>>>>>> +       drm_gem_for_each_gpuvm_bo(vm_bo, obj) {
>>>>>> +               drm_gpuvm_bo_for_each_va(va, vm_bo) {
>>>>>> +                       struct nouveau_uvma *uvma =
>>>>>> uvma_from_va(va);
>>>>>>     
>>>>>> -               nouveau_uvma_map(uvma, mem);
>>>>>> -               drm_gpuva_invalidate(va, false);
>>>>>> +                       nouveau_uvma_map(uvma, mem);
>>>>>> +                       drm_gpuva_invalidate(va, false);
>>>>>> +               }
>>>>>>            }
>>>>>>     }
>>>>>>     
>>>>>> @@ -1792,15 +1817,18 @@ void
>>>>>>     nouveau_uvmm_bo_unmap_all(struct nouveau_bo *nvbo)
>>>>>>     {
>>>>>>            struct drm_gem_object *obj = &nvbo->bo.base;
>>>>>> +       struct drm_gpuvm_bo *vm_bo;
>>>>>>            struct drm_gpuva *va;
>>>>>>     
>>>>>>            dma_resv_assert_held(obj->resv);
>>>>>>     
>>>>>> -       drm_gem_for_each_gpuva(va, obj) {
>>>>>> -               struct nouveau_uvma *uvma = uvma_from_va(va);
>>>>>> +       drm_gem_for_each_gpuvm_bo(vm_bo, obj) {
>>>>>> +               drm_gpuvm_bo_for_each_va(va, vm_bo) {
>>>>>> +                       struct nouveau_uvma *uvma =
>>>>>> uvma_from_va(va);
>>>>>>     
>>>>>> -         ��     nouveau_uvma_unmap(uvma);
>>>>>> -               drm_gpuva_invalidate(va, true);
>>>>>> +                       nouveau_uvma_unmap(uvma);
>>>>>> +                       drm_gpuva_invalidate(va, true);
>>>>>> +               }
>>>>>>            }
>>>>>>     }
>>>>>>     
>>>>>> diff --git a/include/drm/drm_gem.h b/include/drm/drm_gem.h
>>>>>> index 16364487fde9..369505447acd 100644
>>>>>> --- a/include/drm/drm_gem.h
>>>>>> +++ b/include/drm/drm_gem.h
>>>>>> @@ -580,7 +580,7 @@ int drm_gem_evict(struct drm_gem_object
>>>>>> *obj);
>>>>>>      * drm_gem_gpuva_init() - initialize the gpuva list of a
>>>>>> GEM
>>>>>> object
>>>>>>      * @obj: the &drm_gem_object
>>>>>>      *
>>>>>> - * This initializes the &drm_gem_object's &drm_gpuva list.
>>>>>> + * This initializes the &drm_gem_object's &drm_gpuvm_bo
>>>>>> list.
>>>>>>      *
>>>>>>      * Calling this function is only necessary for drivers
>>>>>> intending to
>>>>>> support the
>>>>>>      * &drm_driver_feature DRIVER_GEM_GPUVA.
>>>>>> @@ -593,28 +593,28 @@ static inline void
>>>>>> drm_gem_gpuva_init(struct
>>>>>> drm_gem_object *obj)
>>>>>>     }
>>>>>>     
>>>>>>     /**
>>>>>> - * drm_gem_for_each_gpuva() - iternator to walk over a list
>>>>>> of
>>>>>> gpuvas
>>>>>> - * @entry__: &drm_gpuva structure to assign to in each
>>>>>> iteration
>>>>>> step
>>>>>> - * @obj__: the &drm_gem_object the &drm_gpuvas to walk are
>>>>>> associated with
>>>>>> + * drm_gem_for_each_gpuvm_bo() - iterator to walk over a
>>>>>> list of
>>>>>> &drm_gpuvm_bo
>>>>>> + * @entry__: &drm_gpuvm_bo structure to assign to in each
>>>>>> iteration
>>>>>> step
>>>>>> + * @obj__: the &drm_gem_object the &drm_gpuvm_bo to walk are
>>>>>> associated with
>>>>>>      *
>>>>>> - * This iterator walks over all &drm_gpuva structures
>>>>>> associated
>>>>>> with the
>>>>>> - * &drm_gpuva_manager.
>>>>>> + * This iterator walks over all &drm_gpuvm_bo structures
>>>>>> associated
>>>>>> with the
>>>>>> + * &drm_gem_object.
>>>>>>      */
>>>>>> -#define drm_gem_for_each_gpuva(entry__, obj__) \
>>>>>> -       list_for_each_entry(entry__, &(obj__)->gpuva.list,
>>>>>> gem.entry)
>>>>>> +#define drm_gem_for_each_gpuvm_bo(entry__, obj__) \
>>>>>> +       list_for_each_entry(entry__, &(obj__)->gpuva.list,
>>>>>> list.entry.gem)
>>>>>>     
>>>>>>     /**
>>>>>> - * drm_gem_for_each_gpuva_safe() - iternator to safely walk
>>>>>> over
>>>>>> a
>>>>>> list of
>>>>>> - * gpuvas
>>>>>> - * @entry__: &drm_gpuva structure to assign to in each
>>>>>> iteration
>>>>>> step
>>>>>> - * @next__: &next &drm_gpuva to store the next step
>>>>>> - * @obj__: the &drm_gem_object the &drm_gpuvas to walk are
>>>>>> associated with
>>>>>> + * drm_gem_for_each_gpuvm_bo_safe() - iterator to safely
>>>>>> walk
>>>>>> over a
>>>>>> list of
>>>>>> + * &drm_gpuvm_bo
>>>>>> + * @entry__: &drm_gpuvm_bostructure to assign to in each
>>>>>> iteration
>>>>>> step
>>>>>> + * @next__: &next &drm_gpuvm_bo to store the next step
>>>>>> + * @obj__: the &drm_gem_object the &drm_gpuvm_bo to walk are
>>>>>> associated with
>>>>>>      *
>>>>>> - * This iterator walks over all &drm_gpuva structures
>>>>>> associated
>>>>>> with the
>>>>>> + * This iterator walks over all &drm_gpuvm_bo structures
>>>>>> associated
>>>>>> with the
>>>>>>      * &drm_gem_object. It is implemented with
>>>>>> list_for_each_entry_safe(), hence
>>>>>>      * it is save against removal of elements.
>>>>>>      */
>>>>>> -#define drm_gem_for_each_gpuva_safe(entry__, next__, obj__)
>>>>>> \
>>>>>> -       list_for_each_entry_safe(entry__, next__, &(obj__)-
>>>>>>> gpuva.list, gem.entry)
>>>>>> +#define drm_gem_for_each_gpuvm_bo_safe(entry__, next__,
>>>>>> obj__) \
>>>>>> +       list_for_each_entry_safe(entry__, next__, &(obj__)-
>>>>>>> gpuva.list, list.entry.gem)
>>>>>>     
>>>>>>     #endif /* __DRM_GEM_H__ */
>>>>>> diff --git a/include/drm/drm_gpuvm.h
>>>>>> b/include/drm/drm_gpuvm.h
>>>>>> index 47cbacb244b9..466fdd76c71a 100644
>>>>>> --- a/include/drm/drm_gpuvm.h
>>>>>> +++ b/include/drm/drm_gpuvm.h
>>>>>> @@ -25,6 +25,7 @@
>>>>>>      * OTHER DEALINGS IN THE SOFTWARE.
>>>>>>      */
>>>>>>     
>>>>>> +#include <linux/dma-resv.h>
>>>>>>     #include <linux/list.h>
>>>>>>     #include <linux/rbtree.h>
>>>>>>     #include <linux/types.h>
>>>>>> @@ -33,6 +34,7 @@
>>>>>>     #include <drm/drm_gem.h>
>>>>>>     
>>>>>>     struct drm_gpuvm;
>>>>>> +struct drm_gpuvm_bo;
>>>>>>     struct drm_gpuvm_ops;
>>>>>>     
>>>>>>     /**
>>>>>> @@ -73,6 +75,12 @@ struct drm_gpuva {
>>>>>>             */
>>>>>>            struct drm_gpuvm *vm;
>>>>>>     
>>>>>> +       /**
>>>>>> +        * @vm_bo: the &drm_gpuvm_bo abstraction for the
>>>>>> mapped
>>>>>> +        * &drm_gem_object
>>>>>> +        */
>>>>>> +       struct drm_gpuvm_bo *vm_bo;
>>>>>> +
>>>>>>            /**
>>>>>>             * @flags: the &drm_gpuva_flags for this mapping
>>>>>>             */
>>>>>> @@ -108,7 +116,7 @@ struct drm_gpuva {
>>>>>>                    struct drm_gem_object *obj;
>>>>>>     
>>>>>>                    /**
>>>>>> -                * @entry: the &list_head to attach this
>>>>>> object
>>>>>> to a
>>>>>> &drm_gem_object
>>>>>> +                * @entry: the &list_head to attach this
>>>>>> object
>>>>>> to a
>>>>>> &drm_gpuvm_bo
>>>>>>                     */
>>>>>>                    struct list_head entry;
>>>>>>            } gem;
>>>>>> @@ -141,7 +149,7 @@ struct drm_gpuva {
>>>>>>     int drm_gpuva_insert(struct drm_gpuvm *gpuvm, struct
>>>>>> drm_gpuva
>>>>>> *va);
>>>>>>     void drm_gpuva_remove(struct drm_gpuva *va);
>>>>>>     
>>>>>> -void drm_gpuva_link(struct drm_gpuva *va);
>>>>>> +void drm_gpuva_link(struct drm_gpuva *va, struct
>>>>>> drm_gpuvm_bo
>>>>>> *vm_bo);
>>>>>>     void drm_gpuva_unlink(struct drm_gpuva *va);
>>>>>>     
>>>>>>     struct drm_gpuva *drm_gpuva_find(struct drm_gpuvm *gpuvm,
>>>>>> @@ -188,10 +196,16 @@ static inline bool
>>>>>> drm_gpuva_invalidated(struct
>>>>>> drm_gpuva *va)
>>>>>>      * enum drm_gpuvm_flags - flags for struct drm_gpuvm
>>>>>>      */
>>>>>>     enum drm_gpuvm_flags {
>>>>>> +       /**
>>>>>> +        * @DRM_GPUVM_RESV_PROTECTED: GPUVM is protected
>>>>>> externally
>>>>>> by the
>>>>>> +        * GPUVM's &dma_resv lock
>>>>>> +        */
>>>>>> +       DRM_GPUVM_RESV_PROTECTED = BIT(0),
>>>>>> +
>>>>>>            /**
>>>>>>             * @DRM_GPUVM_USERBITS: user defined bits
>>>>>>             */
>>>>>> -       DRM_GPUVM_USERBITS = BIT(0),
>>>>>> +       DRM_GPUVM_USERBITS = BIT(1),
>>>>>>     };
>>>>>>     
>>>>>>     /**
>>>>>> @@ -280,6 +294,19 @@ bool drm_gpuvm_interval_empty(struct
>>>>>> drm_gpuvm
>>>>>> *gpuvm, u64 addr, u64 range);
>>>>>>     struct drm_gem_object *
>>>>>>     drm_gpuvm_resv_object_alloc(struct drm_device *drm);
>>>>>>     
>>>>>> +/**
>>>>>> + * drm_gpuvm_resv_protected() - indicates whether
>>>>>> &DRM_GPUVM_RESV_PROTECTED is
>>>>>> + * set
>>>>>> + * @gpuvm: the &drm_gpuvm
>>>>>> + *
>>>>>> + * Returns: true if &DRM_GPUVM_RESV_PROTECTED is set, false
>>>>>> otherwise.
>>>>>> + */
>>>>>> +static inline bool
>>>>>> +drm_gpuvm_resv_protected(struct drm_gpuvm *gpuvm)
>>>>>> +{
>>>>>> +       return gpuvm->flags & DRM_GPUVM_RESV_PROTECTED;
>>>>>> +}
>>>>>> +
>>>>>>     /**
>>>>>>      * drm_gpuvm_resv() - returns the &drm_gpuvm's &dma_resv
>>>>>>      * @gpuvm__: the &drm_gpuvm
>>>>>> @@ -298,6 +325,12 @@ drm_gpuvm_resv_object_alloc(struct
>>>>>> drm_device
>>>>>> *drm);
>>>>>>      */
>>>>>>     #define drm_gpuvm_resv_obj(gpuvm__) ((gpuvm__)->r_obj)
>>>>>>     
>>>>>> +#define drm_gpuvm_resv_held(gpuvm__) \
>>>>>> +       dma_resv_held(drm_gpuvm_resv(gpuvm__))
>>>>>> +
>>>>>> +#define drm_gpuvm_resv_assert_held(gpuvm__) \
>>>>>> +       dma_resv_assert_held(drm_gpuvm_resv(gpuvm__))
>>>>>> +
>>>>>>     #define drm_gpuvm_resv_held(gpuvm__) \
>>>>>>            dma_resv_held(drm_gpuvm_resv(gpuvm__))
>>>>>>     
>>>>>> @@ -382,6 +415,128 @@ __drm_gpuva_next(struct drm_gpuva *va)
>>>>>>     #define drm_gpuvm_for_each_va_safe(va__, next__, gpuvm__)
>>>>>> \
>>>>>>            list_for_each_entry_safe(va__, next__, &(gpuvm__)-
>>>>>>> rb.list,
>>>>>> rb.entry)
>>>>>>     
>>>>>> +/**
>>>>>> + * struct drm_gpuvm_bo - structure representing a &drm_gpuvm
>>>>>> and
>>>>>> + * &drm_gem_object combination
>>>>>> + *
>>>>>> + * This structure is an abstraction representing a
>>>>>> &drm_gpuvm
>>>>>> and
>>>>>> + * &drm_gem_object combination. It serves as an indirection
>>>>>> to
>>>>>> accelerate
>>>>>> + * iterating all &drm_gpuvas within a &drm_gpuvm backed by
>>>>>> the
>>>>>> same
>>>>>> + * &drm_gem_object.
>>>>>> + *
>>>>>> + * Furthermore it is used cache evicted GEM objects for a
>>>>>> certain
>>>>>> GPU-VM to
>>>>>> + * accelerate validation.
>>>>>> + *
>>>>>> + * Typically, drivers want to create an instance of a struct
>>>>>> drm_gpuvm_bo once
>>>>>> + * a GEM object is mapped first in a GPU-VM and release the
>>>>>> instance
>>>>>> once the
>>>>>> + * last mapping of the GEM object in this GPU-VM is
>>>>>> unmapped.
>>>>>> + */
>>>>>> +struct drm_gpuvm_bo {
>>>>>> +       /**
>>>>>> +        * @vm: The &drm_gpuvm the @obj is mapped in. This
>>>>>> pointer is
>>>>>> not
>>>>>> +        * reference counted.
>>>>>> +        *
>>>>>> +        * A struct drm_gpuvm_bo is not allowed to out-live
>>>>>> its
>>>>>> &drm_gpuvm
>>>>>> +        * context. Implicitly, this is ensured by the fact
>>>>>> that
>>>>>> the
>>>>>> driver is
>>>>>> +        * responsible to ensure the VM doesn't contain
>>>>>> mappings
>>>>>> once
>>>>>> it's
>>>>>> +        * freed, since a struct drm_gpuvm_bo should be freed
>>>>>> once
>>>>>> the last
>>>>>> +        * mapping being backed by the corresponding buffer
>>>>>> object is
>>>>>> unmapped.
>>>>>> +        */
>>>>>
>>>>>
>>>>> I don't think the above is completely true. Let's assume in the
>>>>> !RESV_PROTECTED case that a reference is grabbed on the
>>>>> drm_gpuvm_bo
>>>>> during an iteration over a list. Then user-space closes the vm
>>>>> and
>>>>> all
>>>>> vmas are unlinked, but this reference remains but the vm
>>>>> pointer
>>>>> becomes stale. In the RESV_PROTECTED case this is ensured not
>>>>> to
>>>>> happen
>>>>> if by the vm->resv being grabbed during unlink, but in the
>>>>> !RESV_PROTECTED case, the above wording isn't sufficient. The
>>>>> caller
>>>>> needs to ensure the vm stays alive using some sort of similar
>>>>> rule
>>>>> or
>>>>> use kref_get_unless_zero() on the vm under the spinlock if
>>>>> dereferenced.
>>>>
>>>> The list is part of the GPUVM. Hence, the caller *must* either
>>>> already hold
>>>> a reference to the GPUVM or otherwise ensure it's not freed while
>>>> iterating
>>>> this list. All the drm_gpuvm_bo structures within this list can't
>>>> have a
>>>> pointer to another VM than this one by definition.
>>>>
>>>> Anyway, I recognize that this isn't very obvious. Hence, I think
>>>> we
>>>> should
>>>> probably reference count GPUVMs as well. I'd think of the same
>>>> way we
>>>> do it
>>>> with drm_gem_objects. However, I'd prefer to introduce this with
>>>> a
>>>> subsequent
>>>> patch.
>>>
>>> Well, I think we should actually be OK in most cases, and
>>> refcounting
>>> here would probably result in circular dependencies.
>>
>> Where would you see a circular dependency with reference counted
>> GPUVMs?
> 
> It'd be if you call any va_unlink() from the vm destructor. Then the
> destructor will never get called because of the corresponding gpuvm_bo
> vm reference. (IIRC the same argument was made with the vm's resv_bo by
> Christian?)

Well, if that is a use-case it's simply not what the GPUVM's reference
count is intended for. Drivers are free to maintain a driver specific
reference count, counting whatever they want and unlink/remove remaining
stuff this reference counter's callback.

> 
> However if there is a vm_close(), that does all the va_unlink(), that
> will resolve that circular depencency. We do have it in Xe, not sure
> about other drivers.

That's what Nouveau does as well.

> 
> /Thomas
>