Re: [PATCH drm-misc-next v6 3/6] drm/gpuvm: add an abstraction for a VM / BO combination

From: Thomas Hellström
Date: Fri Oct 13 2023 - 08:30:46 EST


On Mon, 2023-10-09 at 01:32 +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@xxxxxxx>
> Signed-off-by: Danilo Krummrich <dakr@xxxxxxxxxx>
> ---
>  drivers/gpu/drm/drm_gpuvm.c            | 332 +++++++++++++++++++++--
> --
>  drivers/gpu/drm/nouveau/nouveau_uvmm.c |  64 +++--
>  include/drm/drm_gem.h                  |  32 +--
>  include/drm/drm_gpuvm.h                | 177 ++++++++++++-
>  4 files changed, 521 insertions(+), 84 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_gpuvm.c
> b/drivers/gpu/drm/drm_gpuvm.c
> index 6368dfdbe9dd..28282283ddaf 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_root_object_alloc().
> + *
> + * In order to connect a struct drm_gpuva its backing
> &drm_gem_object each
NIT: Same as previous patch regarding kerneldoc references

> + * &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;
>   *     }
>   *
> @@ -771,6 +806,194 @@ 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

Kerneldoc uses "Return:" rather than "Returns:", (This seems to a
common thing throughout the series).

> failure
> + */
> +struct drm_gpuvm_bo *

Any particular reason there's line-break after the function type even
when it fits the ~100 char limit?

> +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;
> +
> +       kref_init(&vm_bo->kref);
> +       INIT_LIST_HEAD(&vm_bo->list.gpuva);
> +       INIT_LIST_HEAD(&vm_bo->list.entry.gem);
> +
> +       drm_gem_object_get(obj);

Perhaps group this with the vm_bo->obj assignment to emphasize that
that's the pointer that gets the reference?

> +
> +       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);
> +
> +       drm_gem_gpuva_assert_lock_held(obj);
> +       if (!lock)
> +               drm_gpuvm_resv_assert_held(gpuvm);
> +
> +       list_del(&vm_bo->list.entry.gem);
> +
> +       drm_gem_object_put(obj);

Not sure if we have any drivers utilizing vm_bo_free() yet, but it
might make sense to move the drm_gem_object_put() until after the
freeing below, in case vm_bo_free() wants to use it?

> +
> +       if (ops && ops->vm_bo_free)
> +               ops->vm_bo_free(vm_bo);
> +       else
> +               kfree(vm_bo);
> +}
> +
> +/**
> + * 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);
> +
> +       list_add_tail(&vm_bo->list.entry.gem, &obj->gpuva.list);

Lockdep check?

> +
> +       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;
> +       }
> +
> +       list_add_tail(&__vm_bo->list.entry.gem, &obj->gpuva.list);

Perhaps a lockdep check here?

> +
> +       return __vm_bo;
> +}
> +EXPORT_SYMBOL_GPL(drm_gpuvm_bo_obtain_prealloc);
> +
>  static int
>  __drm_gpuva_insert(struct drm_gpuvm *gpuvm,
>                    struct drm_gpuva *va)
> @@ -860,24 +1083,33 @@ 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

NIT: Referring to a "gem object" as a "GEM" catches my eye every time.
Perhaps that has become common practice? With my "it used to be like.."
hat on, I'd use gem object.

> - * 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;
>  
>         if (unlikely(!obj))
>                 return;
>  
> +       WARN_ON(obj != vm_bo->obj);

Can we use drm_WARN here?

>         drm_gem_gpuva_assert_lock_held(obj);
>  
> -       list_add_tail(&va->gem.entry, &obj->gpuva.list);
> +       drm_gpuvm_bo_get(vm_bo);
> +
> +       va->vm_bo = vm_bo;
> +       list_add_tail(&va->gem.entry, &vm_bo->list.gpuva);
>  }
>  EXPORT_SYMBOL_GPL(drm_gpuva_link);
>  
> @@ -888,13 +1120,22 @@ 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;
> @@ -902,6 +1143,9 @@ drm_gpuva_unlink(struct drm_gpuva *va)
>         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);
>  
> @@ -1046,10 +1290,10 @@ 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);
> @@ -1693,9 +1937,8 @@ 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.
> @@ -1712,15 +1955,14 @@
> 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)
> @@ -1728,8 +1970,8 @@ 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;
> @@ -1743,10 +1985,10 @@ 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 93ad2ba7ec8b..4e46f850e65f 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 13539f32c2e2..ddb0b8d323cf 100644
> --- a/include/drm/drm_gpuvm.h
> +++ b/include/drm/drm_gpuvm.h
> @@ -26,12 +26,14 @@
>   */
>  
>  #include <linux/list.h>
> +#include <linux/dma-resv.h>
>  #include <linux/rbtree.h>
>  #include <linux/types.h>
>  
>  #include <drm/drm_gem.h>
>  
>  struct drm_gpuvm;
> +struct drm_gpuvm_bo;
>  struct drm_gpuvm_ops;
>  
>  /**
> @@ -72,6 +74,12 @@ 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
>          */
> @@ -107,7 +115,7 @@ 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;
> @@ -140,7 +148,7 @@ 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,
> @@ -187,10 +195,16 @@ 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 = (1 << 0),
> +
>         /**
>          * @DRM_GPUVM_USERBITS: user defined bits
>          */
> -       DRM_GPUVM_USERBITS = (1 << 0),
> +       DRM_GPUVM_USERBITS = (1 << 1),
>  };
>  
>  /**
> @@ -272,6 +286,19 @@ bool drm_gpuvm_interval_empty(struct drm_gpuvm
> *gpuvm, u64 addr, u64 range);
>  struct drm_gem_object *
>  drm_gpuvm_root_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
> @@ -290,6 +317,12 @@ drm_gpuvm_root_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__))
>  
> @@ -374,6 +407,117 @@ __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.
Not refcounted. @vm may potentially be freed under us in the
!RESV_PROTECTED case.

> +        */
> +       struct drm_gpuvm *vm;
> +
> +       /**
> +        * @obj: The &drm_gem_object being mapped in @vm.

Refcounted pointer.

> +        */
> +       struct drm_gem_object *obj;
> +
> +       /**
> +        * @kref: The reference count for this &drm_gpuvm_bo.
> +        */
> +       struct kref kref;
> +
> +       /**
> +        * @list: Structure containing all &list_heads.
> +        */
> +       struct {
> +               /**
> +                * @gpuva: The list of linked &drm_gpuvas.
> +                */

Here we should also document how we ensure gpvuas are kept alive.
(which I presume is the lock protecting the gem object's vm_bo list
must be held all the time any gpuva obtained from this list is being
accessed).

> +               struct list_head gpuva;
> +
> +               /**
> +                * @entry: Structure containing all &list_heads
> serving as
> +                * entry.
> +                */
> +               struct {
> +                       /**
> +                        * @gem: List entry to attach to the
> &drm_gem_objects
> +                        * gpuva list.
> +                        */
> +                       struct list_head gem;
> +               } entry;
> +       } list;
> +};
> +
> +struct drm_gpuvm_bo *
> +drm_gpuvm_bo_create(struct drm_gpuvm *gpuvm,
> +                   struct drm_gem_object *obj);
> +
> +struct drm_gpuvm_bo *
> +drm_gpuvm_bo_obtain(struct drm_gpuvm *gpuvm,
> +                   struct drm_gem_object *obj);
> +struct drm_gpuvm_bo *
> +drm_gpuvm_bo_obtain_prealloc(struct drm_gpuvm_bo *vm_bo);
> +
> +/**
> + * drm_gpuvm_bo_get() - acquire a struct drm_gpuvm_bo reference
> + * @vm_bo: the &drm_gpuvm_bo to acquire the reference of
> + *
> + * This function acquires an additional reference to @vm_bo. It is
> illegal to
> + * call this without already holding a reference. No locks required.
> + */
> +static inline struct drm_gpuvm_bo *
> +drm_gpuvm_bo_get(struct drm_gpuvm_bo *vm_bo)
> +{
> +       kref_get(&vm_bo->kref);
> +       return vm_bo;
> +}
> +
> +void drm_gpuvm_bo_put(struct drm_gpuvm_bo *vm_bo);
> +
> +struct drm_gpuvm_bo *
> +drm_gpuvm_bo_find(struct drm_gpuvm *gpuvm,
> +                 struct drm_gem_object *obj);
> +
> +/**
> + * drm_gpuvm_bo_for_each_va() - iterator to walk over a list of
> &drm_gpuva
> + * @va__: &drm_gpuva structure to assign to in each iteration step
> + * @vm_bo__: the &drm_gpuvm_bo the &drm_gpuva to walk are associated
> with
> + *
> + * This iterator walks over all &drm_gpuva structures associated
> with the
> + * &drm_gpuvm_bo.

Must hold the ... lock.


> + */
> +#define drm_gpuvm_bo_for_each_va(va__, vm_bo__) \
> +       list_for_each_entry(va__, &(vm_bo)->list.gpuva, gem.entry)
> +
> +/**
> + * drm_gpuvm_bo_for_each_va_safe() - iterator to safely walk over a
> list of
> + * &drm_gpuva
> + * @va__: &drm_gpuva structure to assign to in each iteration step
> + * @next__: &next &drm_gpuva to store the next step
> + * @vm_bo__: the &drm_gpuvm_bo the &drm_gpuva to walk are associated
> with
> + *
> + * This iterator walks over all &drm_gpuva structures associated
> with the
> + * &drm_gpuvm_bo. It is implemented with list_for_each_entry_safe(),
> hence
> + * it is save against removal of elements.
> + */
> +#define drm_gpuvm_bo_for_each_va_safe(va__, next__, vm_bo__) \
> +       list_for_each_entry_safe(va__, next__, &(vm_bo)->list.gpuva,
> gem.entry)

Same here.

> +
>  /**
>   * enum drm_gpuva_op_type - GPU VA operation type
>   *
> @@ -643,8 +787,7 @@ drm_gpuvm_prefetch_ops_create(struct drm_gpuvm
> *gpuvm,
>                                  u64 addr, u64 range);
>  
>  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);
>  
>  void drm_gpuva_ops_free(struct drm_gpuvm *gpuvm,
>                         struct drm_gpuva_ops *ops);
> @@ -688,6 +831,30 @@ struct drm_gpuvm_ops {
>          */
>         void (*op_free)(struct drm_gpuva_op *op);
>  
> +       /**
> +        * @vm_bo_alloc: called when the &drm_gpuvm allocates
> +        * a struct drm_gpuvm_bo
> +        *
> +        * Some drivers may want to embed struct drm_gpuvm_bo into
> driver
> +        * specific structures. By implementing this callback drivers
> can
> +        * allocate memory accordingly.
> +        *
> +        * This callback is optional.
> +        */
> +       struct drm_gpuvm_bo *(*vm_bo_alloc)(void);
> +
> +       /**
> +        * @vm_bo_free: called when the &drm_gpuvm frees a
> +        * struct drm_gpuvm_bo
> +        *
> +        * Some drivers may want to embed struct drm_gpuvm_bo into
> driver
> +        * specific structures. By implementing this callback drivers
> can
> +        * free the previously allocated memory accordingly.
> +        *
> +        * This callback is optional.
> +        */
> +       void (*vm_bo_free)(struct drm_gpuvm_bo *vm_bo);
> +
>         /**
>          * @sm_step_map: called from &drm_gpuvm_sm_map to finally
> insert the
>          * mapping once all previous steps were completed

Thanks,
Thomas