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Message-ID: <6fa058a4-20d3-44b9-af58-755cfb375d75@redhat.com>
Date:   Tue, 31 Oct 2023 18:38:31 +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>
From:   Danilo Krummrich <dakr@redhat.com>
Organization: RedHat
In-Reply-To: <f00a4975cf32c3ae28124343a2c994acda083829.camel@linux.intel.com>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 8bit
Precedence: bulk

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.

> 
>> +       struct drm_gpuvm *vm;
>> +
>> +       /**
>> +        * @obj: The &drm_gem_object being mapped in @vm. This is a
>> reference
>> +        * counted 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.
>> +                */
>> +               struct list_head gpuva;
> 
> Still missing doc on how the @gpuva stays alive during iteration over
> the list?

Thanks for pointing this out again, I missed that one.

- Danilo

> 
> 
> 
> 8<-------------------------------------------------------------
> 
> Thanks,
> Thomas
>