Re: [PATCH drm-misc-next v6 1/6] drm/gpuvm: add common dma-resv per struct drm_gpuvm

[Thomas Hellström]

On Mon, 2023-10-09 at 01:32 +0200, Danilo Krummrich wrote:
> Provide a common dma-resv for GEM objects not being used outside of
> this
> GPU-VM. This is used in a subsequent patch to generalize dma-resv,
> external and evicted object handling and GEM validation.
> 
> Signed-off-by: Danilo Krummrich <dakr@xxxxxxxxxx>
> ---
>  drivers/gpu/drm/drm_gpuvm.c            | 56
> +++++++++++++++++++++++++-
>  drivers/gpu/drm/nouveau/nouveau_uvmm.c | 13 +++++-
>  include/drm/drm_gpuvm.h                | 35 +++++++++++++++-
>  3 files changed, 99 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_gpuvm.c
> b/drivers/gpu/drm/drm_gpuvm.c
> index 02ecb45a2544..ebda9d594165 100644
> --- a/drivers/gpu/drm/drm_gpuvm.c
> +++ b/drivers/gpu/drm/drm_gpuvm.c
> @@ -61,6 +61,15 @@
>   * contained within struct drm_gpuva already. Hence, for inserting
> &drm_gpuva
>   * entries from within dma-fence signalling critical sections it is
> enough to
>   * pre-allocate the &drm_gpuva structures.
> + *
> + * &drm_gem_objects which are private to a single VM can share a
> common
> + * &dma_resv in order to improve locking efficiency (e.g. with
> &drm_exec).
> + * For this purpose drivers must pass a &drm_gem_object to
> drm_gpuvm_init(), in
> + * the following called 'root object', which serves as the container

Nit: Perhaps resv object altough it might typically be the root page-
table object, that doesn't have any meaning to drm_gpuvm, which uses it
solely as a container for the resv?

> of the
> + * GPUVM's shared &dma_resv. This root object can be a driver
> specific
> + * &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().
>   */
>  
>  /**
> @@ -652,9 +661,47 @@ drm_gpuvm_range_valid(struct drm_gpuvm *gpuvm,
>                !drm_gpuvm_in_kernel_node(gpuvm, addr, range);
>  }
>  
> +static void
> +drm_gpuvm_gem_object_free(struct drm_gem_object *obj)
> +{
> +       drm_gem_object_release(obj);
> +       kfree(obj);
> +}
> +
> +static const struct drm_gem_object_funcs drm_gpuvm_object_funcs = {
> +       .free = drm_gpuvm_gem_object_free,
> +};
> +
> +/**
> + * drm_gpuvm_root_object_alloc() - allocate a dummy &drm_gem_object
> + * @drm: the drivers &drm_device
> + *
> + * Allocates a dummy &drm_gem_object which can be passed to
> drm_gpuvm_init() in
> + * order to serve as root GEM object providing the &drm_resv shared
> across
> + * &drm_gem_objects local to a single GPUVM.
> + *
> + * Returns: the &drm_gem_object on success, NULL on failure
> + */
> +struct drm_gem_object *
> +drm_gpuvm_root_object_alloc(struct drm_device *drm)
> +{
> +       struct drm_gem_object *obj;
> +
> +       obj = kzalloc(sizeof(*obj), GFP_KERNEL);
> +       if (!obj)
> +               return NULL;
> +
> +       obj->funcs = &drm_gpuvm_object_funcs;
> +       drm_gem_private_object_init(drm, obj, 0);
> +
> +       return obj;
> +}
> +EXPORT_SYMBOL_GPL(drm_gpuvm_root_object_alloc);
> +
>  /**
>   * drm_gpuvm_init() - initialize a &drm_gpuvm
>   * @gpuvm: pointer to the &drm_gpuvm to initialize
> + * @r_obj: the root &drm_gem_object providing the GPUVM's common
> &dma_resv
>   * @name: the name of the GPU VA space
>   * @start_offset: the start offset of the GPU VA space
>   * @range: the size of the GPU VA space
> @@ -668,7 +715,7 @@ drm_gpuvm_range_valid(struct drm_gpuvm *gpuvm,
>   * &name is expected to be managed by the surrounding driver
> structures.
>   */
>  void
> -drm_gpuvm_init(struct drm_gpuvm *gpuvm,
> +drm_gpuvm_init(struct drm_gpuvm *gpuvm, struct drm_gem_object
> *r_obj,
>                const char *name,
>                u64 start_offset, u64 range,
>                u64 reserve_offset, u64 reserve_range,
> @@ -683,6 +730,9 @@ drm_gpuvm_init(struct drm_gpuvm *gpuvm,
>  
>         gpuvm->name = name ? name : "unknown";
>         gpuvm->ops = ops;
> +       gpuvm->r_obj = r_obj;
> +
> +       drm_gem_object_get(r_obj);
>  
>         memset(&gpuvm->kernel_alloc_node, 0, sizeof(struct
> drm_gpuva));
>  
> @@ -713,7 +763,9 @@ drm_gpuvm_destroy(struct drm_gpuvm *gpuvm)
>                 __drm_gpuva_remove(&gpuvm->kernel_alloc_node);
>  
>         WARN(!RB_EMPTY_ROOT(&gpuvm->rb.tree.rb_root),
> -            "GPUVA tree is not empty, potentially leaking memory.");
> +            "GPUVA tree is not empty, potentially leaking
> memory.\n");

Should we cache the drm device in struct drm_gpuvm and use drm_warn()
here instead of WARN?

> +
> +       drm_gem_object_put(gpuvm->r_obj);
>  }
>  EXPORT_SYMBOL_GPL(drm_gpuvm_destroy);
>  
> diff --git a/drivers/gpu/drm/nouveau/nouveau_uvmm.c
> b/drivers/gpu/drm/nouveau/nouveau_uvmm.c
> index 5cf892c50f43..4dea847ef989 100644
> --- a/drivers/gpu/drm/nouveau/nouveau_uvmm.c
> +++ b/drivers/gpu/drm/nouveau/nouveau_uvmm.c
> @@ -1808,8 +1808,9 @@ int
>  nouveau_uvmm_init(struct nouveau_uvmm *uvmm, struct nouveau_cli
> *cli,
>                   u64 kernel_managed_addr, u64 kernel_managed_size)
>  {
> -       int ret;
> +       struct drm_gem_object *r_obj;
>         u64 kernel_managed_end = kernel_managed_addr +
> kernel_managed_size;
> +       int ret;
>  
>         mutex_init(&uvmm->mutex);
>         dma_resv_init(&uvmm->resv);
> @@ -1833,14 +1834,22 @@ nouveau_uvmm_init(struct nouveau_uvmm *uvmm,
> struct nouveau_cli *cli,
>                 goto out_unlock;
>         }
>  
> +       r_obj = drm_gpuvm_root_object_alloc(cli->drm->dev);
> +       if (!r_obj) {
> +               ret = -ENOMEM;
> +               goto out_unlock;
> +       }
> +
>         uvmm->kernel_managed_addr = kernel_managed_addr;
>         uvmm->kernel_managed_size = kernel_managed_size;
>  
> -       drm_gpuvm_init(&uvmm->base, cli->name,
> +       drm_gpuvm_init(&uvmm->base, r_obj, cli->name,
>                        NOUVEAU_VA_SPACE_START,
>                        NOUVEAU_VA_SPACE_END,
>                        kernel_managed_addr, kernel_managed_size,
>                        NULL);
> +       /* GPUVM takes care from here on. */
> +       drm_gem_object_put(r_obj);
>  
>         ret = nvif_vmm_ctor(&cli->mmu, "uvmm",
>                             cli->vmm.vmm.object.oclass, RAW,
> diff --git a/include/drm/drm_gpuvm.h b/include/drm/drm_gpuvm.h
> index c7ed6bf441d4..0aec14d8b259 100644
> --- a/include/drm/drm_gpuvm.h
> +++ b/include/drm/drm_gpuvm.h
> @@ -238,9 +238,15 @@ struct drm_gpuvm {
>          * @ops: &drm_gpuvm_ops providing the split/merge steps to
> drivers
>          */
>         const struct drm_gpuvm_ops *ops;
> +
> +       /**
> +        * @r_obj: Root GEM object; representing the GPUVM's common
> &dma_resv.
> +        */
> +       struct drm_gem_object *r_obj;
>  };
>  
> -void drm_gpuvm_init(struct drm_gpuvm *gpuvm, const char *name,
> +void drm_gpuvm_init(struct drm_gpuvm *gpuvm, struct drm_gem_object
> *r_obj,
> +                   const char *name,
>                     u64 start_offset, u64 range,
>                     u64 reserve_offset, u64 reserve_range,
>                     const struct drm_gpuvm_ops *ops);
> @@ -248,6 +254,33 @@ void drm_gpuvm_destroy(struct drm_gpuvm *gpuvm);
>  
>  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() - returns the &drm_gpuvm's &dma_resv
> + * @gpuvm__: the &drm_gpuvm
> + *
> + * Returns: a pointer to the &drm_gpuvm's shared &dma_resv
> + */
> +#define drm_gpuvm_resv(gpuvm__) ((gpuvm__)->r_obj->resv)
> +
> +/**
> + * drm_gpuvm_resv_obj() - returns the &drm_gem_object holding the
> &drm_gpuvm's
> + * &dma_resv
> + * @gpuvm__: the &drm_gpuvm
> + *
> + * Returns: a pointer to the &drm_gem_object holding the
> &drm_gpuvm's shared
> + * &dma_resv
> + */
> +#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__))
> +
>  static inline struct drm_gpuva *
>  __drm_gpuva_next(struct drm_gpuva *va)
>  {

Reviewed-by: Thomas Hellström <thomas.hellstrom@xxxxxxxxxxxxxxx>