Re: [PATCH drm-misc-next v8 09/12] drm/gpuvm: reference count drm_gpuvm structures

["Thomas Hellström" <thomas.hellstrom@linux.intel.com>]

On Thu, 2023-11-02 at 00:31 +0100, Danilo Krummrich wrote:
> Implement reference counting for struct drm_gpuvm.
> 
> Signed-off-by: Danilo Krummrich <dakr@redhat.com>

Will port the Xe series over to check that it works properly and get
back with review on this one.


> ---
>  drivers/gpu/drm/drm_gpuvm.c            | 44 +++++++++++++++++++-----
> --
>  drivers/gpu/drm/nouveau/nouveau_uvmm.c | 20 +++++++++---
>  include/drm/drm_gpuvm.h                | 31 +++++++++++++++++-
>  3 files changed, 78 insertions(+), 17 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_gpuvm.c
> b/drivers/gpu/drm/drm_gpuvm.c
> index 53e2c406fb04..6a88eafc5229 100644
> --- a/drivers/gpu/drm/drm_gpuvm.c
> +++ b/drivers/gpu/drm/drm_gpuvm.c
> @@ -746,6 +746,8 @@ drm_gpuvm_init(struct drm_gpuvm *gpuvm, const
> char *name,
>         gpuvm->rb.tree = RB_ROOT_CACHED;
>         INIT_LIST_HEAD(&gpuvm->rb.list);
>  
> +       kref_init(&gpuvm->kref);
> +
>         gpuvm->name = name ? name : "unknown";
>         gpuvm->flags = flags;
>         gpuvm->ops = ops;
> @@ -770,15 +772,8 @@ drm_gpuvm_init(struct drm_gpuvm *gpuvm, const
> char *name,
>  }
>  EXPORT_SYMBOL_GPL(drm_gpuvm_init);
>  
> -/**
> - * drm_gpuvm_destroy() - cleanup a &drm_gpuvm
> - * @gpuvm: pointer to the &drm_gpuvm to clean up
> - *
> - * Note that it is a bug to call this function on a manager that
> still
> - * holds GPU VA mappings.
> - */
> -void
> -drm_gpuvm_destroy(struct drm_gpuvm *gpuvm)
> +static void
> +drm_gpuvm_fini(struct drm_gpuvm *gpuvm)
>  {
>         gpuvm->name = NULL;
>  
> @@ -790,7 +785,33 @@ drm_gpuvm_destroy(struct drm_gpuvm *gpuvm)
>  
>         drm_gem_object_put(gpuvm->r_obj);
>  }
> -EXPORT_SYMBOL_GPL(drm_gpuvm_destroy);
> +
> +static void
> +drm_gpuvm_free(struct kref *kref)
> +{
> +       struct drm_gpuvm *gpuvm = container_of(kref, struct
> drm_gpuvm, kref);
> +
> +       if (drm_WARN_ON(gpuvm->drm, !gpuvm->ops->vm_free))
> +               return;
> +
> +       drm_gpuvm_fini(gpuvm);
> +
> +       gpuvm->ops->vm_free(gpuvm);
> +}
> +
> +/**
> + * drm_gpuvm_bo_put() - drop a struct drm_gpuvm reference
> + * @gpuvm: the &drm_gpuvm to release the reference of
> + *
> + * This releases a reference to @gpuvm.
> + */
> +void
> +drm_gpuvm_put(struct drm_gpuvm *gpuvm)
> +{
> +       if (gpuvm)
> +               kref_put(&gpuvm->kref, drm_gpuvm_free);
> +}
> +EXPORT_SYMBOL_GPL(drm_gpuvm_put);
>  
>  static int
>  __drm_gpuva_insert(struct drm_gpuvm *gpuvm,
> @@ -843,7 +864,7 @@ drm_gpuva_insert(struct drm_gpuvm *gpuvm,
>         if (unlikely(!drm_gpuvm_range_valid(gpuvm, addr, range)))
>                 return -EINVAL;
>  
> -       return __drm_gpuva_insert(gpuvm, va);
> +       return __drm_gpuva_insert(drm_gpuvm_get(gpuvm), va);
>  }
>  EXPORT_SYMBOL_GPL(drm_gpuva_insert);
>  
> @@ -876,6 +897,7 @@ drm_gpuva_remove(struct drm_gpuva *va)
>         }
>  
>         __drm_gpuva_remove(va);
> +       drm_gpuvm_put(va->vm);
>  }
>  EXPORT_SYMBOL_GPL(drm_gpuva_remove);
>  
> diff --git a/drivers/gpu/drm/nouveau/nouveau_uvmm.c
> b/drivers/gpu/drm/nouveau/nouveau_uvmm.c
> index 54be12c1272f..cb2f06565c46 100644
> --- a/drivers/gpu/drm/nouveau/nouveau_uvmm.c
> +++ b/drivers/gpu/drm/nouveau/nouveau_uvmm.c
> @@ -1780,6 +1780,18 @@ nouveau_uvmm_bo_unmap_all(struct nouveau_bo
> *nvbo)
>         }
>  }
>  
> +static void
> +nouveau_uvmm_free(struct drm_gpuvm *gpuvm)
> +{
> +       struct nouveau_uvmm *uvmm = uvmm_from_gpuvm(gpuvm);
> +
> +       kfree(uvmm);
> +}
> +
> +static const struct drm_gpuvm_ops gpuvm_ops = {
> +       .vm_free = nouveau_uvmm_free,
> +};
> +
>  int
>  nouveau_uvmm_ioctl_vm_init(struct drm_device *dev,
>                            void *data,
> @@ -1830,7 +1842,7 @@ nouveau_uvmm_ioctl_vm_init(struct drm_device
> *dev,
>                        NOUVEAU_VA_SPACE_END,
>                        init->kernel_managed_addr,
>                        init->kernel_managed_size,
> -                      NULL);
> +                      &gpuvm_ops);
>         /* GPUVM takes care from here on. */
>         drm_gem_object_put(r_obj);
>  
> @@ -1849,8 +1861,7 @@ nouveau_uvmm_ioctl_vm_init(struct drm_device
> *dev,
>         return 0;
>  
>  out_gpuvm_fini:
> -       drm_gpuvm_destroy(&uvmm->base);
> -       kfree(uvmm);
> +       drm_gpuvm_put(&uvmm->base);
>  out_unlock:
>         mutex_unlock(&cli->mutex);
>         return ret;
> @@ -1902,7 +1913,6 @@ nouveau_uvmm_fini(struct nouveau_uvmm *uvmm)
>  
>         mutex_lock(&cli->mutex);
>         nouveau_vmm_fini(&uvmm->vmm);
> -       drm_gpuvm_destroy(&uvmm->base);
> -       kfree(uvmm);
> +       drm_gpuvm_put(&uvmm->base);
>         mutex_unlock(&cli->mutex);
>  }
> diff --git a/include/drm/drm_gpuvm.h b/include/drm/drm_gpuvm.h
> index 0c2e24155a93..4e6e1fd3485a 100644
> --- a/include/drm/drm_gpuvm.h
> +++ b/include/drm/drm_gpuvm.h
> @@ -247,6 +247,11 @@ struct drm_gpuvm {
>                 struct list_head list;
>         } rb;
>  
> +       /**
> +        * @kref: reference count of this object
> +        */
> +       struct kref kref;
> +
>         /**
>          * @kernel_alloc_node:
>          *
> @@ -273,7 +278,23 @@ void drm_gpuvm_init(struct drm_gpuvm *gpuvm,
> const char *name,
>                     u64 start_offset, u64 range,
>                     u64 reserve_offset, u64 reserve_range,
>                     const struct drm_gpuvm_ops *ops);
> -void drm_gpuvm_destroy(struct drm_gpuvm *gpuvm);
> +
> +/**
> + * drm_gpuvm_get() - acquire a struct drm_gpuvm reference
> + * @gpuvm: the &drm_gpuvm to acquire the reference of
> + *
> + * This function acquires an additional reference to @gpuvm. It is
> illegal to
> + * call this without already holding a reference. No locks required.
> + */
> +static inline struct drm_gpuvm *
> +drm_gpuvm_get(struct drm_gpuvm *gpuvm)
> +{
> +       kref_get(&gpuvm->kref);
> +
> +       return gpuvm;
> +}
> +
> +void drm_gpuvm_put(struct drm_gpuvm *gpuvm);
>  
>  bool drm_gpuvm_range_valid(struct drm_gpuvm *gpuvm, u64 addr, u64
> range);
>  bool drm_gpuvm_interval_empty(struct drm_gpuvm *gpuvm, u64 addr, u64
> range);
> @@ -673,6 +694,14 @@ static inline void drm_gpuva_init_from_op(struct
> drm_gpuva *va,
>   * operations to drivers.
>   */
>  struct drm_gpuvm_ops {
> +       /**
> +        * @vm_free: called when the last reference of a struct
> drm_gpuvm is
> +        * dropped
> +        *
> +        * This callback is mandatory.
> +        */
> +       void (*vm_free)(struct drm_gpuvm *gpuvm);
> +
>         /**
>          * @op_alloc: called when the &drm_gpuvm allocates
>          * a struct drm_gpuva_op