drm/gpuvm: reference count drm_gpuvm structures

Implement reference counting for struct drm_gpuvm.
Acked-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
Signed-off-by: Danilo Krummrich <dakr@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20231108001259.15123-10-dakr@redhat.com

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 +785,35 @@ 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);
+
+	drm_gpuvm_fini(gpuvm);
+
+	if (drm_WARN_ON(gpuvm->drm, !gpuvm->ops->vm_free))
+		return;
+
+	gpuvm->ops->vm_free(gpuvm);
+}
+
+/**
+ * drm_gpuvm_put() - drop a struct drm_gpuvm reference
+ * @gpuvm: the &drm_gpuvm to release the reference of
+ *
+ * This releases a reference to @gpuvm.
+ *
+ * This function may be called from atomic context.
+ */
+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,
@@ -839,11 +862,21 @@ drm_gpuva_insert(struct drm_gpuvm *gpuvm,
 {
 	u64 addr = va->va.addr;
 	u64 range = va->va.range;
+	int ret;
 
 	if (unlikely(!drm_gpuvm_range_valid(gpuvm, addr, range)))
 		return -EINVAL;
 
-	return __drm_gpuva_insert(gpuvm, va);
+	ret = __drm_gpuva_insert(gpuvm, va);
+	if (likely(!ret))
+		/* Take a reference of the GPUVM for the successfully inserted
+		 * drm_gpuva. We can't take the reference in
+		 * __drm_gpuva_insert() itself, since we don't want to increse
+		 * the reference count for the GPUVM's kernel_alloc_node.
+		 */
+		drm_gpuvm_get(gpuvm);
+
+	return ret;
 }
 EXPORT_SYMBOL_GPL(drm_gpuva_insert);
 
@@ -876,6 +909,7 @@ drm_gpuva_remove(struct drm_gpuva *va)
 	}
 
 	__drm_gpuva_remove(va);
+	drm_gpuvm_put(va->vm);
 }
 EXPORT_SYMBOL_GPL(drm_gpuva_remove);
 

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);
 }

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