drm/gpuvm: add common dma-resv per struct drm_gpuvm

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.
Acked-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
Reviewed-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Signed-off-by: Danilo Krummrich <dakr@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20231108001259.15123-6-dakr@redhat.com

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 'resv object', which serves as the container of the
+ * GPUVM's shared &dma_resv. This resv 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_resv_object_alloc().
  */
 
 /**
@@ -670,11 +679,49 @@ drm_gpuvm_range_valid(struct drm_gpuvm *gpuvm,
 }
 EXPORT_SYMBOL_GPL(drm_gpuvm_range_valid);
 
+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_resv_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_resv_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_resv_object_alloc);
+
 /**
  * drm_gpuvm_init() - initialize a &drm_gpuvm
  * @gpuvm: pointer to the &drm_gpuvm to initialize
  * @name: the name of the GPU VA space
  * @drm: the &drm_device this VM resides in
+ * @r_obj: the resv &drm_gem_object providing the GPUVM's common &dma_resv
  * @start_offset: the start offset of the GPU VA space
  * @range: the size of the GPU VA space
  * @reserve_offset: the start of the kernel reserved GPU VA area
@@ -689,6 +736,7 @@ EXPORT_SYMBOL_GPL(drm_gpuvm_range_valid);
 void
 drm_gpuvm_init(struct drm_gpuvm *gpuvm, const char *name,
 	       struct drm_device *drm,
+	       struct drm_gem_object *r_obj,
 	       u64 start_offset, u64 range,
 	       u64 reserve_offset, u64 reserve_range,
 	       const struct drm_gpuvm_ops *ops)
@@ -699,6 +747,9 @@ drm_gpuvm_init(struct drm_gpuvm *gpuvm, const char *name,
 	gpuvm->name = name ? name : "unknown";
 	gpuvm->ops = ops;
 	gpuvm->drm = drm;
+	gpuvm->r_obj = r_obj;
+
+	drm_gem_object_get(r_obj);
 
 	drm_gpuvm_warn_check_overflow(gpuvm, start_offset, range);
 	gpuvm->mm_start = start_offset;
@@ -733,6 +784,8 @@ drm_gpuvm_destroy(struct drm_gpuvm *gpuvm)
 
 	drm_WARN(gpuvm->drm, !RB_EMPTY_ROOT(&gpuvm->rb.tree.rb_root),
 		 "GPUVA tree is not empty, potentially leaking memory.\n");
+
+	drm_gem_object_put(gpuvm->r_obj);
 }
 EXPORT_SYMBOL_GPL(drm_gpuvm_destroy);
 

drivers/gpu/drm/nouveau/nouveau_uvmm.c

@@ -1797,8 +1797,9 @@ nouveau_uvmm_init(struct nouveau_uvmm *uvmm, struct nouveau_cli *cli,
 		  u64 kernel_managed_addr, u64 kernel_managed_size)
 {
 	struct drm_device *drm = cli->drm->dev;
-	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);
@@ -1822,11 +1823,19 @@ nouveau_uvmm_init(struct nouveau_uvmm *uvmm, struct nouveau_cli *cli,
 		goto out_unlock;
 	}
 
-	drm_gpuvm_init(&uvmm->base, cli->name, drm,
+	r_obj = drm_gpuvm_resv_object_alloc(drm);
+	if (!r_obj) {
+		ret = -ENOMEM;
+		goto out_unlock;
+	}
+
+	drm_gpuvm_init(&uvmm->base, cli->name, drm, r_obj,
 		       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,

include/drm/drm_gpuvm.h

@@ -244,10 +244,16 @@ struct drm_gpuvm {
 	 * @ops: &drm_gpuvm_ops providing the split/merge steps to drivers
 	 */
 	const struct drm_gpuvm_ops *ops;
+
+	/**
+	 * @r_obj: Resv 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,
 		    struct drm_device *drm,
+		    struct drm_gem_object *r_obj,
 		    u64 start_offset, u64 range,
 		    u64 reserve_offset, u64 reserve_range,
 		    const struct drm_gpuvm_ops *ops);
@@ -256,6 +262,33 @@ void drm_gpuvm_destroy(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);
 
+struct drm_gem_object *
+drm_gpuvm_resv_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)
 {