drm/virtio: Import prime buffers from other devices as guest blobs

By importing scanout buffers from other devices, we should be able
to use the virtio-gpu driver in KMS only mode. Note that we attach
dynamically and register a move_notify() callback so that we can
let the VMM know of any location changes associated with the backing
store of the imported object by sending detach_backing cmd.

Cc: Gerd Hoffmann <kraxel@redhat.com>
Cc: Dmitry Osipenko <dmitry.osipenko@collabora.com>
Cc: Rob Clark <robdclark@gmail.com>
Cc: Gurchetan Singh <gurchetansingh@chromium.org>
Cc: Chia-I Wu <olvaffe@gmail.com>
Signed-off-by: Vivek Kasireddy <vivek.kasireddy@intel.com>
Tested-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
Reviewed-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
[dmitry.osipenko@collabora.com: added kref check to move_notify]
Link: https://patchwork.freedesktop.org/patch/msgid/20241126031643.3490496-5-vivek.kasireddy@intel.com

drivers/gpu/drm/virtio/virtgpu_prime.c

@@ -189,13 +189,18 @@ static void virtgpu_dma_buf_free_obj(struct drm_gem_object *obj)
 	struct virtio_gpu_object *bo = gem_to_virtio_gpu_obj(obj);
 	struct virtio_gpu_device *vgdev = obj->dev->dev_private;
 	struct dma_buf_attachment *attach = obj->import_attach;
+	struct dma_resv *resv = attach->dmabuf->resv;
 
 	if (attach) {
+		dma_resv_lock(resv, NULL);
+
 		virtio_gpu_detach_object_fenced(bo);
 
 		if (bo->sgt)
-			dma_buf_unmap_attachment_unlocked(attach, bo->sgt,
-							  DMA_BIDIRECTIONAL);
+			dma_buf_unmap_attachment(attach, bo->sgt,
+						 DMA_BIDIRECTIONAL);
+
+		dma_resv_unlock(resv);
 
 		dma_buf_detach(attach->dmabuf, attach);
 		dma_buf_put(attach->dmabuf);
@@ -259,10 +264,39 @@ static int virtgpu_dma_buf_init_obj(struct drm_device *dev,
 	return ret;
 }
 
+static const struct drm_gem_object_funcs virtgpu_gem_dma_buf_funcs = {
+	.free = virtgpu_dma_buf_free_obj,
+};
+
+static void virtgpu_dma_buf_move_notify(struct dma_buf_attachment *attach)
+{
+	struct drm_gem_object *obj = attach->importer_priv;
+	struct virtio_gpu_object *bo = gem_to_virtio_gpu_obj(obj);
+
+	if (bo->created && kref_read(&obj->refcount)) {
+		virtio_gpu_detach_object_fenced(bo);
+
+		if (bo->sgt)
+			dma_buf_unmap_attachment(attach, bo->sgt,
+						 DMA_BIDIRECTIONAL);
+
+		bo->sgt = NULL;
+	}
+}
+
+static const struct dma_buf_attach_ops virtgpu_dma_buf_attach_ops = {
+	.allow_peer2peer = true,
+	.move_notify = virtgpu_dma_buf_move_notify
+};
+
 struct drm_gem_object *virtgpu_gem_prime_import(struct drm_device *dev,
 						struct dma_buf *buf)
 {
+	struct virtio_gpu_device *vgdev = dev->dev_private;
+	struct dma_buf_attachment *attach;
+	struct virtio_gpu_object *bo;
 	struct drm_gem_object *obj;
+	int ret;
 
 	if (buf->ops == &virtgpu_dmabuf_ops.ops) {
 		obj = buf->priv;
@@ -276,7 +310,32 @@ struct drm_gem_object *virtgpu_gem_prime_import(struct drm_device *dev,
 		}
 	}
 
-	return drm_gem_prime_import(dev, buf);
+	if (!vgdev->has_resource_blob || vgdev->has_virgl_3d)
+		return drm_gem_prime_import(dev, buf);
+
+	bo = kzalloc(sizeof(*bo), GFP_KERNEL);
+	if (!bo)
+		return ERR_PTR(-ENOMEM);
+
+	obj = &bo->base.base;
+	obj->funcs = &virtgpu_gem_dma_buf_funcs;
+	drm_gem_private_object_init(dev, obj, buf->size);
+
+	attach = dma_buf_dynamic_attach(buf, dev->dev,
+					&virtgpu_dma_buf_attach_ops, obj);
+	if (IS_ERR(attach)) {
+		kfree(bo);
+		return ERR_CAST(attach);
+	}
+
+	obj->import_attach = attach;
+	get_dma_buf(buf);
+
+	ret = virtgpu_dma_buf_init_obj(dev, bo, attach);
+	if (ret < 0)
+		return ERR_PTR(ret);
+
+	return obj;
 }
 
 struct drm_gem_object *virtgpu_gem_prime_import_sg_table(