drm/msm/gem: Add metadata

The EXT_external_objects extension is a bit awkward as it doesn't pass
explicit modifiers, leaving the importer to guess with incomplete
information.  In the case of vk (turnip) exporting and gl (freedreno)
importing, the "OPTIMAL_TILING_EXT" layout depends on VkImageCreateInfo
flags (among other things), which the importer does not know.  Which
unfortunately leaves us with the need for a metadata back-channel.

The contents of the metadata are defined by userspace.  The
EXT_external_objects extension is only required to work between
compatible versions of gl and vk drivers, as defined by device and
driver UUIDs.

v2: add missing metadata kfree
v3: Rework to move copy_from/to_user out from under gem obj lock
    to avoid angering lockdep about deadlocks against fs-reclaim

Signed-off-by: Rob Clark <robdclark@chromium.org>
Patchwork: https://patchwork.freedesktop.org/patch/566157/

drivers/gpu/drm/msm/msm_drv.c

@@ -37,9 +37,10 @@
  * - 1.9.0 - Add MSM_SUBMIT_FENCE_SN_IN
  * - 1.10.0 - Add MSM_SUBMIT_BO_NO_IMPLICIT
  * - 1.11.0 - Add wait boost (MSM_WAIT_FENCE_BOOST, MSM_PREP_BOOST)
+ * - 1.12.0 - Add MSM_INFO_SET_METADATA and MSM_INFO_GET_METADATA
  */
 #define MSM_VERSION_MAJOR	1
-#define MSM_VERSION_MINOR	11
+#define MSM_VERSION_MINOR	12
 #define MSM_VERSION_PATCHLEVEL	0
 
 static void msm_deinit_vram(struct drm_device *ddev);
@@ -546,6 +547,85 @@ static int msm_ioctl_gem_info_set_iova(struct drm_device *dev,
 	return msm_gem_set_iova(obj, ctx->aspace, iova);
 }
 
+static int msm_ioctl_gem_info_set_metadata(struct drm_gem_object *obj,
+					   __user void *metadata,
+					   u32 metadata_size)
+{
+	struct msm_gem_object *msm_obj = to_msm_bo(obj);
+	void *buf;
+	int ret;
+
+	/* Impose a moderate upper bound on metadata size: */
+	if (metadata_size > 128) {
+		return -EOVERFLOW;
+	}
+
+	/* Use a temporary buf to keep copy_from_user() outside of gem obj lock: */
+	buf = memdup_user(metadata, metadata_size);
+	if (IS_ERR(buf))
+		return PTR_ERR(buf);
+
+	ret = msm_gem_lock_interruptible(obj);
+	if (ret)
+		goto out;
+
+	msm_obj->metadata =
+		krealloc(msm_obj->metadata, metadata_size, GFP_KERNEL);
+	msm_obj->metadata_size = metadata_size;
+	memcpy(msm_obj->metadata, buf, metadata_size);
+
+	msm_gem_unlock(obj);
+
+out:
+	kfree(buf);
+
+	return ret;
+}
+
+static int msm_ioctl_gem_info_get_metadata(struct drm_gem_object *obj,
+					   __user void *metadata,
+					   u32 *metadata_size)
+{
+	struct msm_gem_object *msm_obj = to_msm_bo(obj);
+	void *buf;
+	int ret, len;
+
+	if (!metadata) {
+		/*
+		 * Querying the size is inherently racey, but
+		 * EXT_external_objects expects the app to confirm
+		 * via device and driver UUIDs that the exporter and
+		 * importer versions match.  All we can do from the
+		 * kernel side is check the length under obj lock
+		 * when userspace tries to retrieve the metadata
+		 */
+		*metadata_size = msm_obj->metadata_size;
+		return 0;
+	}
+
+	ret = msm_gem_lock_interruptible(obj);
+	if (ret)
+		return ret;
+
+	/* Avoid copy_to_user() under gem obj lock: */
+	len = msm_obj->metadata_size;
+	buf = kmemdup(msm_obj->metadata, len, GFP_KERNEL);
+
+	msm_gem_unlock(obj);
+
+	if (*metadata_size < len) {
+		ret = -ETOOSMALL;
+	} else if (copy_to_user(metadata, buf, len)) {
+		ret = -EFAULT;
+	} else {
+		*metadata_size = len;
+	}
+
+	kfree(buf);
+
+	return 0;
+}
+
 static int msm_ioctl_gem_info(struct drm_device *dev, void *data,
 		struct drm_file *file)
 {
@@ -568,6 +648,8 @@ static int msm_ioctl_gem_info(struct drm_device *dev, void *data,
 		break;
 	case MSM_INFO_SET_NAME:
 	case MSM_INFO_GET_NAME:
+	case MSM_INFO_SET_METADATA:
+	case MSM_INFO_GET_METADATA:
 		break;
 	default:
 		return -EINVAL;
@@ -630,6 +712,14 @@ static int msm_ioctl_gem_info(struct drm_device *dev, void *data,
 				ret = -EFAULT;
 		}
 		break;
+	case MSM_INFO_SET_METADATA:
+		ret = msm_ioctl_gem_info_set_metadata(
+			obj, u64_to_user_ptr(args->value), args->len);
+		break;
+	case MSM_INFO_GET_METADATA:
+		ret = msm_ioctl_gem_info_get_metadata(
+			obj, u64_to_user_ptr(args->value), &args->len);
+		break;
 	}
 
 	drm_gem_object_put(obj);

drivers/gpu/drm/msm/msm_gem.c

@@ -1058,6 +1058,7 @@ static void msm_gem_free_object(struct drm_gem_object *obj)
 
 	drm_gem_object_release(obj);
 
+	kfree(msm_obj->metadata);
 	kfree(msm_obj);
 }
 

drivers/gpu/drm/msm/msm_gem.h

@@ -108,6 +108,10 @@ struct msm_gem_object {
 
 	char name[32]; /* Identifier to print for the debugfs files */
 
+	/* userspace metadata backchannel */
+	void *metadata;
+	u32 metadata_size;
+
 	/**
 	 * pin_count: Number of times the pages are pinned
 	 *

include/uapi/drm/msm_drm.h

@@ -139,6 +139,8 @@ struct drm_msm_gem_new {
 #define MSM_INFO_GET_NAME	0x03   /* get debug name, returned by pointer */
 #define MSM_INFO_SET_IOVA	0x04   /* set the iova, passed by value */
 #define MSM_INFO_GET_FLAGS	0x05   /* get the MSM_BO_x flags */
+#define MSM_INFO_SET_METADATA	0x06   /* set userspace metadata */
+#define MSM_INFO_GET_METADATA	0x07   /* get userspace metadata */
 
 struct drm_msm_gem_info {
 	__u32 handle;         /* in */