drm: Add DRM prime interface to reassign GEM handle

CRIU restore of drm buffer objects requires the ability to create
or import a buffer object with a specific gem handle.

Add new drm ioctl DRM_IOCTL_GEM_CHANGE_HANDLE, which takes
the gem handle of an object and moves that object to a
specified new gem handle.

This ioctl needs to call drm_prime_remove_buf_handle,
but that function acquires the prime lock, which the ioctl
needs to hold for other purposes.

Make drm_prime_remove_buf_handle not acquire the prime lock,
and change its other caller to reflect this.

The rest of the kernel patches required to enable CRIU can be
found at
https://lore.kernel.org/dri-devel/20250617194536.538681-1-David.Francis@amd.com/

v2 - Move documentation to UAPI headers
v3 - Always return 0 on success

Signed-off-by: David Francis <David.Francis@amd.com>
Acked-by: Felix Kuehling <felix.kuehling@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Christian König <christian.koenig@amd.com>
Link: https://lore.kernel.org/r/20250717143556.857893-2-David.Francis@amd.com

drivers/gpu/drm/drm_gem.c

@@ -283,7 +283,12 @@ drm_gem_object_release_handle(int id, void *ptr, void *data)
 	if (obj->funcs->close)
 		obj->funcs->close(obj, file_priv);
 
+	mutex_lock(&file_priv->prime.lock);
+
 	drm_prime_remove_buf_handle(&file_priv->prime, id);
+
+	mutex_unlock(&file_priv->prime.lock);
+
 	drm_vma_node_revoke(&obj->vma_node, file_priv);
 
 	drm_gem_object_handle_put_unlocked(obj);
@@ -934,6 +939,57 @@ drm_gem_open_ioctl(struct drm_device *dev, void *data,
 	return ret;
 }
 
+int drm_gem_change_handle_ioctl(struct drm_device *dev, void *data,
+				struct drm_file *file_priv)
+{
+	struct drm_gem_change_handle *args = data;
+	struct drm_gem_object *obj;
+	int ret;
+
+	if (!drm_core_check_feature(dev, DRIVER_GEM))
+		return -EOPNOTSUPP;
+
+	obj = drm_gem_object_lookup(file_priv, args->handle);
+	if (!obj)
+		return -ENOENT;
+
+	if (args->handle == args->new_handle)
+		return 0;
+
+	mutex_lock(&file_priv->prime.lock);
+
+	spin_lock(&file_priv->table_lock);
+	ret = idr_alloc(&file_priv->object_idr, obj,
+		args->new_handle, args->new_handle + 1, GFP_NOWAIT);
+	spin_unlock(&file_priv->table_lock);
+
+	if (ret < 0)
+		goto out_unlock;
+
+	if (obj->dma_buf) {
+		ret = drm_prime_add_buf_handle(&file_priv->prime, obj->dma_buf, args->new_handle);
+		if (ret < 0) {
+			spin_lock(&file_priv->table_lock);
+			idr_remove(&file_priv->object_idr, args->new_handle);
+			spin_unlock(&file_priv->table_lock);
+			goto out_unlock;
+		}
+
+		drm_prime_remove_buf_handle(&file_priv->prime, args->handle);
+	}
+
+	ret = 0;
+
+	spin_lock(&file_priv->table_lock);
+	idr_remove(&file_priv->object_idr, args->handle);
+	spin_unlock(&file_priv->table_lock);
+
+out_unlock:
+	mutex_unlock(&file_priv->prime.lock);
+
+	return ret;
+}
+
 /**
  * drm_gem_open - initializes GEM file-private structures at devnode open time
  * @dev: drm_device which is being opened by userspace

drivers/gpu/drm/drm_internal.h

@@ -85,6 +85,8 @@ int drm_prime_fd_to_handle_ioctl(struct drm_device *dev, void *data,
 
 void drm_prime_init_file_private(struct drm_prime_file_private *prime_fpriv);
 void drm_prime_destroy_file_private(struct drm_prime_file_private *prime_fpriv);
+int drm_prime_add_buf_handle(struct drm_prime_file_private *prime_fpriv,
+			     struct dma_buf *dma_buf, uint32_t handle);
 void drm_prime_remove_buf_handle(struct drm_prime_file_private *prime_fpriv,
 				 uint32_t handle);
 
@@ -168,6 +170,8 @@ int drm_gem_close_ioctl(struct drm_device *dev, void *data,
 			struct drm_file *file_priv);
 int drm_gem_flink_ioctl(struct drm_device *dev, void *data,
 			struct drm_file *file_priv);
+int drm_gem_change_handle_ioctl(struct drm_device *dev, void *data,
+				struct drm_file *file_priv);
 int drm_gem_open_ioctl(struct drm_device *dev, void *data,
 		       struct drm_file *file_priv);
 void drm_gem_open(struct drm_device *dev, struct drm_file *file_private);

drivers/gpu/drm/drm_ioctl.c

@@ -653,6 +653,7 @@ static const struct drm_ioctl_desc drm_ioctls[] = {
 	DRM_IOCTL_DEF(DRM_IOCTL_GEM_CLOSE, drm_gem_close_ioctl, DRM_RENDER_ALLOW),
 	DRM_IOCTL_DEF(DRM_IOCTL_GEM_FLINK, drm_gem_flink_ioctl, DRM_AUTH),
 	DRM_IOCTL_DEF(DRM_IOCTL_GEM_OPEN, drm_gem_open_ioctl, DRM_AUTH),
+	DRM_IOCTL_DEF(DRM_IOCTL_GEM_CHANGE_HANDLE, drm_gem_change_handle_ioctl, DRM_RENDER_ALLOW),
 
 	DRM_IOCTL_DEF(DRM_IOCTL_MODE_GETRESOURCES, drm_mode_getresources, 0),
 

drivers/gpu/drm/drm_prime.c

@@ -93,7 +93,7 @@ struct drm_prime_member {
 	struct rb_node handle_rb;
 };
 
-static int drm_prime_add_buf_handle(struct drm_prime_file_private *prime_fpriv,
+int drm_prime_add_buf_handle(struct drm_prime_file_private *prime_fpriv,
 				    struct dma_buf *dma_buf, uint32_t handle)
 {
 	struct drm_prime_member *member;
@@ -190,8 +190,6 @@ void drm_prime_remove_buf_handle(struct drm_prime_file_private *prime_fpriv,
 {
 	struct rb_node *rb;
 
-	mutex_lock(&prime_fpriv->lock);
-
 	rb = prime_fpriv->handles.rb_node;
 	while (rb) {
 		struct drm_prime_member *member;
@@ -210,8 +208,6 @@ void drm_prime_remove_buf_handle(struct drm_prime_file_private *prime_fpriv,
 			rb = rb->rb_left;
 		}
 	}
-
-	mutex_unlock(&prime_fpriv->lock);
 }
 
 void drm_prime_init_file_private(struct drm_prime_file_private *prime_fpriv)

include/uapi/drm/drm.h

@@ -625,6 +625,21 @@ struct drm_gem_open {
 	__u64 size;
 };
 
+/**
+ * struct drm_gem_change_handle - Argument for &DRM_IOCTL_GEM_CHANGE_HANDLE ioctl.
+ * @handle: The handle of a gem object.
+ * @new_handle: An available gem handle.
+ *
+ * This ioctl changes the handle of a GEM object to the specified one.
+ * The new handle must be unused. On success the old handle is closed
+ * and all further IOCTL should refer to the new handle only.
+ * Calls to DRM_IOCTL_PRIME_FD_TO_HANDLE will return the new handle.
+ */
+struct drm_gem_change_handle {
+	__u32 handle;
+	__u32 new_handle;
+};
+
 /**
  * DRM_CAP_DUMB_BUFFER
  *
@@ -1309,6 +1324,14 @@ extern "C" {
  */
 #define DRM_IOCTL_SET_CLIENT_NAME	DRM_IOWR(0xD1, struct drm_set_client_name)
 
+/**
+ * DRM_IOCTL_GEM_CHANGE_HANDLE - Move an object to a different handle
+ *
+ * Some applications (notably CRIU) need objects to have specific gem handles.
+ * This ioctl changes the object at one gem handle to use a new gem handle.
+ */
+#define DRM_IOCTL_GEM_CHANGE_HANDLE    DRM_IOWR(0xD2, struct drm_gem_change_handle)
+
 /*
  * Device specific ioctls should only be in their respective headers
  * The device specific ioctl range is from 0x40 to 0x9f.