v4.19.13 snapshot.
diff --git a/arch/arm/include/asm/idmap.h b/arch/arm/include/asm/idmap.h
new file mode 100644
index 0000000..73ba956
--- /dev/null
+++ b/arch/arm/include/asm/idmap.h
@@ -0,0 +1,15 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __ASM_IDMAP_H
+#define __ASM_IDMAP_H
+
+#include <linux/compiler.h>
+#include <asm/pgtable.h>
+
+/* Tag a function as requiring to be executed via an identity mapping. */
+#define __idmap __section(.idmap.text) noinline notrace
+
+extern pgd_t *idmap_pgd;
+
+void setup_mm_for_reboot(void);
+
+#endif /* __ASM_IDMAP_H */