v4.19.13 snapshot.
diff --git a/include/linux/mmu_context.h b/include/linux/mmu_context.h
new file mode 100644
index 0000000..d9a543a
--- /dev/null
+++ b/include/linux/mmu_context.h
@@ -0,0 +1,17 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _LINUX_MMU_CONTEXT_H
+#define _LINUX_MMU_CONTEXT_H
+
+#include <asm/mmu_context.h>
+
+struct mm_struct;
+
+void use_mm(struct mm_struct *mm);
+void unuse_mm(struct mm_struct *mm);
+
+/* Architectures that care about IRQ state in switch_mm can override this. */
+#ifndef switch_mm_irqs_off
+# define switch_mm_irqs_off switch_mm
+#endif
+
+#endif