Code to allow access to MAP_SHARED memory in AArch64 Linux kernel

I need a driver to allow access to an *existing* MAP_SHARED memory region (at a fixed virtual address) to another process (given its PID) through ioctl calls. I need this to be done by actually making a vm_area_struct in the target process as if it was created in that process from the beginning (not by mapping another device to the same physical memory region).

The code should not use any Linux APIs that perform a lot of operations (because I need this for educational purposes).

Contact me if you need more details.