Resolved! RPMSG SDB cached buffer
We follow this: https://wiki.st.com/stm32mpu/wiki/How_to_exchange_large_data_buffers_with_the_coprocessor_-_principle and this: https://wiki.st.com/stm32mpu/wiki/How_to_exchange_large_data_buffers_with_the_coprocessor_-_example#Linux_driversarticles...