NIOS II Multi-Processor System's On-chip Memory

It's all set up in the hardware through multi-mastering. In Qsys, connect all the cores to the on-chip memory. The base address for the memory for each core can be the same or unique for each one. It doesn't matter because each master has its own memory map. Then, in the BSP editor for each core, make sure the linker script is set up for the correct offset to the appropriate location in the memory.