riscv-pk

Please don't spread misinformation. RISC-V has a well-thought out machine layer which is open source in all existing implementations[1]. You can easily modify the M layer if it's interfering with the performance or security of your OS. The virtualization extension hasn't been finalized (but they are working with key KVM people), but it will perform a lot better than a theoretically pure self-virtualizable ISA. [1] https://github.com/riscv/riscv-pk

On your second question about real-time support, I think the answer is (probably) yes although it depends a bit on precisely what you mean by "real time". I'm assuming you mean as a hard real time microcontroller. First off there is an Intel SMM-like layer (M mode) running under the operating system. Unlike Intel it's all open source. So if you find that something in M mode is taking too long and disturbing your real time guarantees, you at least have a hope of fixing it. Obviously Linux is no use for hard real time, but in the HiFive Unleashed board there is a separate RV32 core on the side which actually does nothing except spinning in M mode. It literally runs this loop: https://github.com/riscv/riscv-pk/blob/600ff370c65ba99d2103a... You could have this spare core do anything you want while running Linux on the application cores.