RISC-V Summit

The specification of the IOPMP, I/O Physical Memory Protection Unit, is nearing stability, making it an opportune moment to introduce the IOPMP programming model to users. This presentation will demonstrate the bottom-up programming model of IOPMP in M-mode, H-mode, and VS/S-mode.
In M mode, we utilize a native library, libiopmp, while H/S/VS-mode employs the SBI for IOPMP with necessary security checks. Within libiopmp, we will explore how to group the regions of a specific device into a memory domain, which can be easily switched and shared. This clarifies why IOPMP prefers the per-device association programming model over ARM's per-rule association model.

The SBI, positioned above the libiopmp, allows the other modes to manipulate the IOPMP. A hypervisor should be able to allocate devices for a guest OS. IOPMP's memory domain offers a convenient method for associating devices with a specific guest OS.

In H/S mode, hot-plug devices may necessitate IOPMP updates. In VS mode, a guest OS typically lacks knowledge about the physical memory, so the IOPMP's updates are generally transparent. Software in the higher privileged modes helps to manipulate IOPMP(s) behind guest OS requests.