Re: Proposal: Delegating Exceptions from VS-mode or VU-mode to U-mode


Jonathan Behrens <behrensj@...>
 


On Sat, Sep 19, 2020 at 5:29 AM Gernot via lists.riscv.org <gernot.heiser=data61.csiro.au@...> wrote:
User-level drivers are a core properties of (well-designed) microkernels, and microkernels are pretty much the only choice for safety- and security-critical systems, and the only kind of OS that is feasible to prove correct (see seL4).

And if you run drivers in user mode, then being able to route interrupts directly to the user-level handlers without invoking the kernel would seem to pretty much eliminate the performance disadvantage microkernels have compared to Linux. In fact, my immediate reaction seeing this extension was “yeah!”.

You can achieve the same thing using the hypervisor extension analogously to how M/U systems can avoid user-level interrupts by switching to M/S/U. Instead of running the kernel in S-mode and drivers in U-mode, run the kernel in HS-mode and the drivers in VS-mode.

Jonathan

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