On Tue, Sep 8, 2020 at 3:32 PM Matthew Garrett <mj...@google.com> wrote: > > On Tue, Sep 8, 2020 at 1:35 PM Andy Lutomirski <l...@amacapital.net> wrote: > > > Undervolting is a bit different. It’s a genuinely useful configuration that > > can affect system stability. In general, I think it should be allowed, and > > it should have a real driver in tree. > > Agree that this should be a proper driver rather than permitting > arbitrary poking (especially if this isn't an architecturally defined > MSR - there's no guarantee that it'll have the same functionality > everywhere).
After looking at the code for intel-undervolt a bit, that definitely needs kernel or even firmware support. That MSR really is a mailbox. You write commands to it and read responses. There's no way that user code can have adequate locking.
