On Sun, Dec 2, 2012 at 5:48 PM, Peter Gavin <[email protected]> wrote: > On Sun, Dec 2, 2012 at 4:38 PM, Matthew Hicks <[email protected]> wrote: >> >> This is a bad idea. You want to make the processor fully >> virtualizable. This requires the ability for a hypervisor to >> interpose on an unmodified operating system. For this to work, the >> hypervisor changes the operating system privilege to 0 (user mode) and >> when the operating system accesses or modifies privileged state, an >> exception triggers and the hypervisor takes over. With your proposal, >> the hypervisor would never know and the system would collapse. > > > I believe (now that I've done some reading) we should also specify that > l.rfe traps if executed in user mode. > > -Pete
More generally (as you stated in a private email), any usermode use of a privileged instruction should trap. ---Matthew Hicks _______________________________________________ OpenRISC mailing list [email protected] http://lists.openrisc.net/listinfo/openrisc
