Date: Thu, 23 Apr 1998 12:32:48 -0400 (EDT) From: "David E. Cross" <dec@phoenix.its.rpi.edu> To: Jonathan Lemon <jlemon@americantv.com> Cc: Alfred Perlstein <perlsta@fang.cs.sunyit.edu>, freebsd-hackers@FreeBSD.ORG Subject: Re: Protected mode instructions which reduce to noop. Message-ID: <Pine.BSF.3.96.980423122909.12562B-100000@phoenix.its.rpi.edu> In-Reply-To: <19980423103837.32719@right.PCS>
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> AFAIK, all privileged instructions, when executed in a non-supervisor > context, generate an exception of some sort. This applies to the > sti, cli, popfl, I/O family of instructions, as well as those insns > which diddle with the control registers. > > What VM type architecture were you referring to? I am referring to IBM's VM operating system. and here is the original message from -hackers from nov-1997: From: "Eric J. Schwertfeger" <ejs@bfd.com> To: gad@eclipse.its.rpi.edu cc: hackers@FreeBSD.ORG Subject: Re: Virtual Intel Machines? On Wed, 12 Nov 1997, Garance A Drosehn wrote: > In the land of IBM mainframes, there's an operating system (of > sorts) called VM. This is an operating system which lets you run > multiple operating systems on a single machine, at the same time. > VM can allocate devices between the running systems, so that one > running OS sees a given hard disk (for example), but no other > operating systems can possibly get to that hard disk. > > What I was wondering is if something similar could be done with > Intel-ish chips? I realize this wouldn't be a trivial thing to > write, but it'd be mighty convenient to have in some circumstances > (at least in an academic setting). Not in the strictest sense, because Intel, in their infinite wisdom, decided that certain privledged instructions, if executed in an unprivledged state, would not trap, but rather reduce to a NOP. Hence, the VM equiv can't trap the OS's attempt to do this, and make it happen, given appropriate permissions. -- David Cross To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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