Date: Sat, 6 Mar 1999 19:19:34 +0000 (GMT) From: Terry Lambert <tlambert@primenet.com> To: dillon@apollo.backplane.com (Matthew Dillon) Cc: hasty@rah.star-gate.com, tlambert@primenet.com, dyson@iquest.net, dick@tar.com, jplevyak@inktomi.com, hackers@FreeBSD.ORG Subject: Re: lockf and kernel threads Message-ID: <199903061919.MAA09233@usr06.primenet.com> In-Reply-To: <199903051841.KAA49799@apollo.backplane.com> from "Matthew Dillon" at Mar 5, 99 10:41:07 am
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> :Thats probably true however for delivery of an AST I don't thing that we > :need priviliged instructions --- I could be wrong. > > Little things like, ohhhhh disabling interrupts. Accessing the MMU > registers, flushing the TLB, etc..... believe me, ring 1 and ring 2 > is utterly useless for anything FreeBSD wants to run in supervisor mode. Uh, if you ran the AST target function in supervisor mode, it would be a nice truck-size hole in the security model. The distinction between ring 2 and ring 3 is useful primarily for drawing a border between calls to user code from the kernel vs. calls to user code by the user. In both cases, it's user code that's executing: unpriviledged code. I think you are maybe being confused with "installed images" and "symbionts", which generally did *not* run at the same level as AST's. I can (and I think Wes Peters can) dig up a reference to a VMS-like OS educational implementation for which the University we went to had source that implemented a four-tier protection menchanism in general, and AST's from kernel to user, in particular. Terry Lambert terry@lambert.org --- Any opinions in this posting are my own and not those of my present or previous employers. To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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