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Path: sserve!newshost.anu.edu.au!munnari.oz.au!news.Hawaii.Edu!ames!saimiri.primate.wisc.edu!news.larc.nasa.gov!darwin.sura.net!howland.reston.ans.net!math.ohio-state.edu!caen!usenet.coe.montana.edu!decwrl!cronkite.cisco.com!cisco.com!vandys From: vandys@cisco.com (Andrew Valencia) Newsgroups: comp.unix.bsd Subject: Copyout fix for i386 Date: 2 Oct 93 00:36:40 GMT Organization: cisco Systems Lines: 14 Message-ID: <vandys.749522200@cisco.com> NNTP-Posting-Host: glare.cisco.com Hi, There seems to be a classic problem with all i386 BSDen. The problem is that an i386 will allow ring 0 to write through a PTE with the read-only bit turned on. The usual workaround is to manually inspect each PTE in routines like copyout--slow! I have heard talk about using the RPL field of the segment descriptor, and would like to know if it works, and if there are any other "gotchas". That is, if I'm running in ring 0, make a write reference through a descriptor with RPL 3, will it trap instead of completing the write if the PTE is valid but read-only? Thanks in advance for any experience you might have had in this area! Andy Valencia