Date: Sat, 27 Sep 1997 18:19:02 -0500 (EST) From: "John S. Dyson" <toor@dyson.iquest.net> To: weeteck@eecs.umich.edu (Wee Teck Ng) Cc: freebsd-hackers@FreeBSD.ORG Subject: Re: using vm_map_protect on Pentium PC Message-ID: <199709272319.SAA12614@dyson.iquest.net> In-Reply-To: <199709270523.BAA07578@singapore.eecs.umich.edu> from Wee Teck Ng at "Sep 27, 97 01:23:44 am"
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Wee Teck Ng said: > hi all, > > we are heavily utilising VM protection (vm_map_prot) on 2.2-stable, > and found that it doesn't work well on Pentium processor. specifically, > when using vm_map_prot to change a page's protection from VM_PROT_READ > to VM_PROT_ALL, only the vm map is updated. > That should be okay. > > pmap_protect does not reset > the pte to writeable (i.e. PG_RW). this will not work on pentium processor, > since page level protection is enforced by the processor (against kernel > access) when WP flag of CR0 is set. > > i've noticed that FreeBSD-current has fixed this problem. my questions are: > 1) is there a 2.x release with a Pentium-compatible VM system? > 2) how stable is 3.0 is for non SMP machines? > Actually, the VM system uses lazy techniques. As soon as you cause a (write) fault, the page SHOULD have it's protections corrected. -- John dyson@freebsd.org jdyson@nc.com
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