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Date: Wed, 23 Nov 2005 11:12:01 -0800
From: "H. Peter Anvin" <hpa@zytor.com>
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To: Linus Torvalds <torvalds@osdl.org>
CC: Alan Cox <alan@lxorguk.ukuu.org.uk>, Andi Kleen <ak@suse.de>,
       Gerd Knorr <kraxel@suse.de>, Dave Jones <davej@redhat.com>,
       Zachary Amsden <zach@vmware.com>, Pavel Machek <pavel@ucw.cz>,
       Andrew Morton <akpm@osdl.org>,
       Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
       Zwane Mwaikambo <zwane@arm.linux.org.uk>,
       Pratap Subrahmanyam <pratap@vmware.com>,
       Christopher Li <chrisl@vmware.com>,
       "Eric W. Biederman" <ebiederm@xmission.com>,
       Ingo Molnar <mingo@elte.hu>
Subject: Re: [patch] SMP alternatives
References: <Pine.LNX.4.64.0511131118020.3263@g5.osdl.org>  <Pine.LNX.4.64.0511131210570.3263@g5.osdl.org> <4378A7F3.9070704@suse.de>  <Pine.LNX.4.64.0511141118000.3263@g5.osdl.org> <4379ECC1.20005@suse.de>  <437A0649.7010702@suse.de> <437B5A83.8090808@suse.de>  <438359D7.7090308@suse.de> <p7364qjjhqx.fsf@verdi.suse.de>  <1132764133.7268.51.camel@localhost.localdomain>  <20051123163906.GF20775@brahms.suse.de> <1132766489.7268.71.camel@localhost.localdomain> <Pine.LNX.4.64.0511230858180.13959@g5.osdl.org> <4384AECC.1030403@zytor.com> <Pine.LNX.4.64.0511231031350.13959@g5.osdl.org>
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Linus Torvalds wrote:
> 
> Of course, if it's in one of the low 12 bits of %cr3, there would have to 
> be a "enable this bit" in %cr4 or something. Historically, you could write 
> any crap in the low bits, I think.
> 

No, most of them are RAZ, but there are at least a couple of bits which 
have effect (e.g. caching of the page tables.)

However, with PAE there aren't really a whole lot of unused bits in CR3.

	-hpa
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