Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758503AbYHGW6l (ORCPT ); Thu, 7 Aug 2008 18:58:41 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754249AbYHGW6e (ORCPT ); Thu, 7 Aug 2008 18:58:34 -0400 Received: from terminus.zytor.com ([198.137.202.10]:54607 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753288AbYHGW6d (ORCPT ); Thu, 7 Aug 2008 18:58:33 -0400 Message-ID: <489B7DFE.5010402@kernel.org> Date: Thu, 07 Aug 2008 15:58:06 -0700 From: "H. Peter Anvin" Organization: Linux Kernel Organization, Inc. User-Agent: Thunderbird 2.0.0.14 (X11/20080501) MIME-Version: 1.0 To: Linus Torvalds CC: Zachary Amsden , Alok Kataria , Ingo Molnar , the arch/x86 maintainers , LKML Subject: Re: [PATCH]Fix broken VMI in 2.6.27-rc.. References: <1218136365.23770.52.camel@alok-dev1> <489B6710.9000604@kernel.org> <1218144438.20178.336.camel@bodhitayantram.eng.vmware.com> <489B6A5C.8030400@kernel.org> <1218145344.20178.347.camel@bodhitayantram.eng.vmware.com> <489B6E83.7000202@kernel.org> <1218146154.20178.352.camel@bodhitayantram.eng.vmware.com> <489B7470.5030408@kernel.org> In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1511 Lines: 34 Linus Torvalds wrote: > > On Thu, 7 Aug 2008, H. Peter Anvin wrote: >> The only way I can see around that, though, is to move the 1:1 mapping base up >> by 2/4 MB (for PAE/no PAE, respectively) and put the fixmap area there. Kind >> of sucks, but would be doable. > > So if the address isn't fixed, you'll end up with an indirect pointer, and > it would likely be much better to just use a fixed direct pointer that is > not at the top. > > And anything that is within the top 31 bits of the address space should > generate the same good code, since the fixed offset is always going to be > a 32-bit thing anyway. So moving the FIXMAP area down by 4MB sounds like a > fine thing to do with no real downside, if it then means that we don't > need to move the FIXMAP area at all. > > Hmm? Am I missing something? Just moving it down by 4 MB doesn't help, since the VMI guys want as much as 64 MB, which is half the standard vmalloc area and hence too much address space lost. We can't put it at the bottom of the vmalloc area, since that boundary is not fixed, either. The one remaining fixed boundary in the machine is the kernel-userspace boundary. Hence moving the 1:1 area up by one PDE unit and sticking the fixmap area in that region. -hpa -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/