Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1763959AbYFFIJK (ORCPT ); Fri, 6 Jun 2008 04:09:10 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754018AbYFFIIv (ORCPT ); Fri, 6 Jun 2008 04:08:51 -0400 Received: from gw.goop.org ([64.81.55.164]:37515 "EHLO mail.goop.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752928AbYFFIIt (ORCPT ); Fri, 6 Jun 2008 04:08:49 -0400 Message-ID: <4848F068.5060807@goop.org> Date: Fri, 06 Jun 2008 09:08:08 +0100 From: Jeremy Fitzhardinge User-Agent: Thunderbird 2.0.0.14 (X11/20080501) MIME-Version: 1.0 To: Arjan van de Ven CC: Ingo Molnar , x86@kernel.org, Linux Kernel Mailing List , Jan Beulich , Stable Kernel Subject: Re: [PATCH] x86: set PAE PHYSICAL_MASK_SHIFT to match 64-bit References: <4848046A.5060006@goop.org> <20080605214536.0e289ebb@infradead.org> In-Reply-To: <20080605214536.0e289ebb@infradead.org> X-Enigmail-Version: 0.95.6 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: 1297 Lines: 32 Arjan van de Ven wrote: > On Thu, 05 Jun 2008 16:21:14 +0100 > Jeremy Fitzhardinge wrote: > > >> When a 64-bit x86 processor runs in 32-bit PAE mode, a pte can >> potentially have the same number of physical address bits as the >> 64-bit host ("Enhanced Legacy PAE Paging"). >> >> > > the problem on 32 bit is that if you have that much ram, you run out of > lowmem FAST.... so you have bigger problems. > Sure, you'd have to be barking mad to give a 32-bit system 2^40 bytes of RAM. But under Xen the host's physical addresses are used in guest pagetables, so you could have a reasonably sized 32-bit PAE Xen guest be exposed to huge host physical addresses. But the basic point is that, given that Enhanced Legacy PAE Paging exists, 36-bits is not correct, so we should fix it. And if the platform allows addressable hardware to be physically discontigious - either memory or devices - then you may end up using large numbers of physical bits without having a stupid amount of memory actually present. J -- 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/