Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751210AbWIYGD4 (ORCPT ); Mon, 25 Sep 2006 02:03:56 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751298AbWIYGD4 (ORCPT ); Mon, 25 Sep 2006 02:03:56 -0400 Received: from ozlabs.org ([203.10.76.45]:1711 "EHLO ozlabs.org") by vger.kernel.org with ESMTP id S1751210AbWIYGDz (ORCPT ); Mon, 25 Sep 2006 02:03:55 -0400 Subject: Re: [PATCH 5/7] Use %gs for per-cpu sections in kernel From: Rusty Russell To: Jeremy Fitzhardinge Cc: Andi Kleen , lkml - Kernel Mailing List , virtualization In-Reply-To: <45176865.7020300@goop.org> References: <1158925861.26261.3.camel@localhost.localdomain> <1158925997.26261.6.camel@localhost.localdomain> <1158926106.26261.8.camel@localhost.localdomain> <1158926215.26261.11.camel@localhost.localdomain> <1158926308.26261.14.camel@localhost.localdomain> <1158926386.26261.17.camel@localhost.localdomain> <4514663E.5050707@goop.org> <1158985882.26261.60.camel@localhost.localdomain> <45172AC8.2070701@goop.org> <1159146974.26986.30.camel@localhost.localdomain> <45173287.8070204@goop.org> <1159152678.26986.38.camel@localhost.localdomain> <45176865.7020300@goop.org> Content-Type: text/plain Date: Mon, 25 Sep 2006 16:03:52 +1000 Message-Id: <1159164232.26986.59.camel@localhost.localdomain> Mime-Version: 1.0 X-Mailer: Evolution 2.6.1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1319 Lines: 40 On Sun, 2006-09-24 at 22:25 -0700, Jeremy Fitzhardinge wrote: > The %gs:per_cpu__foo addressing mode still calculates > 0xbcef00+0xc0433800, which is still a subtraction. My essential point > is that *all* kernel addresses (=kernel symbols) are negative, so using > them as an offset from a segment base (any segment base) is a > subtraction, which requires a 4G limit. I don't think so. There's *never* address subtraction, there's sometimes 32 bit wrap (glibc uses this to effect subtraction, sure). But there's no wrap here. To test, I changed the following: --- smpboot.c.~8~ 2006-09-25 15:51:50.000000000 +1000 +++ smpboot.c 2006-09-25 16:00:36.000000000 +1000 @@ -926,8 +926,9 @@ unsigned long per_cpu_off) { unsigned limit, flags; + extern char __per_cpu_end[]; - limit = (1 << 20); + limit = PAGE_ALIGN((long)__per_cpu_end) >> PAGE_SHIFT; flags = 0x8; /* 4k granularity */ /* present read-write data segment */ Works fine... Hope that clarifies! Rusty. -- Help! Save Australia from the worst of the DMCA: http://linux.org.au/law - 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/