Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751684AbWIYXdT (ORCPT ); Mon, 25 Sep 2006 19:33:19 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751688AbWIYXdT (ORCPT ); Mon, 25 Sep 2006 19:33:19 -0400 Received: from ozlabs.org ([203.10.76.45]:15040 "EHLO ozlabs.org") by vger.kernel.org with ESMTP id S1751684AbWIYXdS (ORCPT ); Mon, 25 Sep 2006 19:33:18 -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: <45177664.3060103@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> <1159164232.26986.59.camel@localhost.localdomain> <45177664.3060103@goop.org> Content-Type: text/plain Date: Tue, 26 Sep 2006 09:33:14 +1000 Message-Id: <1159227195.26986.68.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: 1341 Lines: 40 On Sun, 2006-09-24 at 23:25 -0700, Jeremy Fitzhardinge wrote: > Rusty Russell wrote: > > 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. > > > Hm, I guess, so long as you assume the kernel data segment is always > below the kernel heap. Agreed, we should BUG_ON() in case anyone ever changes this... I will create a patch for this... > > 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; > > > limit is a size, rather than the end address, so this isn't quite right. I think it's OK. For every "%gs:var", var will be less than __per_cpu_end. Thanks! 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/