Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S935876Ab3DJAx6 (ORCPT ); Tue, 9 Apr 2013 20:53:58 -0400 Received: from hrndva-omtalb.mail.rr.com ([71.74.56.122]:16740 "EHLO hrndva-omtalb.mail.rr.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1764843Ab3DJAx5 (ORCPT ); Tue, 9 Apr 2013 20:53:57 -0400 X-Authority-Analysis: v=2.0 cv=aOZyWMBm c=1 sm=0 a=rXTBtCOcEpjy1lPqhTCpEQ==:17 a=mNMOxpOpBa8A:10 a=5SG0PmZfjMsA:10 a=IkcTkHD0fZMA:10 a=meVymXHHAAAA:8 a=iDqrtN4IwfAA:10 a=Zfl1aey8p3cdzKZLxGgA:9 a=QEXdDO2ut3YA:10 a=j-qZ3nskaGKCfgvn:21 a=jNzDk3VDkK37ZKSw:21 a=rXTBtCOcEpjy1lPqhTCpEQ==:117 X-Cloudmark-Score: 0 X-Authenticated-User: X-Originating-IP: 74.67.115.198 Message-ID: <1365555234.25498.91.camel@gandalf.local.home> Subject: Re: Readonly GDT From: Steven Rostedt To: "H. Peter Anvin" Cc: Eric Northup , Kees Cook , "kernel-hardening@lists.openwall.com" , Ingo Molnar , LKML , "x86@kernel.org" , Konrad Rzeszutek Wilk , Jeremy Fitzhardinge , Marcelo Tosatti , Alex Shi , Borislav Petkov , Alexander Duyck , Frederic Weisbecker , "Paul E. McKenney" , "xen-devel@lists.xensource.com" , "virtualization@lists.linux-foundation.org" , Dan Rosenberg , Julien Tinnes , Will Drewry Date: Tue, 09 Apr 2013 20:53:54 -0400 In-Reply-To: <5164B5BD.5050702@zytor.com> References: <20130408224328.GA17641@www.outflux.net> <51634935.9010905@zytor.com> <51645D6F.7070705@zytor.com> <51646054.3090509@zytor.com> <5164B5BD.5050702@zytor.com> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.4.4-2 Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1148 Lines: 32 On Tue, 2013-04-09 at 17:43 -0700, H. Peter Anvin wrote: > OK, thinking about the GDT here. > > The GDT is quite small -- 256 bytes on i386, 128 bytes on x86-64. As > such, we probably don't want to allocate a full page to it for only > that. This means that in order to create a readonly mapping we have to > pack GDTs from different CPUs together in the same pages, *or* we > tolerate that other things on the same page gets reflected in the same > mapping. What about grouping via nodes? > > However, the packing solution has the advantage of reducing address > space consumption which matters on 32 bits: even on i386 we can easily > burn a megabyte of address space for 4096 processors, but burning 16 > megabytes starts to hurt. Having 4096 32 bit processors, you deserve what you get. ;-) -- Steve > > It would be important to measure the performance impact on task switch, > though. -- 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/