From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753907AbbHMVHQ (ORCPT ); Thu, 13 Aug 2015 17:07:16 -0400 Received: from terminus.zytor.com ([198.137.202.10]:58773 "EHLO mail.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752222AbbHMVHO (ORCPT ); Thu, 13 Aug 2015 17:07:14 -0400 Message-ID: <55CD06A4.2090100@zytor.com> Date: Thu, 13 Aug 2015 14:05:40 -0700 From: "H. Peter Anvin" User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.7.0 MIME-Version: 1.0 To: Andy Lutomirski , Peter Zijlstra , Steven Rostedt CC: "security@kernel.org" , X86 ML , Borislav Petkov , Sasha Levin , linux-kernel@vger.kernel.org, Konrad Rzeszutek Wilk , Boris Ostrovsky , Andrew Cooper , Jan Beulich , xen-devel , stable@vger.kernel.org Subject: Re: [PATCH v5 2/4] x86/ldt: Make modify_ldt synchronous References: <1f1e8e0367408585694132a0e8693d157959ce30.1438061139.git.luto@kernel.org> In-Reply-To: <1f1e8e0367408585694132a0e8693d157959ce30.1438061139.git.luto@kernel.org> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 07/27/2015 10:29 PM, Andy Lutomirski wrote: > modify_ldt has questionable locking and does not synchronize > threads. Improve it: redesign the locking and synchronize all > threads' LDTs using an IPI on all modifications. > > This will dramatically slow down modify_ldt in multithreaded > programs, but there shouldn't be any multithreaded programs that > care about modify_ldt's performance in the first place. > ... except 32-bit programs compiled with one specific version of glibc. Do we care? I don't think so.