From owner-freebsd-security@FreeBSD.ORG Mon Apr 24 21:43:28 2006 Return-Path: X-Original-To: freebsd-security@freebsd.org Delivered-To: freebsd-security@freebsd.org Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id 94DBD16A402; Mon, 24 Apr 2006 21:43:28 +0000 (UTC) (envelope-from stb@lassitu.de) Received: from koef.zs64.net (koef.zs64.net [213.238.47.30]) by mx1.FreeBSD.org (Postfix) with ESMTP id 6E22343D49; Mon, 24 Apr 2006 21:43:27 +0000 (GMT) (envelope-from stb@lassitu.de) Received: (from stb@koef.zs64.net) (authenticated) by koef.zs64.net (8.13.6/8.13.4) with ESMTP id k3OLhExH000456 (version=TLSv1/SSLv3 cipher=RC4-SHA bits=128 verify=NO); Mon, 24 Apr 2006 23:43:25 +0200 (CEST) (envelope-from stb@lassitu.de) In-Reply-To: <200604242117.k3OLH2RG032117@repoman.freebsd.org> References: <200604242117.k3OLH2RG032117@repoman.freebsd.org> Mime-Version: 1.0 (Apple Message framework v749.3) Content-Type: text/plain; charset=US-ASCII; delsp=yes; format=flowed Message-Id: <662E8E58-F87F-4098-B573-06A863B72B7B@lassitu.de> Content-Transfer-Encoding: 7bit From: Stefan Bethke Date: Mon, 24 Apr 2006 23:43:13 +0200 To: Colin Percival X-Mailer: Apple Mail (2.749.3) Cc: freebsd-security@freebsd.org Subject: Re: cvs commit: src/sys/amd64/amd64 mp_machdep.c src/sys/i386/i386 mp_machdep.c X-BeenThere: freebsd-security@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: "Security issues \[members-only posting\]" List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 24 Apr 2006 21:43:28 -0000 Am 24.04.2006 um 23:17 schrieb Colin Percival: > cperciva 2006-04-24 21:17:02 UTC > > FreeBSD src repository > > Modified files: > sys/amd64/amd64 mp_machdep.c > sys/i386/i386 mp_machdep.c > Log: > Adjust dangerous-shared-cache-detection logic from "all shared data > caches are dangerous" to "a shared L1 data cache is dangerous". > This > is a compromise between paranoia and performance: Unlike the L1 > cache, > nobody has publicly demonstrated a cryptographic side channel which > exploits the L2 cache -- this is harder due to the larger size, > lower > bandwidth, and greater associativity -- and prohibiting shared L2 > caches turns Intel Core Duo processors into Intel Core Solo > processors. > > As before, the 'machdep.hyperthreading_allowed' sysctl will allow > even > the L1 data cache to be shared. I do not pretend to understand the background, but from your description it sounds like performance on Core Duo machines will be bad unless this change is made, or the potentially dangerous sysctl is active. If that is indeed the case, will this change make it into 6.1? Thanks, Stefan -- Stefan Bethke Fon +49 170 346 0140