From owner-freebsd-arch@FreeBSD.ORG Sun May 22 00:49:29 2005 Return-Path: <owner-freebsd-arch@FreeBSD.ORG> X-Original-To: freebsd-arch@freebsd.org Delivered-To: freebsd-arch@freebsd.org Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id 79B2816A41C for <freebsd-arch@freebsd.org>; Sun, 22 May 2005 00:49:29 +0000 (GMT) (envelope-from cperciva@freebsd.org) Received: from pd2mo2so.prod.shaw.ca (shawidc-mo1.cg.shawcable.net [24.71.223.10]) by mx1.FreeBSD.org (Postfix) with ESMTP id 2BEA843D1F for <freebsd-arch@freebsd.org>; Sun, 22 May 2005 00:49:28 +0000 (GMT) (envelope-from cperciva@freebsd.org) Received: from pd3mr3so.prod.shaw.ca (pd3mr3so-qfe3.prod.shaw.ca [10.0.141.179]) by l-daemon (Sun ONE Messaging Server 6.0 HotFix 1.01 (built Mar 15 2004)) with ESMTP id <0IGV00JDF8YGIIF0@l-daemon> for freebsd-arch@freebsd.org; Sat, 21 May 2005 18:49:28 -0600 (MDT) Received: from pn2ml7so.prod.shaw.ca ([10.0.121.151]) by pd3mr3so.prod.shaw.ca (Sun ONE Messaging Server 6.0 HotFix 1.01 (built Mar 15 2004)) with ESMTP id <0IGV0018R8YGV700@pd3mr3so.prod.shaw.ca> for freebsd-arch@freebsd.org; Sat, 21 May 2005 18:49:28 -0600 (MDT) Received: from [192.168.0.60] (S0106006067227a4a.vc.shawcable.net [24.87.209.6]) by l-daemon (iPlanet Messaging Server 5.2 HotFix 1.18 (built Jul 28 2003)) with ESMTP id <0IGV0029N8YFXX@l-daemon> for freebsd-arch@freebsd.org; Sat, 21 May 2005 18:49:28 -0600 (MDT) Date: Sat, 21 May 2005 17:49:20 -0700 From: Colin Percival <cperciva@freebsd.org> In-reply-to: <aef05e1ae6104223181ad3cf03e11390@xcllnt.net> To: Marcel Moolenaar <marcel@xcllnt.net> Message-id: <428FD710.4060200@freebsd.org> MIME-version: 1.0 Content-type: text/plain; charset=ISO-8859-1 Content-transfer-encoding: 7bit X-Accept-Language: en-us, en X-Enigmail-Version: 0.91.0.0 References: <428FC00B.3080909@freebsd.org> <aef05e1ae6104223181ad3cf03e11390@xcllnt.net> User-Agent: Mozilla Thunderbird 1.0.2 (X11/20050406) cc: freebsd-arch@freebsd.org Subject: Re: Scheduler fixes for hyperthreading X-BeenThere: freebsd-arch@freebsd.org X-Mailman-Version: 2.1.1 Precedence: list List-Id: Discussion related to FreeBSD architecture <freebsd-arch.freebsd.org> List-Unsubscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-arch>, <mailto:freebsd-arch-request@freebsd.org?subject=unsubscribe> List-Archive: <http://lists.freebsd.org/pipermail/freebsd-arch> List-Post: <mailto:freebsd-arch@freebsd.org> List-Help: <mailto:freebsd-arch-request@freebsd.org?subject=help> List-Subscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-arch>, <mailto:freebsd-arch-request@freebsd.org?subject=subscribe> X-List-Received-Date: Sun, 22 May 2005 00:49:29 -0000 Marcel Moolenaar wrote: > On May 21, 2005, at 4:11 PM, Colin Percival wrote: >> The following must be done before hyperthreading is re-enabled: >> [snip] > > Maybe it's a better idea to describe the problem in much more > detail, rather than dictate what you want someone else to do? > A pointer to where the problem is described/discussed would > do. The problem is described in my paper "Cache missing for fun and profit": http://www.daemonology.net/papers/htt.pdf Put simply, threads which share a processor core can monitor each others' memory access patterns, so we need to ensure that such co-scheduling never happens between threads which have different privileges. The reason I cut through to explaining what needed to be done is that I discussed this at length with several people from the FreeBSD security team before and during BSDCan; but these discussions were obviously not public, so I can't give a reference to them. Colin Percival