From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932087Ab2LSQLR (ORCPT ); Wed, 19 Dec 2012 11:11:17 -0500 Received: from terminus.zytor.com ([198.137.202.10]:44234 "EHLO mail.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751387Ab2LSQLI (ORCPT ); Wed, 19 Dec 2012 11:11:08 -0500 Message-ID: <50D1E6ED.2070803@zytor.com> Date: Wed, 19 Dec 2012 08:10:21 -0800 From: "H. Peter Anvin" User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/17.0 Thunderbird/17.0 MIME-Version: 1.0 To: Yinghai Lu CC: "Zhang, Lin-Bao (Linux Kernel R&D)" , "linux-kernel@vger.kernel.org" , "alan@lxorguk.ukuu.org.uk" , "mingo@redhat.com" , "tglx@linutronix.de" , "x86@kernel.org" , "a.p.zijlstra@chello.nl" , "jarkko.sakkinen@intel.com" , "joerg.roedel@amd.com" , "agordeev@redhat.com" Subject: Re: Why Linux kernel forced to enter X2APIC mode( just because of booting cpu has supported x2apic) without depending on BIOS' setting in MSR->x2apic enablement bit ? References: <92645B27BF79D04FBD2B0F8494FFD0F91F1CAF@G1W3649.americas.hpqcorp.net> In-Reply-To: X-Enigmail-Version: 1.4.6 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 12/18/2012 09:49 AM, Yinghai Lu wrote: > > So you need to make cpuid show does not support x2apic --- check with > intel they have way to do that. > No, but there is a flag in ACPI that "this BIOS is broken with x2APIC". Setting that flag as opposed to fixing the bugs, though is very much not recommended, however; the lack of interrupt routing means there are ways for a rogue device to compromise the security provided by VT-d, see: http://www.invisiblethingslab.com/resources/2011/Software%20Attacks%20on%20Intel%20VT-d.pdf -hpa