From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753022Ab1EKPhq (ORCPT ); Wed, 11 May 2011 11:37:46 -0400 Received: from mga11.intel.com ([192.55.52.93]:21107 "EHLO mga11.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751719Ab1EKPho (ORCPT ); Wed, 11 May 2011 11:37:44 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.64,353,1301900400"; d="scan'208";a="925346" Date: Wed, 11 May 2011 23:39:23 -0400 From: Youquan Song To: "Woodhouse, David" Cc: "Song, Youquan" , "linux-kernel@vger.kernel.org" , "akpm@linux-foundation.org" , "mingo@elte.hu" , "tglx@linutronix.de" , "hpa@zytor.com" , "hpa@linux.intel.com" , "Kay, Allen M" , "Siddha, Suresh B" , "Liu, Kent" , Youquan Song , rajesh.sankaran@intel.com, asit.k.mallick@intel.com Subject: Re: [PATCH v2] x86, vt-d: enable x2apic opt out Message-ID: <20110512033923.GA19708@linux-youquan.bj.intel.com> References: <1302764783-24491-1-git-send-email-youquan.song@intel.com> <1305126431.30435.163.camel@i7.infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1305126431.30435.163.camel@i7.infradead.org> User-Agent: Mutt/1.5.17 (2007-11-01) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > Given that x2apic is *required* to be safe from irq injection tricks, > why would we ever want to manually disable it? > Is this just a workaround for a crappy BIOS? What is the *actual* reason > for wanting to disable x2apic? The VT-d 1.3 version specification add this new feature because OEM request it. If OEM platform has issues to support x2apic or BIOS is buggy to support x2apic, there is alternative way to opt out x2apic. Refer to VT-d 1.3 specification Chpater 8.1. Thanks -Youquan