From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754288Ab3A2Hrx (ORCPT ); Tue, 29 Jan 2013 02:47:53 -0500 Received: from mail-bk0-f44.google.com ([209.85.214.44]:36001 "EHLO mail-bk0-f44.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752717Ab3A2Hru (ORCPT ); Tue, 29 Jan 2013 02:47:50 -0500 Date: Tue, 29 Jan 2013 08:47:46 +0100 From: Ingo Molnar To: Yinghai Lu Cc: "Wang, Song-Bo (Stoney)" , "H. Peter Anvin" , Ingo Molnar , Thomas Gleixner , "Zhang, Lin-Bao (Linux Kernel R&D)" , "Pearson, Greg" , "linux-kernel@vger.kernel.org" , "suresh.b.siddha@intel.com" Subject: Re: [PATCH] x86/apic: check FADT settings after enable x2apic Message-ID: <20130129074746.GA594@gmail.com> References: <1358214636-4801-1-git-send-email-song-bo.wang@hp.com> <20130128101135.GD7168@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Yinghai Lu wrote: > On Mon, Jan 28, 2013 at 2:11 AM, Ingo Molnar wrote: > > > >> HP has systems that work with x2apic phys mode and BIOS set > >> ACPI_FADT_APIC_PHYSICAL in FADT table, and all cpuid < 255, > >> the spec requires BIOS only put system on xapic mode. Kernel > > > > Which spec? > > > >> will set to x2apic logical mode instead of x2apic phys mode. > > > > Which has exactly what bad effect on users of these systems? > > > > You left out the most important information from the changelog: > > why do users care, what good does the patch do? > > please check you are happy with this: > > --- > From: Stoney Wang > Subject: [PATCH] x86, apic: Check fadt x2apic phys in x2apic_phys_probe() > > HP has systems that only work with x2apic phys mode and BIOS set > ACPI_FADT_APIC_PHYSICAL in FADT table. But all apicid < 255, > according to x2apic-spec, chapter 2.9, BIOS need to pass the control > to the OS with xapic mode. > Kernel will set apic driver wrong to x2apic cluster instead of x2apic phys. > > The user will have to append nox2apic in boot command line to stay xapic mode, > or append x2apic_phys to switch to x2apic phys mode. This still does not explain what happens if none of this user action is taken. I.e. what exact _user visible problem_ does the patch fix? Is this really so unimportant to you? Almost everyone will start a changelog with explaining what badness happens. Not you - you explain everything from how the fix works to how to work around the bug - except describing the most important thing: theuser visible problem itself ... Weird. Thanks, Ingo