Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752033AbaGFR2T (ORCPT ); Sun, 6 Jul 2014 13:28:19 -0400 Received: from mail-wi0-f170.google.com ([209.85.212.170]:41979 "EHLO mail-wi0-f170.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751881AbaGFR2P (ORCPT ); Sun, 6 Jul 2014 13:28:15 -0400 Date: Sun, 6 Jul 2014 20:28:05 +0300 From: Gleb Natapov To: Jan Kiszka Cc: Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , x86 , Linux Kernel Mailing List , kvm Subject: Re: [PATCH] x86: Make x2APIC support depend on interrupt remapping or guest support Message-ID: <20140706172805.GF4399@minantech.com> References: <53B7ADAA.9030101@web.de> <20140706151242.GN18167@minantech.com> <53B96A2B.4040909@web.de> <20140706154112.GO18167@minantech.com> <53B96FF5.2050107@web.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <53B96FF5.2050107@web.de> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, Jul 06, 2014 at 05:49:09PM +0200, Jan Kiszka wrote: > On 2014-07-06 17:41, Gleb Natapov wrote: > > On Sun, Jul 06, 2014 at 05:24:27PM +0200, Jan Kiszka wrote: > >> On 2014-07-06 17:12, Gleb Natapov wrote: > >>> On Sat, Jul 05, 2014 at 09:47:54AM +0200, Jan Kiszka wrote: > >>>> From: Jan Kiszka > >>>> > >>>> We are able to use x2APIC mode in the absence of interrupt remapping on > >>>> certain hypervisors. So it if fine to disable IRQ_REMAP without having > >>>> to give up x2APIC support. > >>> FWIW I did similar thing back when I added x2apic to KVM: > >>> http://linux.derkeiler.com/Mailing-Lists/Kernel/2009-06/msg14579.html > >>> But was advised against it. > >> > >> I don't get the point from that thread. > > It is not architectural to use x2apic without irq remapping, so Suresh > > Slightly off-topic for this patch: Is this dependency documented > somewhere? I guess there are broken systems where it can fail, but none > of the (Intel) boxes I tried so far had problems with x2APIC mode on > (given APIC IDs < 255) and IRQ remapping disabled. Not sure I saw that written, but I was told many times that this is so. -- Gleb. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/