Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753938AbcDMRgp (ORCPT ); Wed, 13 Apr 2016 13:36:45 -0400 Received: from aserp1040.oracle.com ([141.146.126.69]:27918 "EHLO aserp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751884AbcDMRgo (ORCPT ); Wed, 13 Apr 2016 13:36:44 -0400 Subject: Re: Xen regression, Was: [PATCH] x86/irq: Probe for PIC presence before allocating descs for legacy IRQs To: Stefano Stabellini References: <1446470676-1877-1-git-send-email-vkuznets@redhat.com> <570CF69A.1020701@oracle.com> <570D4645.20004@oracle.com> <570D69FE.6090200@oracle.com> <570D77D1.7080701@oracle.com> <570DA089.6060507@oracle.com> Cc: Vitaly Kuznetsov , x86@kernel.org, Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , Jiang Liu , "K. Y. Srinivasan" , linux-kernel@vger.kernel.org, konrad.wilk@oracle.com, david.vrabel@citrix.com, jgross@suse.com From: Boris Ostrovsky Message-ID: <570E838A.7000104@oracle.com> Date: Wed, 13 Apr 2016 13:36:10 -0400 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.1.0 MIME-Version: 1.0 In-Reply-To: <570DA089.6060507@oracle.com> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit X-Source-IP: userv0021.oracle.com [156.151.31.71] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1342 Lines: 32 On 04/12/2016 09:27 PM, Boris Ostrovsky wrote: > On 04/12/2016 07:15 PM, Stefano Stabellini wrote: >> On Tue, 12 Apr 2016, Boris Ostrovsky wrote: >>> On 04/12/2016 05:56 PM, Stefano Stabellini wrote: >>>> I am not sure, maybe you didn't have CONFIG_SPARSE_IRQ? >>>> But I am certain that 4.6-rc2, with the attached config, fails as Dom0 >>>> on QEMU with the following sequence of calls: >>> I did have CONFIG_SPARSE_IRQ and I just rebuilt 4.5.0 with your config >>> (4.6-rc3 doesn't build for me for some reason) and that booted dom0 >>> as well. >>> >>> BTW, what do you mean by "dom0 on QEMU"? >> I am running Xen and Linux inside a QEMU x86_64 emulated machine >> (nested >> virt). > > This I, of course, never tried. > > But given that things work in a single-level virt, doesn't this imply > that perhaps there is something in the emulation that's not quite right? OK, so this *is* broken on single level virt as well. It's just that we always end up using AHCI so lack of irq 14 (and 15) does not affect the system. And I guess in QEMU case it's IDE only, right? You patch does fix this but I wonder if we could change something in probe_8259A() so that we can continue using nr_legacy_irqs(). Using nr_legacy_irqs() and NR_IRQS_LEGACY at the same time is inconsistent and may cause us headaches in the future. -boris