Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S965375AbcDLTDw (ORCPT ); Tue, 12 Apr 2016 15:03:52 -0400 Received: from aserp1040.oracle.com ([141.146.126.69]:21773 "EHLO aserp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S965051AbcDLTDv (ORCPT ); Tue, 12 Apr 2016 15:03:51 -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> 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: <570D4645.20004@oracle.com> Date: Tue, 12 Apr 2016 15:02:29 -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: Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit X-Source-IP: aserv0021.oracle.com [141.146.126.233] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2550 Lines: 75 On 04/12/2016 02:06 PM, Stefano Stabellini wrote: > On Tue, 12 Apr 2016, Boris Ostrovsky wrote: >> On 04/11/2016 10:08 PM, Stefano Stabellini wrote: >>> Hi all, >>> >>> Unfortunately this patch (now commit >>> 8c058b0b9c34d8c8d7912880956543769323e2d8) causes a regression on Xen >>> when running on top of QEMU: the number of PIT irqs get set to 0 by >>> probe_8259A but actually there are 16. >>> >>> Any suggestions on how to fix this? >>> >>> 1) we could revert 8c058b0b9c34d8c8d7912880956543769323e2d8 >>> 2) we could introduce an 'if (!xen_domain())' in probe_8259A >>> 3) suggestions welcome >> Stefano, do you have b4ff8389ed14b849354b59ce9b360bdefcdbf99c ? >> >> It was supposed to fix this problem for Xen. However, I just noticed that >> arch/arm64/include/asm/irq.h makes nr_legacy_irqs() return 0 (unlike >> arch/arm/include/asm/irq.h). Could that be the problem? > I have b4ff8389ed14b849354b59ce9b360bdefcdbf99c but it doesn't fix the > issue for me. > > Is the idea of your patch that xen_allocate_irq_gsi will allocate the > descriptor dynamically instead? Right. > If so, it doesn't work because it > doesn't get called for irq 14: So how has it worked until now then? > > piix_init_one -> ata_pci_sff_activate_host -> devm_request_irq -> > devm_request_threaded_irq-> request_threaded_irq -> irq_to_desc(14) -> > -EVAIL > > If you look at pci_xen_initial_domain, the loop: > > for (irq = 0; irq < nr_legacy_irqs(); irq++) { > > won't work anymore because by the time is called, nr_legacy_irqs() > already returns 0, because it has been changed by probe_8259A(). > > We also need the following patch: > > --- > > xen/x86: actually allocate legacy interrupts on PV guests > > b4ff8389ed14 is incomplete: relies on nr_legacy_irqs() to get the number > of legacy interrupts when actually nr_legacy_irqs() returns 0 after > probe_8259A(). Use NR_IRQS_LEGACY instead. > > Signed-off-by: Stefano Stabellini > > diff --git a/arch/x86/pci/xen.c b/arch/x86/pci/xen.c > index beac4df..6db0060 100644 > --- a/arch/x86/pci/xen.c > +++ b/arch/x86/pci/xen.c > @@ -492,7 +492,7 @@ int __init pci_xen_initial_domain(void) > __acpi_register_gsi = acpi_register_gsi_xen; > __acpi_unregister_gsi = NULL; > /* Pre-allocate legacy irqs */ > - for (irq = 0; irq < nr_legacy_irqs(); irq++) { > + for (irq = 0; irq < NR_IRQS_LEGACY; irq++) { > int trigger, polarity; > > if (acpi_get_override_irq(irq, &trigger, &polarity) == -1) Won't we need the same change in the 'if (0 == nr_ioapics)' clause? -boris