Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751845AbcDUJac (ORCPT ); Thu, 21 Apr 2016 05:30:32 -0400 Received: from mail.kernel.org ([198.145.29.136]:42745 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750950AbcDUJa3 (ORCPT ); Thu, 21 Apr 2016 05:30:29 -0400 Date: Thu, 21 Apr 2016 10:30:13 +0100 (BST) From: Stefano Stabellini X-X-Sender: sstabellini@sstabellini-ThinkPad-X260 To: Juergen Gross cc: Stefano Stabellini , boris.ostrovsky@oracle.com, linux-kernel@vger.kernel.org, david.vrabel@citrix.com, xen-devel@lists.xenproject.org Subject: Re: [PATCH] xen/x86: actually allocate legacy interrupts on PV guests In-Reply-To: <57189880.6030102@suse.com> Message-ID: References: <57189880.6030102@suse.com> User-Agent: Alpine 2.10 (DEB 1266 2009-07-14) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2043 Lines: 53 On Thu, 21 Apr 2016, Juergen Gross wrote: > On 20/04/16 15:15, Stefano Stabellini wrote: > > 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. > > Would you mind describing the resulting problem? This is a good question. The symptom is: ata_piix: probe of 0000:00:01.1 failed with error -22 > With this commit message I'm absolutely not capable to decide whether > e.g. the other use of nr_legacy_irqs() in pci_xen_initial_domain() is > correct or not. I looked at it but I couldn't really test that code because if I try to change the number of ioapics in the system using the "noapic" command line option (which actually changes the number if ioapics, not lapics), I get an error from Linux saying that noapic is not supported when running on Xen. In my opinion having nr_legacy_irqs() calls in Xen code, which returns 0, is like playing with fire. I think it would be safer/saner to replace them all with NR_IRQS_LEGACY, simply because reading the code one would not expect that all those loops don't actually have any iterations. However I didn't make the change because I couldn't test it properly. > > Signed-off-by: Stefano Stabellini > > > > diff --git a/arch/x86/pci/xen.c b/arch/x86/pci/xen.c > > index beac4df..349b8ce 100644 > > --- a/arch/x86/pci/xen.c > > +++ b/arch/x86/pci/xen.c > > @@ -491,8 +491,11 @@ int __init pci_xen_initial_domain(void) > > #endif > > __acpi_register_gsi = acpi_register_gsi_xen; > > __acpi_unregister_gsi = NULL; > > - /* Pre-allocate legacy irqs */ > > - for (irq = 0; irq < nr_legacy_irqs(); irq++) { > > + /* > > + * Pre-allocate the legacy IRQs. Use NR_LEGACY_IRQS here > > + * because we don't have a PIC and thus nr_legacy_irqs() is zero. > > + */ > > + for (irq = 0; irq < NR_IRQS_LEGACY; irq++) { > > int trigger, polarity; > > > > if (acpi_get_override_irq(irq, &trigger, &polarity) == -1) > > >