Messages in this thread | | | Subject | Re: [PATCH] xen/x86: actually allocate legacy interrupts on PV guests | From | Juergen Gross <> | Date | Wed, 27 Apr 2016 07:02:11 +0200 |
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On 21/04/16 11:30, Stefano Stabellini wrote: > 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.
I'm quite sure you should change both uses of nr_legacy_irqs() in pci_xen_initial_domain().
Looking at xen_pcifront_enable_irq() I'm not really sure what is the correct thing to do.
Adding Konrad as he might have a better insight.
Juergen
> > However I didn't make the change because I couldn't test it properly. > > >>> Signed-off-by: Stefano Stabellini <sstabellini@kernel.org> >>> >>> 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) >>> >> > >
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