Messages in this thread | | | Subject | Re: Xen regression, Was: [PATCH] x86/irq: Probe for PIC presence before allocating descs for legacy IRQs | From | David Vrabel <> | Date | Thu, 14 Apr 2016 14:45:22 +0100 |
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On 12/04/16 19:06, 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? If so, it doesn't work because it > doesn't get called for irq 14: > > 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 <sstabellini@kernel.org> > > 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)
I think I prefer this fix because PV guests don't have a legacy PIC and don't need any legacy irqs allocated so fiddling with nr_legacy_irqs() seems wrong.
But we do need a comment here saying something like:
/* * Pre-allocate the legacy IRQs. Use NR_LEGACY_IRQS here * because we don't have a PCI and thus nr_legacy_irqs() is zero. */
Does this make sense?
David
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