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Re: [PATCH] xen/x86: actually allocate legacy interrupts on PV guests

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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 <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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[PATCH] xen/x86: actually allocate legacy interrupts on PV guests Stefano Stabellini <sstabellini@kernel.org> - 2016-04-20 15:20 +0200
  Re: [PATCH] xen/x86: actually allocate legacy interrupts on PV guests Juergen Gross <jgross@suse.com> - 2016-04-21 11:10 +0200
    Re: [PATCH] xen/x86: actually allocate legacy interrupts on PV  guests Stefano Stabellini <sstabellini@kernel.org> - 2016-04-21 11:40 +0200
      Re: [PATCH] xen/x86: actually allocate legacy interrupts on PV guests Juergen Gross <jgross@suse.com> - 2016-04-27 07:10 +0200
        Re: [Xen-devel] [PATCH] xen/x86: actually allocate legacy interrupts  on PV guests David Vrabel <david.vrabel@citrix.com> - 2016-04-27 11:40 +0200
          Re: [Xen-devel] [PATCH] xen/x86: actually allocate legacy interrupts  on PV guests Boris Ostrovsky <boris.ostrovsky@oracle.com> - 2016-04-27 15:40 +0200
            Re: [Xen-devel] [PATCH] xen/x86: actually allocate legacy interrupts  on PV guests David Vrabel <david.vrabel@citrix.com> - 2016-04-27 15:50 +0200
              Re: [Xen-devel] [PATCH] xen/x86: actually allocate legacy interrupts  on PV guests Boris Ostrovsky <boris.ostrovsky@oracle.com> - 2016-04-27 16:10 +0200
  Re: [Xen-devel] [PATCH] xen/x86: actually allocate legacy interrupts  on PV guests Olaf Hering <olaf@aepfle.de> - 2016-04-21 13:10 +0200

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