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Re: [Xen-devel] XSA-36 / howto fix broken IVRS ACPI table

  • To: xen-devel@xxxxxxxxxxxxx
  • From: Hans Mueller <mcbeagle@xxxxxx>
  • Date: Wed, 24 Apr 2013 22:03:54 +0200
  • Delivery-date: Wed, 24 Apr 2013 20:04:50 +0000
  • List-id: Xen developer discussion <xen-devel.lists.xen.org>

On Wednesday, 24. April 2013 07:47:25 Jan Beulich wrote:
> >>> On 23.04.13 at 19:11, Hans Mueller <mcbeagle@xxxxxx> wrote:
> > However the problem seems not really to be fixed:
> > Interrupts generated within one domain can still harm other domains which
> > at least causes the kernel within these other domains to disable
> > interrupts.
> "The problem" being which problem? Even after looking back through
> the list archives, I haven't been able to spot a corresponding problem
> description. And if you resume a thread after several weeks without
> sufficiently quoting the original, it would be rather desirable for you
> to at least briefly summarize your original problem.

Perhaps it was unclear - better than 'the' problem might be 'a' problem - as 
briefly described regarding interrupts becoming disabled across domain borders.

However, I don't want to address that problem in this thread in detail, I just 
worry that the fixes applied to the BIOS are insufficient and want to check 
before starting a perhaps unnecessary discussion about the 'interrupt 

Since XSA-36 Xen disabled the I/O virtualisation because there was a 
conflicting IOAPIC entry within the IVRS table (probably for the disabled 
northbridge IOAPIC & using the handle/id for the enabled southbridge IOAPIC).
The manufacturer just removed this entry from the IVRS table which causes Xen 
to no longer complain about conflicting IOAPIC entries and enabling per-device 
vector maps.

So currently only the southbridge IOAPIC is enabled.

The question is whether the missing/disabled northbridge IOAPIC is a valid 
setup or might/will it raise any problems.

> The same physical IRQ being shared by multiple devices is entirely
> independent of XSA-36, and if your Dom0/DomU kernels can't cope
> with that they are what need fixing.
Is it obvious that such problems are not caused by the missing northbridge 
IOAPIC? I would then provide related details in a new thread.

Best Regards

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