Re: [Xen-devel] AMD IOMMU intremap tables and IOAPICs

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 06/09/11 16:47, George Dunlap wrote:
> Wei,
>
> Quick question:  Am I reading the code correctly, that even with
> per-device interrupt remap tables, that GSIs are accounted to the
> intremap table of the corresponding IOAPIC, presumably because the
> IOMMU sees interrupts generated as GSIs as coming from the IOAPIC?  In
> that case, then we need all devices sharing the same IOAPIC must not
> have any vector collisions.  Is that correct?

Based on the ICH10 IO-APIC documentation with respect to auto EOIs, we
cant have any two IRQs across any IO-APICs sharing a vector,
irrespective of IOMMU or not.  (Because the EOI'ing an IO-APIC entry
only takes account of vector and not destination)

If we were to disable the auto EOI broadcast and do manual EOI'ing (only
available on newer versions of the local apic) then we could reduce that
restriction to "no two IRQs in the same IO-APIC may share a vector".

~Andrew

>  -George
>
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-- 
Andrew Cooper - Dom0 Kernel Engineer, Citrix XenServer
T: +44 (0)1223 225 900, http://www.citrix.com


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