Re: AMD IOMMU intremap tables and IOAPICs

[Andrew Cooper <andrew.cooper3@citrix.com>]

On 06/09/11 16:57, George Dunlap wrote:
> On Tue, Sep 6, 2011 at 4:54 PM, Andrew Cooper <andrew.cooper3@citrix.com> wrote:
>> 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".
> Hmm, so it sounds like enforcing non-sharing of vectors within a
> single IOAPIC is something we probably want to do even when we're not
> using an AMD IOMMU?
>
>  -George

Currently there is no code to disable auto EOI and do manual EOI
instead.  As a result, we should enforce non-sharing of vectors across
all IO-APICs.  It was on my irq cleanup list but seems to be a specific
problem for you at the moment.

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