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Re: [Xen-devel] IOMMU Interrupt Remapping query

To: Keir Fraser <keir.xen@xxxxxxxxx>
Subject: Re: [Xen-devel] IOMMU Interrupt Remapping query
From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Date: Tue, 7 Jun 2011 09:44:54 +0100
Cc: "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>, "Kay, Allen M" <allen.m.kay@xxxxxxxxx>
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On 06/06/11 19:53, Keir Fraser wrote:
> On 06/06/2011 17:37, "Andrew Cooper" <andrew.cooper3@xxxxxxxxxx> wrote:
>> On 06/06/11 16:21, Keir Fraser wrote:
>>> On 06/06/2011 15:32, "Andrew Cooper" <andrew.cooper3@xxxxxxxxxx> wrote:
>>>> This problem occurs with the XenServer version of 4.1.0 as well as on
>>>> xen-unstable at the moment.
>>>> Is there any hardware state which is not taken down by the disable
>>>> function, any subtle interactions which I have not taken account of?  I
>>>> have looked through the source and nothing pops out, but I am out of ideas.
>>>> Thanks in advance,
>> Attached are the two relevant patches, and two which I don't think are
>> relevant but might be if I am wrong.  crash_shutdown was an attempt to
>> make an iommu_ops which shut down all iommu functionality without saving
>> state.  debug-wip shows where I have put in debug statements.
> I think what you need to do ought to be quite similar to the teardown we do
> for S3 suspend. Have you considered reusing some of the mechanism in
> arch/x86/acpi/power.c? The function device_power_down(), and possibly some
> other bits in its caller, would be especially useful I should think. It
> already shuts down iommu functionality, turns off x2apic, etc etc. Even if
> it is not a perfect fit as is, perhaps it could be fixed up -- it sure looks
> similar to what ypu're trying to do. :-)
>  -- Keir
On a hunch, I tried that last night, and it resulted in the kdump kernel
hanging indefinitely (well - 14 hours now) on checking the hlt
instruction.  I will continue to play around with that area though, as
it does seem like a sensible idea.

>> kdump-fix-x2apic and apic-record-boot-mode are also in the source, but I
>> believe them to be unrelated to the current problem.
>> I have done some further debugging on the assumption that the order of
>> shutting down interupt remapping matters with shutting down the lapics
>> and ioapics, but disable_qinval causes a panic (qinval.c:222 - "queue
>> invalidate wait descriptor was not executed\n") if it is run before both
>> the lapics and ioapics are shut down.

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

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