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RE: [Xen-devel] iommu=0 leading to panic when system defaults to using x

To: Keir Fraser <keir@xxxxxxx>, Jan Beulich <JBeulich@xxxxxxxxxx>, "Zhang, Yang Z" <yang.z.zhang@xxxxxxxxx>
Subject: RE: [Xen-devel] iommu=0 leading to panic when system defaults to using x2apic
From: "Kay, Allen M" <allen.m.kay@xxxxxxxxx>
Date: Fri, 10 Dec 2010 16:07:46 -0800
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Thread-topic: [Xen-devel] iommu=0 leading to panic when system defaults to using x2apic
Yes, interrupt remapping is needed to be the intermediary between legacy 
IOxAPIC and MSI devices and the new x2APIC in the CPU. 

-----Original Message-----
From: Keir Fraser [mailto:keir.xen@xxxxxxxxx] On Behalf Of Keir Fraser
Sent: Friday, December 10, 2010 10:50 AM
To: Kay, Allen M; Jan Beulich; Zhang, Yang Z
Cc: xen-devel@xxxxxxxxxxxxxxxxxxx; Han, Weidong
Subject: Re: [Xen-devel] iommu=0 leading to panic when system defaults to using 
x2apic

Ah, and the interrupt remapping dependency is because PCI(e) devices cannot
address 32-bit APIC IDs?

 -- Keir

On 10/12/2010 18:26, "Kay, Allen M" <allen.m.kay@xxxxxxxxx> wrote:

> The architectural requirement is actually between interrupt remapping and
> x2apic.  Since interrupt remapping is part of the VT-d feature so current
> software requires all VT-d features enabled in order for x2apic to be enabled.
> 
> Strictly speaking DMA remapping is not required for x2apic.  However, queued
> invalidation is required since interrupt remapping requires queued
> invalidation.  So x2apic dependency is as follows:
> 
>     x2apic->interrupt remapping->queued invalidation
> 
> Due to historical reasons, the new VT-d features were built on top of the old
> ones as they become available.  Is there a requirement to separate this out?
> If so, we will need to re-design iommu boot parameter which took a while to
> get it right so most systems can now boot successfully.
> 
> Allen
> 
> -----Original Message-----
> From: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx
> [mailto:xen-devel-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of Jan Beulich
> Sent: Friday, December 10, 2010 7:40 AM
> To: Zhang, Yang Z
> Cc: Keir Fraser; xen-devel@xxxxxxxxxxxxxxxxxxx; Han, Weidong
> Subject: RE: [Xen-devel] iommu=0 leading to panic when system defaults to
> using x2apic
> 
>>>> On 10.12.10 at 16:00, "Zhang, Yang Z" <yang.z.zhang@xxxxxxxxx> wrote:
>> Yes, X2apic is depend on iommu. If disable iommu when using x2apic, it will
>> trigger the panic.
> 
> Would mind clarifying where this dependency actually is?
> 
> Thanks, Jan
> 
> 
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> Xen-devel@xxxxxxxxxxxxxxxxxxx
> http://lists.xensource.com/xen-devel



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