RE: [Xen-devel] iommu=0 leading to panic when system defaults to using x2apic

["Kay, Allen M" <allen.m.kay@xxxxxxxxx>]

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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