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

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

> And why is it that Xen panics when the BIOS pre-enabled x2apic
> mode without also enabling interrupt re-mapping, while Linux
> (afaict from looking at 2.6.32 code and output from an affected
> machine) simply enables interrupt re-mapping in this case?

AFAIK, Linux also requires interrupt remapping for x2apic.  I believe Weidong 
has fixed the panic issue in Xen when x2apic is enabled without enabling 
interrupt remapping.  It should now behave the same way as Linux.

Allen

-----Original Message-----
From: Jan Beulich [mailto:JBeulich@xxxxxxxxxx] 
Sent: Tuesday, December 14, 2010 12:22 AM
To: Kay, Allen M; Zhang, Yang Z
Cc: Han, Weidong; xen-devel@xxxxxxxxxxxxxxxxxxx; Keir Fraser
Subject: RE: [Xen-devel] iommu=0 leading to panic when system defaults to using 
x2apic

>>> On 10.12.10 at 19:26, "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.

And why is it that Xen panics when the BIOS pre-enabled x2apic
mode without also enabling interrupt re-mapping, while Linux
(afaict from looking at 2.6.32 code and output from an affected
machine) simply enables interrupt re-mapping in this case?

Thanks, Jan


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