Re: iommu=0 leading to panic when system defaults to using x2apic

[Keir Fraser <keir@xen.org>]

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@intel.com> 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@lists.xensource.com
> [mailto:xen-devel-bounces@lists.xensource.com] On Behalf Of Jan Beulich
> Sent: Friday, December 10, 2010 7:40 AM
> To: Zhang, Yang Z
> Cc: Keir Fraser; xen-devel@lists.xensource.com; 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@intel.com> 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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