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

[Keir Fraser <keir@xen.org>]

On 14/12/2010 17:52, "Yinghai Lu" <yinghai@kernel.org> wrote:

> On 12/14/2010 09:08 AM, Jan Beulich wrote:
>>>>> On 14.12.10 at 17:53, "Kay, Allen M" <allen.m.kay@intel.com> wrote:
>>>>  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.
>> 
>> Oh, and I should have added that I'm currently polishing up
>> patches from Yinghai Lu to address this as well as other
>> problems preventing (certain?) large boxes from booting or
>> functioning correctly.
> 
> Yes, just want to make xen aligned to current Linux kernel behavior.
> BIOS guys said why Linux non-xen kernel is happy but xen kernel is not.
> 
> please check attached patches. Our big box with x2apic-preenabled, AND half
> cpus' apic id are above 255.
> 
> They are on top of xen-4.0.1. and first one is from Weidong in unstable.

I assume Jan is going to help with posting these as a regular patch series
for inclusion, with separate patches for 4.0 and 4.1 as appropriate.

 -- Keir

> Thanks
> 
> Yinghai Lu
>