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Re: [Xen-devel] Unable to boot Xen 4.8 with iommu=0



On Fri, Feb 17, 2017 at 11:56 AM, Konrad Rzeszutek Wilk
<konrad.wilk@xxxxxxxxxx> wrote:
> . snip..
>> >> > Given this commit is pretty old, I'm also curious why it's only reported
>> >> > on 4.8. Tamas, did you succeed with iommu=0 pre 4.8, or 4.8 happens
>> >> > to be the one upon which you first tried iommu=0 on a platform 
>> >> > supporting
>> >> > interrupt remapping?
>> >>
>> >> It just happens to be the one I tried. VT-d was spamming my console
>> >> with faults like this:
>> >>
>> >> (XEN) [VT-D]DMAR:[DMA Write] Request device [0000:00:02.0] fault addr
>> >> 277e28000, iommu reg = ffff82c000201000
ffff82c000201000
>> >> (XEN) [VT-D]DMAR: reason 05 - PTE Write access is not set
>> >>
>> >> So I figured I can just turn it off to clean up my console. I still
>> >> don't know what these VT-d faults are about..
>> >
>> > What is the 0:02.0 device? Is it being passed in to your guest?
>>
>> Nope, there is no pass-through to any guests. The device is:
>>
>> 00:02.0 Display controller: Intel Corporation 2nd Generation Core
>> Processor Family Integrated Graphics Controller (rev 09)
>
> Let me guess, you have an SandyBridge motherboard and were using
> Intel AMT?

Correct.

>
> I see those all the time on that box (and I think my Haswell
> one too). The best I could narrow it down was that the card decided that
> certain area should be in the RMRR regions. With Venu/Elen's patch
> in (see 431685e8deb660976d8e986c41a647944e410c6c) you should be able
> to provide an rmrr paramater to include these addresses.

Some more information on how to use that flag would be valuable.. I
tried "rmrr=270000000-280000000=00:02.0" to no avail and I really have
no idea what I'm doing here =)

Tamas

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