Re: [Xen-devel] IOMMU fault with IGD passthrough setup on XEN 4.8.0

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 05.02.17 at 08:18, <firemeteor@xxxxxxxxxxxxxxxxxxxxx> wrote:
> On Sun, Feb 5, 2017 at 1:51 PM, G.R. <firemeteor@xxxxxxxxxxxxxxxxxxxxx> wrote:
>> On Fri, Jan 20, 2017 at 12:30 AM, Jan Beulich <JBeulich@xxxxxxxx> wrote:
>>>>>> On 17.01.17 at 16:08, <firemeteor@xxxxxxxxxxxxxxxxxxxxx> wrote:
>>>> But fortunately commenting out that line could still reproduce the IOMMU
>>>> fault.
>>>> I was lucky to capture the full log before it fills up my 100MB ring buffer
>>>> (in less than 2 seconds).
>>>
>>> So here's a first take at a debugging patch. I've tried to limit existing
>>> output, so that you'd have better chance of again capturing all
>>> interesting messages.
>>>
>>
>> Hi Jan,
>> I finally get some spare time to collect the debug info.
>> Please find the full log in the attachment.
>>
>> The mapping appears to be working:
>> (XEN) d8: RMRR [cf800,dfa00] mapped cf800
>> (XEN) d8: RMRR [cf800,dfa00] mapped cf900
>> (XEN) d8: RMRR [cf800,dfa00] mapped cfb00
>> (XEN) d8: RMRR [cf800,dfa00] mapped cff00
>> (XEN) d8: RMRR [cf800,dfa00] mapped d0700
>> (XEN) d8: RMRR [cf800,dfa00] mapped d1700
>> (XEN) d8: RMRR [cf800,dfa00] mapped d3700
>> (XEN) d8: RMRR [cf800,dfa00] mapped d7700
>> (XEN) d8: RMRR [cf800,dfa00] mapped df700
>> (XEN) d8: RMRR [cf800,dfa00] alloc -> ffff83013156ffb0
>>
>> But I'm not sure if the vtd_entries look correct: (Is the 'not
>> present' line okay?)

Rather not, hence ...

>> Still see the 'Fault overflow' line in the very first fault.
>> The fault is about write-access not permitted.

... this.

>> Is the map read-only here?

No, as you've noticed above, it's simply not present.

>> Or are we looking at the correct PTE?

Comparing the two dumps, I think we do.

> Attraching an xl dmesg log for dom0, which shows a more reasonable vtd_entry.
> Does it mean that the mapping wasn't properly setup in the domU case?

Looks like so.

> But we didn't see a map error in debug log either.

I'll have to look into this more closely.

Jan


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