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

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 16.01.17 at 14:43, <firemeteor@xxxxxxxxxxxxxxxxxxxxx> wrote:
> On Mon, Jan 16, 2017 at 8:37 PM, Jan Beulich <JBeulich@xxxxxxxx> wrote:
>> >>> On 16.01.17 at 10:25, <firemeteor@xxxxxxxxxxxxxxxxxxxxx> wrote:
>> > Here are some relevant logs, please help comment what's going on here and
>> > what's the next step of diagnose.
>> > It appears that the fault address 0xcfxxxxxx falls within the host RMRR
>> > region.
>>
>> Might be a problem in the RMRR setup itself, when the guest gets
>> the device assigned. But I'm not sure, as you've provided only
>> fragments of the log, instead of the full one (allowing to see in
>> which order the messages got logged). In any event the addresses
>> are, as you say, properly within the device's RMRR range.
>>
> Thanks for your quick reply, Jan.
> I meant to provide full log through third party service like pastebin but
> my network at work just get it blocked.
> Here it is: http://pastebin.com/RHVzhR6H 
> Note that the log here is before the fault issue shows up.

Well, it stopping before the first fault occurs makes it only
marginally bette than what you've provided so far.

> The fault log itself is really flooding. With a small 4MB ring buffer, I
> wasn't able to capture how it begins.

If you can't set up a serial console, grow the ring buffer.

> That RMRR setup has changed dramatically (from being basically
>> non-existent in the older versions), especially for USB devices (I
>> don't think I can conclude what type of device 0000:02:00.0 is).
>> There are messages logged with various failures in that process,
>> but some would be issued by debug hypervisors only. A good
>> first step (before possibly doing actual code instrumentation)
>> would therefore be to retry with a debug hypervisor, and post
>> the full log (huge amounts of trailing IOMMU fault messages may
>> of course be stripped as long as they're sufficiently similar, to
>> keep the overall log size manageable).
>>
> I can give it a try when I get some spare time.
> Could you show me the flow to build a debug hypervisor and the most
> relevant debug knobs to avoid log flooding?

For building a debug hypervisor, all you need to do is set
CONFIG_DEBUG=y in xen/.config. I don't think there are any
knobs to avoid log flooding - after all you've asked for the
verbosity via "iommu=verbose,debug".

Jan


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