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

["G.R." <firemeteor@xxxxxxxxxxxxxxxxxxxxx>]

On Mon, Jan 16, 2017 at 9:56 PM, Jan Beulich <JBeulich@xxxxxxxx> wrote:

>>> On 16.01.17 at 14:43, <firemeteor@users.sourceforge.net> wrote:
> On Mon, Jan 16, 2017 at 8:37 PM, Jan Beulich <JBeulich@xxxxxxxx> wrote:
>> >>> On 16.01.17 at 10:25, <firemeteor@users.sourceforge.net> wrote:
> 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.

Larger ring buffer seems to be the only option to me.
Seems that 'serial console' needs to be something physical.

 

> 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".

I assume I do not need to redo the ./configure here.

And I assume the xen/.config here refers to the root of the repos instead of the xen.git/xen subdirectory?

I couldn't find obvious debug knob in the gcc command-line, even though the build is with -O1.

 

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