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

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 16.01.17 at 16:15, <firemeteor@xxxxxxxxxxxxxxxxxxxxx> wrote:
> On Mon, Jan 16, 2017 at 9:56 PM, Jan Beulich <JBeulich@xxxxxxxx> wrote:
> 
>> >>> 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:
>> > 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.

Indeed.

>> > 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 don't understand - I'd normally assume the two to be the same
(with just different context made visible).

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

Nor do I understand this remark.

Jan


_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
https://lists.xen.org/xen-devel