Re: [Xen-devel] Using debug-key 'o: Dump IOMMU p2m table, locks up machine

[Keir Fraser <keir.xen@xxxxxxxxx>]

On 02/09/2012 09:43, "Sander Eikelenboom" <linux@xxxxxxxxxxxxxx> wrote:

>> Quite simply, there likely needs to be more tracing on the IOMMU fault path.
>> That's a separate concern from your keyhandler of course, but just saying
>> I'd be looking for the former rather than the latter, for diagnosing
>> Sander's bug.
> 
> Are there any printk's I could add to get more relevant info about the AMD-Vi:
> IO_PAGE_FAULT ?

No really straightforward one. I think we need a per-IOMMU-type handler to
walk the IOMMU page table for a given virtual address, and dump every
page-table-entry on the path. Like an IOMMU version of show_page_walk().
Personally I would suspect this is more useful than the dump-everything
handlers: just give a *full* *detailed* walk for the actually interesting
virtual address (the one faulted on).

> I have attached new output from xl dmesg, this time with iommu=debug on (the
> option changed from 4.1 to 4.2).

Not easy to glean any more from that, without extra tracing such as
described above, and/or digging into the guest to find what driver-side
actions are causing the faults.

 -- Keir

> 
> 
>>  -- Keir
> 



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