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

[Wei Wang <wei.wang2@amd.com>]

On 09/02/2012 05:14 PM, Sander Eikelenboom wrote:
> Sunday, September 2, 2012, 4:58:58 PM, you wrote:
>
>> On 02/09/2012 09:43, "Sander Eikelenboom"<linux@eikelenboom.it>  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.
>
> OK, too bad!
> With xen 4.1 i haven't experienced those page faults, but a diff between /xen/drivers/passthrough/amd in both trees show quite some changes :(

Did you also update xen tools accordingly? Sometime I also saw a few 
IO_PAGE_FAULTs came from nic if my tools version and HV version did not 
match. But using recent 4.2 and corresponding xl, my tests went well.
BTW: You could also try iommu=no-sharept to see if it helps.

Thanks,
Wei

>>   -- Keir
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>>>>   -- Keir
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