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



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@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.

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



  -- Keir










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