Re: [PATCH] intel-iommu: Default to non-coherent for domainsunattached to iommus

[Roland Dreier]

On Fri, Nov 11, 2011 at 5:08 PM, Chris Wright <chrisw@xxxxxxxxxxxx> wrote:
>> I would be more inclined to suspect that there's some
>> chipset buffering that we aren't correctly flushing (which might in
>> itself be a hardware issue, since the way to flush the cache is supposed
>> to be well-defined).
>
> Roland, have you tried switching BIOS to Coherency On and can do you
> ever see stale PTEs?

Yeah, the problems go away if I turn on coherency.

More details here:
  https://lkml.org/lkml/2011/10/11/412

(and after that email, I let the box run long enough that I'm pretty
sure turning VT-d coherency on does fix things)

I'd love to fix this but not sure how much I can contribute beyond
tests (I don't see anything wrong in the VT-d cache flushing code
in the kernel, and I did look for a while).

 - R.
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