linux-kernel - Re: [PATCH] intel-iommu: Default to non-coherent for domains unattached to iommus

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Message-ID: <CAL1RGDXiE5=GZvogdOnSkOKKc_YdWyrh0W+ZT2S71TmMdQHcBw@mail.gmail.com>
Date:	Fri, 11 Nov 2011 17:30:01 -0800
From:	Roland Dreier <roland@...estorage.com>
To:	Chris Wright <chrisw@...s-sol.org>
Cc:	David Woodhouse <dwmw2@...radead.org>,
	Alex Williamson <alex.williamson@...hat.com>,
	iommu@...ts.linux-foundation.org, linux-pci@...r.kernel.org,
	linux-kernel@...r.kernel.org, ddutile@...hat.com
Subject: Re: [PATCH] intel-iommu: Default to non-coherent for domains
 unattached to iommus

On Fri, Nov 11, 2011 at 5:08 PM, Chris Wright <chrisw@...s-sol.org> 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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