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

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Message-ID: <CAL1RGDXZjKhA++3eFVPbazixaM7Q_JfBJyLKE0xjBs+sK55idg@mail.gmail.com>
Date:	Fri, 11 Nov 2011 16:46:45 -0800
From:	Roland Dreier <roland@...estorage.com>
To:	David Woodhouse <dwmw2@...radead.org>
Cc:	Alex Williamson <alex.williamson@...hat.com>,
	iommu@...ts.linux-foundation.org, linux-pci@...r.kernel.org,
	linux-kernel@...r.kernel.org, chrisw@...s-sol.org,
	ddutile@...hat.com
Subject: Re: [PATCH] intel-iommu: Default to non-coherent for domains
 unattached to iommus

On Fri, Nov 11, 2011 at 4:37 PM, David Woodhouse <dwmw2@...radead.org> wrote:
> This brain-damage only affects the first chipsets
> from before we worked out that cache incoherency was a *really* f*cking
> stupid idea, doesn't it?

As we talked about at KS, I have some Westmere EP (ie latest
and greatest server platform) systems where the BIOS exposes
an option that allows choosing VT-d coherency on or off, and
defaults it to "off".

What is the "official" Intel line on coherency with Westmere and
Tylersburg -- because as I also mentioned, I was seeing some
problems with VT-d and the default "coherency off" setting that
looked like the IOMMU HW is getting stale PTEs (ie a missing
or not working cache flush).

 - R.
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