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

[Roland Dreier]

On Fri, Nov 11, 2011 at 4:37 PM, David Woodhouse <dwmw2@xxxxxxxxxxxxx> 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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