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    SubjectRe: [PATCH] intel-iommu: Default to non-coherent for domains unattached to iommus
    On Fri, Nov 11, 2011 at 4:37 PM, David Woodhouse <dwmw2@infradead.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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