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    SubjectRe: [PATCH] intel-iommu: Default to non-coherent for domains unattached to iommus
    On Fri, 2011-11-11 at 16:45 -0800, Chris Wright wrote:
    > > So if you were to ditch the whole idea of a per-domain runtime update,
    > > and instead calculate a global value for 'iommu_coherency' at boot time,
    > > by iterating over for_each_active_iommu()¹, I think that would be a
    > > better way to deal with the issue. And you *could* really call that a
    > > 'fix'.
    > >
    > > Make sense?
    > Ideally, yes. Not sure we can practically do it though. Would have to
    > be sure we force incoherent access mode for the busted hw.

    Why's it not practical? You do the *same* loop we currently have in
    domain_update_iommu_coherency(), except that you do it just *once*, over
    all active IOMMUs, at boot time. And then you just use that result
    forever more.

    So if *any* IOMMU in the system is non-coherent, you run them all that

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