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    SubjectRe: [PATCH 1/2] IOMMU Identity Mapping Support: iommu_identity_mapping definition
    On Thu, Jun 18, 2009 at 11:31:21AM -0700, Chris Wright wrote:

    > The 1-1 mapping is for all the host devices _not_ assigned to
    > guests. To eliminate the i/o overhead imposed on all guests not
    > using an assigned device or from i/o from host.
    > It's just the same as VT-d PassThrough mode for hardware that
    > doesn't support it.

    Ok, that makes sense. Thanks, Chris. However, that doesn't appear to
    be what the patch does---unless I'm misreading, if
    iommu_identity_mapping is set, *all* devices get identity
    mapping. Instead of a global command line option, we need to provide a
    way to enable/disable pt or identity mapping (I agree that the user
    shouldn't know or care which is used, the kernel should pick the best
    one automatically) on a per BDF basis.

    Muli Ben-Yehuda | | +972-4-8281080
    Manager, Virtualization and Systems Architecture
    Master Inventor, IBM Haifa Research Laboratory

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