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    SubjectRe: [PATCH 1/2] IOMMU Identity Mapping Support: iommu_identity_mapping definition
    On Thu, Jun 18, 2009 at 11:14:51AM -0700, Yu, Fenghua wrote:
    > >
    > >On Thu, Jun 18, 2009 at 11:05:14AM -0700, Fenghua Yu wrote:
    > >
    > >> IOMMU Identity Mapping Support: iommu_identity_mapping definition
    > >>
    > >> Identity mapping for IOMMU defines a single domain to 1:1 map all
    > >> pci devices to all usable memory.
    > >
    > >Why use VT-d at all in this case? Do you have a use-case in mind?
    >
    > Some users want to use VT-d in KVM but are concerned of DMA
    > remapping performance. They can use identity mapping and still have
    > KVM on VT-d. They can also use pass through patch (sent out before)
    > if hardware supports pass through.

    Sorry, I must be missing something. For the normal device assignment
    case, we want the IOMMU page tables to have gpa->hpa mappings rather
    than the 1-1 identity mapping. How do you envision the 1-1 mapping
    being used in the device assignment case?

    Cheers,
    Muli
    --
    Muli Ben-Yehuda | muli@il.ibm.com | +972-4-8281080
    Manager, Virtualization and Systems Architecture
    Master Inventor, IBM Haifa Research Laboratory


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