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    SubjectRe: [RFC 3/3] mm: iommu: The Virtual Contiguous Memory Manager
    Daniel Walker wrote:
    > On Thu, 2010-07-01 at 15:00 -0700, Zach Pfeffer wrote:
    >
    >
    >> Additionally, the current IOMMU interface does not allow users to
    >> associate one page table with multiple IOMMUs unless the user explicitly
    >> wrote a muxed device underneith the IOMMU interface. This also could be
    >> done, but would have to be done for every such use case. Since the
    >> particular topology is run-time configurable all of these use-cases and
    >> more can be expressed without pushing the topology into the low-level
    >> IOMMU driver.
    >>
    >> The VCMM takes the long view. Its designed for a future in which the
    >> number of IOMMUs will go up and the ways in which these IOMMUs are
    >> composed will vary from system to system, and may vary at
    >> runtime. Already, there are ~20 different IOMMU map implementations in
    >> the kernel. Had the Linux kernel had the VCMM, many of those
    >> implementations could have leveraged the mapping and topology management
    >> of a VCMM, while focusing on a few key hardware specific functions (map
    >> this physical address, program the page table base register).
    >
    > So if we include this code which "map implementations" could you
    > collapse into this implementations ? Generally , what currently existing
    > code can VCMM help to eliminate?

    In theory, it can eliminate all code the interoperates between IOMMU,
    CPU and non-IOMMU based devices and all the mapping code, alignment,
    mapping attribute and special block size support that's been
    implemented.


    --
    Sent by an employee of the Qualcomm Innovation Center, Inc.
    The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.


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