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    SubjectRe: [PATCH kernel v11 23/34] powerpc/iommu/powernv: Release replaced TCE
    On Fri, May 29, 2015 at 06:44:47PM +1000, Alexey Kardashevskiy wrote:
    > At the moment writing new TCE value to the IOMMU table fails with EBUSY
    > if there is a valid entry already. However PAPR specification allows
    > the guest to write new TCE value without clearing it first.
    >
    > Another problem this patch is addressing is the use of pool locks for
    > external IOMMU users such as VFIO. The pool locks are to protect
    > DMA page allocator rather than entries and since the host kernel does
    > not control what pages are in use, there is no point in pool locks and
    > exchange()+put_page(oldtce) is sufficient to avoid possible races.
    >
    > This adds an exchange() callback to iommu_table_ops which does the same
    > thing as set() plus it returns replaced TCE and DMA direction so
    > the caller can release the pages afterwards. The exchange() receives
    > a physical address unlike set() which receives linear mapping address;
    > and returns a physical address as the clear() does.
    >
    > This implements exchange() for P5IOC2/IODA/IODA2. This adds a requirement
    > for a platform to have exchange() implemented in order to support VFIO.
    >
    > This replaces iommu_tce_build() and iommu_clear_tce() with
    > a single iommu_tce_xchg().
    >
    > This makes sure that TCE permission bits are not set in TCE passed to
    > IOMMU API as those are to be calculated by platform code from
    > DMA direction.
    >
    > This moves SetPageDirty() to the IOMMU code to make it work for both
    > VFIO ioctl interface in in-kernel TCE acceleration (when it becomes
    > available later).
    >
    > Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
    > [aw: for the vfio related changes]
    > Acked-by: Alex Williamson <alex.williamson@redhat.com>

    Reviewed-by: David Gibson <david@gibson.dropbear.id.au>

    --
    David Gibson | I'll have my music baroque, and my code
    david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_
    | _way_ _around_!
    http://www.ozlabs.org/~dgibson
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