Re: [Xen-devel] [PATCH v4 3/4] iommu: elide flushing for higher order map/unmap operations

["Tian, Kevin" <kevin.tian@xxxxxxxxx>]

> From: Paul Durrant [mailto:paul.durrant@xxxxxxxxxx]
> Sent: Thursday, December 6, 2018 11:34 PM
> 
> This patch removes any implicit flushing that occurs in the implementation
> of map and unmap operations and adds new iommu_map/unmap()
> wrapper
> functions. To maintain sematics of the iommu_legacy_map/unmap()
> wrapper
> functions, these are modified to call the new wrapper functions and then
> perform an explicit flush operation.
> 
> Because VT-d currently performs two different types of flush dependent
> upon
> whether a PTE is being modified versus merely added (i.e. replacing a non-
> present PTE) 'iommu flush flags' are defined by this patch and the
> iommu_ops map_page() and unmap_page() methods are modified to OR
> the type
> of flush necessary for the PTE that has been populated or depopulated into
> an accumulated flags value. The accumulated value can then be passed into
> the explicit flush operation.
> 
> The ARM SMMU implementations of map_page() and unmap_page()
> currently
> perform no implicit flushing and therefore the modified methods do not
> adjust the flush flags.
> 
> NOTE: The per-cpu 'iommu_dont_flush_iotlb' is respected by the
>       iommu_legacy_map/unmap() wrapper functions and therefore this now
>       applies to all IOMMU implementations rather than just VT-d.
> 
> Signed-off-by: Paul Durrant <paul.durrant@xxxxxxxxxx>

Reviewed-by: Kevin Tian <kevin.tian@xxxxxxxxx>
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