Re: [Xen-devel] [PATCH v5 3/4] iommu: elide flushing for higher order map/unmap operations

[Paul Durrant <Paul.Durrant@xxxxxxxxxx>]

> -----Original Message-----
> From: Woods, Brian [mailto:Brian.Woods@xxxxxxx]
> Sent: 20 December 2018 19:27
> To: Paul Durrant <Paul.Durrant@xxxxxxxxxx>; xen-devel@xxxxxxxxxxxxxxxxxxxx
> Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>; Julien Grall
> <julien.grall@xxxxxxx>; Andrew Cooper <Andrew.Cooper3@xxxxxxxxxx>; George
> Dunlap <George.Dunlap@xxxxxxxxxx>; Ian Jackson <Ian.Jackson@xxxxxxxxxx>;
> Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>; Tim (Xen.org)
> <tim@xxxxxxx>; Wei Liu <wei.liu2@xxxxxxxxxx>; Suthikulpanit, Suravee
> <Suravee.Suthikulpanit@xxxxxxx>; Roger Pau Monne <roger.pau@xxxxxxxxxx>
> Subject: Re: [PATCH v5 3/4] iommu: elide flushing for higher order
> map/unmap operations
> 
> From: Paul Durrant <paul.durrant@xxxxxxxxxx>
> Sent: Monday, December 17, 2018 3:22 AM
> To: xen-devel@xxxxxxxxxxxxxxxxxxxx
> Cc: Paul Durrant; Stefano Stabellini; Julien Grall; Andrew Cooper; George
> Dunlap; Ian Jackson; Konrad Rzeszutek Wilk; Tim Deegan; Wei Liu;
> Suthikulpanit, Suravee; Woods, Brian; Roger Pau Monné
> Subject: [PATCH v5 3/4] iommu: elide flushing for higher order map/unmap
> operations
> 
> 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 semantics 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: Jan Beulich <jbeulich@xxxxxxxx>
> Reviewed-by: Kevin Tian <kevin.tian@xxxxxxxxx>
> 
> Acked-by: Brian Woods <brian.woods@xxxxxxx>

Thanks Brian,

  Paul

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