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Re: [Xen-devel] [PATCH v13 1/4] remove late (on-demand) construction of IOMMU page tables

On Wed, Sep 18, 2019 at 11:41:10AM +0100, Paul Durrant wrote:
> Now that there is a per-domain IOMMU-enable flag, which should be set if
> any device is going to be passed through, stop deferring page table
> construction until the assignment is done. Also don't tear down the tables
> again when the last device is de-assigned; defer that task until domain
> destruction.
> This allows the has_iommu_pt() helper and iommu_status enumeration to be
> removed. Calls to has_iommu_pt() are simply replaced by calls to
> is_iommu_enabled(). Remaining open-coded tests of iommu_hap_pt_share can
> also be replaced by calls to iommu_use_hap_pt().
> The arch_iommu_populate_page_table() and iommu_construct() functions become
> redundant, as does the 'strict mode' dom0 page_list mapping code in
> iommu_hwdom_init(), and iommu_teardown() can be made static is its only
> remaining caller, iommu_domain_destroy(), is within the same source
> module.
> All in all, about 220 lines of code are removed from the hypervisor (at
> the expense of some additions in the toolstack).
> NOTE: This patch will cause a small amount of extra resource to be used
>       to accommodate IOMMU page tables that may never be used, since the
>       per-domain IOMMU-enable flag is currently set to the value of the
>       global iommu_enable flag. A subsequent patch will add an option to
>       the toolstack to allow it to be turned off if there is no intention
>       to assign passthrough hardware to the domain.
>       To account for the extra resource, 'iommu_memkb' has been added to
>       domain_build_info. This patch sets it to a value calculated based
>       on the domain's maximum memory when the P2M sharing is either not
>       supported or globally disabled, or zero otherwise. However, when
>       the toolstack option mentioned above is added, it will also be zero
>       if the per-domain IOMMU-enable flag is turned off.
> Signed-off-by: Paul Durrant <paul.durrant@xxxxxxxxxx>
> Reviewed-by: Alexandru Isaila <aisaila@xxxxxxxxxxxxxxx>
> Acked-by: Razvan Cojocaru <rcojocaru@xxxxxxxxxxxxxxx>
> Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
> Acked-by: Julien Grall <julien.grall@xxxxxxx>

Acked-by: Wei Liu <wl@xxxxxxx>

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