RE: [PATCH 00/12] Consolidate domain cache invalidation

[Tian, Kevin]

> From: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
> Sent: Monday, March 25, 2024 10:17 AM
> 
> The IOMMU hardware cache needs to be invalidated whenever the
> mappings
> in the domain are changed. Currently, domain cache invalidation is
> scattered across different places, causing several issues:
> 
> - IOMMU IOTLB Invalidation: This is done by iterating through the domain
>   IDs of each domain using the following code:
> 
>         xa_for_each(&dmar_domain->iommu_array, i, info)
>                 iommu_flush_iotlb_psi(info->iommu, dmar_domain,
>                                       start_pfn, nrpages,
>                                       list_empty(&gather->freelist), 0);
> 
>   This code could theoretically cause a use-after-free problem because
>   there's no lock to protect the "info" pointer within the loop.
> 
> - Inconsistent Invalidation Methods: Different domain types implement
>   their own cache invalidation methods, making the code difficult to
>   maintain. For example, the DMA domain, SVA domain, and nested domain
>   have similar cache invalidation code scattered across different files.
> 
> - SVA Domain Inconsistency: The SVA domain implementation uses a
>   completely different data structure to track attached devices compared
>   to other domains. This creates unnecessary differences and, even
>   worse, leads to duplicate IOTLB invalidation when an SVA domain is
>   attached to devices belonging to different IOMMU domains.

can you elaborate how duplicated invalidations are caused?

> 
> - Nested Domain Dependency: The special overlap between a nested domain
>   and its parent domain requires a dedicated parent_domain_flush()
>   helper function to be called everywhere the parent domain's mapping
>   changes.
> 
> - Limited Debugging Support: There are currently no debugging aids
>   available for domain cache invalidation.
> 
> By consolidating domain cache invalidation into a common location, we
> can address the issues mentioned above and improve the code's
> maintainability and debuggability.
> 

overall this is a nice work!