Re: [PATCH v3 00/12] Consolidate domain cache invalidation

[Baolu Lu]

On 4/23/24 5:06 PM, Tian, Kevin wrote:
> > From: Lu Baolu<baolu.lu@xxxxxxxxxxxxxxx>
> > Sent: Tuesday, April 16, 2024 4:07 PM
> >
> > 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 a same IOMMU.
> >
> > - 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.
> There are several small nits but overall this series looks good to me:
>
> Reviewed-by: Kevin Tian<kevin.tian@xxxxxxxxx>

Thanks! I will queue this series to Joerg for wider verification.

Best regards,
baolu