linux-kernel - RE: [PATCH v3 00/12] Consolidate domain cache invalidation

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Date: Tue, 23 Apr 2024 09:06:33 +0000
From: "Tian, Kevin" <kevin.tian@...el.com>
To: Lu Baolu <baolu.lu@...ux.intel.com>, Joerg Roedel <joro@...tes.org>, "Will
 Deacon" <will@...nel.org>, Robin Murphy <robin.murphy@....com>, "Jason
 Gunthorpe" <jgg@...pe.ca>
CC: "Zhang, Tina" <tina.zhang@...el.com>, "Liu, Yi L" <yi.l.liu@...el.com>,
	"iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH v3 00/12] Consolidate domain cache invalidation

> From: Lu Baolu <baolu.lu@...ux.intel.com>
> 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@...el.com>