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From: "Tian, Kevin" <kevin.tian@intel.com>
To: Lu Baolu <baolu.lu@linux.intel.com>, Joerg Roedel <joro@8bytes.org>, "Will
 Deacon" <will@kernel.org>, Robin Murphy <robin.murphy@arm.com>, "Jason
 Gunthorpe" <jgg@ziepe.ca>
CC: "Zhang, Tina" <tina.zhang@intel.com>, "Liu, Yi L" <yi.l.liu@intel.com>,
	"iommu@lists.linux.dev" <iommu@lists.linux.dev>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: RE: [PATCH 00/12] Consolidate domain cache invalidation
Thread-Topic: [PATCH 00/12] Consolidate domain cache invalidation
Thread-Index: AQHaflqt4JqYpqo6n0++IRRqba3zUrFMzouA
Date: Thu, 28 Mar 2024 07:59:37 +0000
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References: <20240325021705.249769-1-baolu.lu@linux.intel.com>
In-Reply-To: <20240325021705.249769-1-baolu.lu@linux.intel.com>
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> From: Lu Baolu <baolu.lu@linux.intel.com>
> Sent: Monday, March 25, 2024 10:17 AM
>=20
> 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:
>=20
> - IOMMU IOTLB Invalidation: This is done by iterating through the domain
>   IDs of each domain using the following code:
>=20
>         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);
>=20
>   This code could theoretically cause a use-after-free problem because
>   there's no lock to protect the "info" pointer within the loop.
>=20
> - 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.
>=20
> - 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?

>=20
> - 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.
>=20
> - Limited Debugging Support: There are currently no debugging aids
>   available for domain cache invalidation.
>=20
> By consolidating domain cache invalidation into a common location, we
> can address the issues mentioned above and improve the code's
> maintainability and debuggability.
>=20

overall this is a nice work!