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

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Date: Wed, 24 Apr 2024 10:46:06 +0800
From: Baolu Lu <baolu.lu@...ux.intel.com>
To: "Tian, Kevin" <kevin.tian@...el.com>, Joerg Roedel <joro@...tes.org>,
 Will Deacon <will@...nel.org>, Robin Murphy <robin.murphy@....com>,
 Jason Gunthorpe <jgg@...pe.ca>
Cc: baolu.lu@...ux.intel.com, "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

On 4/23/24 5:06 PM, Tian, Kevin wrote:
>> 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>

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

Best regards,
baolu