Messages in this thread | | | Date | Mon, 8 Apr 2024 11:05:35 +0800 | Subject | Re: [PATCH 00/12] Consolidate domain cache invalidation | From | Baolu Lu <> |
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On 4/8/24 11:03 AM, Tian, Kevin wrote: >> From: Baolu Lu <baolu.lu@linux.intel.com> >> Sent: Sunday, April 7, 2024 3:28 PM >> >> On 3/28/24 3:59 PM, Tian, Kevin wrote: >>>> From: Lu Baolu<baolu.lu@linux.intel.com> >>>> 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? >> >> Yes, sure. >> >> Current Intel SVA implementation keeps the bond between mm and a PASID >> of a device in a list of intel_svm_dev. In the mm notifier callback, it >> iterates all intel_svam_dev in the list and invalidates the IOTLB and >> device TLB sequentially. >> >> If multiple devices belong to a single IOMMU, the IOTLB will be flushed >> multiple times. However, since these devices share the same domain ID >> and PASID, a single IOTLB cache invalidation is sufficient. The >> additional flushes are redundant and negatively impact performance. >> > > yes it's redundant. But what does "devices belonging to different > IOMMU domains" in the original context try to convey? From above > explanation it sounds irrelevant...
My typo. :-) Sorry for the confusion.
I should say,
"... attached to devices belonging to a same IOMMU ..."
Best regards, baolu
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