Messages in this thread | | | From | Michael Shavit <> | Date | Mon, 21 Aug 2023 16:33:36 +0800 | Subject | Re: [RFC PATCH v1 2/8] iommu/arm-smmu-v3: Perform invalidations over installed_smmus |
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On Fri, Aug 18, 2023 at 9:51 PM Jason Gunthorpe <jgg@nvidia.com> wrote: > > On Fri, Aug 18, 2023 at 11:44:55AM +0800, Michael Shavit wrote: > > On Fri, Aug 18, 2023 at 3:41 AM Robin Murphy <robin.murphy@arm.com> wrote: > > > > > > On 2023-08-17 20:20, Jason Gunthorpe wrote: > > > > It is certainly wrong to skip invalidations generated for any other > > > > reason. > > > > > > > > From what I can tell SVA domains should have their CD table entry > > > > programmed with "ASET=0" and normal paging domains should be > > > > programmed with "ASET=1". This causes only the SVA domains to listen > > > > to the BTM invalidations. > > > > > > Correct. > > > > > > Thanks, > > > Robin. > > > > Would it be fair to rename arm_smmu_tlb_inv_asid (or move into > > arm-smmu-v3-sva) to make it explicit that it shouldn't be used outside > > of SVA then? Or add a parameter such as skip_btm_capable_devices. > > ??? > > arm_smmu_tlb_inv_asid() is generally used in many places and has > nothing to do with BTM.. > > Did you mean arm_smmu_tlb_inv_range_asid ?
Whoops yes that's what I meant.
> > Broadly, invalidation is not SVA specific.. > > Notice that arm_smmu_tlb_inv_range_asid() already duplicates > arm_smmu_tlb_inv_range_domain(). > > IMHO I would split the ATC step out of arm_smmu_mm_invalidate_range(), > get rid of arm_smmu_tlb_inv_range_domain(), and have the mmu notifier > just do as it already does: > > if (!(smmu_domain->smmu->features & ARM_SMMU_FEAT_BTM)) > arm_smmu_tlb_inv_range_domain_no_atc(start, size, smmu_mn->cd->asid, > PAGE_SIZE, false, smmu_domain); > arm_smmu_atc_inv_domain(smmu_domain, start, size); > > And make arm_smmu_tlb_inv_range_domain() just call > arm_smmu_tlb_inv_range_domain_no_atc(); > arm_smmu_atc_inv_domain();
That's a nice clean-up but doesn't really solve the problem faced by this patch.
This patch series eliminates the smmu_domain->smmu handle, replacing it for a list of SMMUs. So SVA can no longer optimize the arm_smmu_tlb_inv_range_asid call away by checking whether the SMMU BTM feature is enabled since there's now a list of SMMUs with possibly heterogeneous support for the feature. Since there's now a loop over a series of SMMUs inside arm_smmu_tlb_inv_range_asid, it makes sense to move the check into that loop. This technically works because only SVA is calling arm_smmu_tlb_inv_range_asid but can (IMO) risk introducing bugs in the future since it's not obvious from the function name.
The suggestion was then to introduce a parameter to arm_smmu_tlb_inv_range_asid (or arm_smmu_tlb_inv_range_domain_no_atc) to make this behavior explicit in the API.
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