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    SubjectRe: [RFC PATCH v1 2/8] iommu/arm-smmu-v3: Perform invalidations over installed_smmus
    On Mon, Aug 21, 2023 at 04:33:36PM +0800, Michael Shavit wrote:
    > > 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.

    You could also go in the direction of making a SVA BTM and SV non-BTM
    domain type and then you know what to do immediately in the notifier.

    > 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.

    Well, I would remove the duplication and add an argument if you intend
    to share the function that loops

    Jason

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