Messages in this thread | | | Subject | Re: [PATCHv2 1/3] iommu/io-pgtable: Add a quirk to use tlb_flush_all() for partial walk flush | From | Robin Murphy <> | Date | Tue, 22 Jun 2021 13:11:12 +0100 |
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On 2021-06-22 08:11, Sai Prakash Ranjan wrote: > Hi Robin, > > On 2021-06-21 21:15, Robin Murphy wrote: >> On 2021-06-18 03:51, Sai Prakash Ranjan wrote: >>> Add a quirk IO_PGTABLE_QUIRK_TLB_INV_ALL to invalidate entire context >>> with tlb_flush_all() callback in partial walk flush to improve unmap >>> performance on select few platforms where the cost of over-invalidation >>> is less than the unmap latency. >> >> I still think this doesn't belong anywhere near io-pgtable at all. >> It's a driver-internal decision how exactly it implements a non-leaf >> invalidation, and that may be more complex than a predetermined >> boolean decision. For example, I've just realised for SMMUv3 we can't >> invalidate multiple levels of table at once with a range command, >> since if we assume the whole thing is mapped at worst-case page >> granularity we may fail to invalidate any parts which are mapped as >> intermediate-level blocks. If invalidating a 1GB region (with 4KB >> granule) means having to fall back to 256K non-range commands, we may >> not want to invalidate by VA then, even though doing so for a 2MB >> region is still optimal. >> >> It's also quite feasible that drivers might want to do this for leaf >> invalidations too - if you don't like issuing 512 commands to >> invalidate 2MB, do you like issuing 511 commands to invalidate 2044KB? >> - and at that point the logic really has to be in the driver anyway. >> > > Ok I will move this to tlb_flush_walk() functions in the drivers. In the > previous > v1 thread, you suggested to make the choice in iommu_get_dma_strict() test, > I assume you meant the test in iommu_dma_init_domain() with a flag or > was it > the leaf driver(ex:arm-smmu.c) test of iommu_get_dma_strict() in > init_domain?
Yes, I meant literally inside the same condition where we currently set "pgtbl_cfg.quirks |= IO_PGTABLE_QUIRK_NON_STRICT;" in arm_smmu_init_domain_context().
> I am still a bit confused on where this flag would be? Should this be a > part > of struct iommu_domain?
Well, if you were to rewrite the config with an alternative set of flush_ops at that point it would be implicit. For a flag, probably either in arm_smmu_domain or arm_smmu_impl. Maybe a flag would be less useful than generalising straight to a "maximum number of by-VA invalidations it's worth sending individually" threshold value? It's clear to me what overall shape and separation of responsibility is most logical, but beyond that I don't have a particularly strong opinion on the exact implementation; I've just been chucking ideas around :)
Cheers, Robin.
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