Re: [PATCHv4] iommu/arm-smmu: Optimize ->tlb_flush_walk() for qcom implementation

[Robin Murphy]

On 2021-08-11 11:30, Will Deacon wrote:
> On Wed, Aug 11, 2021 at 11:37:25AM +0530, Sai Prakash Ranjan wrote:
> > diff --git a/drivers/iommu/arm/arm-smmu/arm-smmu.c b/drivers/iommu/arm/arm-smmu/arm-smmu.c
> > index f7da8953afbe..3904b598e0f9 100644
> > --- a/drivers/iommu/arm/arm-smmu/arm-smmu.c
> > +++ b/drivers/iommu/arm/arm-smmu/arm-smmu.c
> > @@ -327,9 +327,16 @@ static void arm_smmu_tlb_inv_range_s2(unsigned long iova, size_t size,
> >   static void arm_smmu_tlb_inv_walk_s1(unsigned long iova, size_t size,
> >   				     size_t granule, void *cookie)
> >   {
> > -	arm_smmu_tlb_inv_range_s1(iova, size, granule, cookie,
> > -				  ARM_SMMU_CB_S1_TLBIVA);
> > -	arm_smmu_tlb_sync_context(cookie);
> > +	struct arm_smmu_domain *smmu_domain = cookie;
> > +	struct arm_smmu_cfg *cfg = &smmu_domain->cfg;
> > +
> > +	if (cfg->flush_walk_prefer_tlbiasid) {
> > +		arm_smmu_tlb_inv_context_s1(cookie);
>
> Hmm, this introduces an unconditional wmb() if tlbiasid is preferred. I
> think that should be predicated on ARM_SMMU_FEAT_COHERENT_WALK like it is
> for the by-VA ops. Worth doing as a separate patch.
>
> > +	} else {
> > +		arm_smmu_tlb_inv_range_s1(iova, size, granule, cookie,
> > +					  ARM_SMMU_CB_S1_TLBIVA);
> > +		arm_smmu_tlb_sync_context(cookie);
> > +	}
> >   }
> >   
> >   static void arm_smmu_tlb_add_page_s1(struct iommu_iotlb_gather *gather,
> > @@ -765,8 +772,10 @@ static int arm_smmu_init_domain_context(struct iommu_domain *domain,
> >   		.iommu_dev	= smmu->dev,
> >   	};
> >   
> > -	if (!iommu_get_dma_strict(domain))
> > +	if (!iommu_get_dma_strict(domain)) {
> >   		pgtbl_cfg.quirks |= IO_PGTABLE_QUIRK_NON_STRICT;
> > +		cfg->flush_walk_prefer_tlbiasid = true;
>
> This is going to interact badly with Robin's series to allow dynamic
> transition to non-strict mode, as we don't have a mechanism to switch
> over to the by-ASID behaviour. Yes, it should _work_, but it's ugly having
> different TLBI behaviour just because of the how the domain became
> non-strict.
>
> Robin -- I think this originated from your idea at [1]. Any idea how to make
> it work with your other series, or shall we drop this part for now and leave
> the TLB invalidation behaviour the same for now?

Yeah, I'd say drop it - I'm currently half an hour into a first attempt 
at removing io_pgtable_tlb_flush_walk() entirely, which would make it 
moot for non-strict anyway.

Robin.