linux-kernel - Re: [PATCHv4] iommu/arm-smmu: Optimize ->tlb_flush

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Date:   Wed, 11 Aug 2021 16:23:16 +0530
From:   Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>
To:     Will Deacon <will@...nel.org>
Cc:     Robin Murphy <robin.murphy@....com>,
        Joerg Roedel <joro@...tes.org>,
        iommu@...ts.linux-foundation.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-arm-msm@...r.kernel.org,
        Doug Anderson <dianders@...omium.org>,
        Krishna Reddy <vdumpa@...dia.com>,
        Thierry Reding <treding@...dia.com>,
        Tomasz Figa <tfiga@...omium.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>
Subject: Re: [PATCHv4] iommu/arm-smmu: Optimize ->tlb_flush_walk() for qcom
 implementation


On 2021-08-11 16:00, 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.
> 

Ok I will keep this as-is for now then.

>> +	} 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?
> 
> Will
> 
> [1] 
> https://lore.kernel.org/r/da62ff1c-9b49-34d3-69a1-1a674e4a30f7@arm.com

Right, I think we can drop this non-strict change for now because it 
also makes
it a pain to backport it to 5.4/5.10 kernels because of large number of 
changes
in dma apis in recent kernels. I will let you and Robin decide if it's 
ok to
drop this change and introduce it later with a different patch.

Thanks,
Sai

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