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

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Date:   Wed, 11 Aug 2021 21:36:12 +0530
From:   Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>
To:     Robin Murphy <robin.murphy@....com>, Will Deacon <will@...nel.org>
Cc:     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 21:23, Robin Murphy wrote:
> 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.
> 

I have dropped it and sent a v5.

Thanks,
Sai

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