linux-kernel - Re: [PATCH v4 4/5] iommu/arm-smmu-v3: add support for non-strict mode

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Message-ID: <5B723517.3010603@huawei.com>
Date:   Tue, 14 Aug 2018 09:49:11 +0800
From:   "Leizhen (ThunderTown)" <thunder.leizhen@...wei.com>
To:     Robin Murphy <robin.murphy@....com>,
        Will Deacon <will.deacon@....com>,
        Joerg Roedel <joro@...tes.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        iommu <iommu@...ts.linux-foundation.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
CC:     LinuxArm <linuxarm@...wei.com>, Hanjun Guo <guohanjun@...wei.com>,
        Libin <huawei.libin@...wei.com>
Subject: Re: [PATCH v4 4/5] iommu/arm-smmu-v3: add support for non-strict mode



On 2018/8/9 19:06, Robin Murphy wrote:
> On 06/08/18 13:27, Zhen Lei wrote:
>> Dynamically choose strict or non-strict mode for page table config based
>> on the iommu domain type.
>>
>> Signed-off-by: Zhen Lei <thunder.leizhen@...wei.com>
>> ---
>>   drivers/iommu/arm-smmu-v3.c | 7 ++++++-
>>   1 file changed, 6 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/iommu/arm-smmu-v3.c b/drivers/iommu/arm-smmu-v3.c
>> index 2f1304b..904bc1e 100644
>> --- a/drivers/iommu/arm-smmu-v3.c
>> +++ b/drivers/iommu/arm-smmu-v3.c
>> @@ -1622,6 +1622,11 @@ static int arm_smmu_domain_finalise(struct iommu_domain *domain)
>>       if (smmu->features & ARM_SMMU_FEAT_COHERENCY)
>>           pgtbl_cfg.quirks = IO_PGTABLE_QUIRK_NO_DMA;
>>
>> +    if (domain->type == IOMMU_DOMAIN_DMA) {
>> +        domain->non_strict = 1;
>> +        pgtbl_cfg.quirks |= IO_PGTABLE_QUIRK_NON_STRICT;
>> +    }
>> +
>>       pgtbl_ops = alloc_io_pgtable_ops(fmt, &pgtbl_cfg, smmu_domain);
>>       if (!pgtbl_ops)
>>           return -ENOMEM;
>> @@ -1782,7 +1787,7 @@ static void arm_smmu_iotlb_sync(struct iommu_domain *domain)
>>   {
>>       struct arm_smmu_device *smmu = to_smmu_domain(domain)->smmu;
>>
>> -    if (smmu)
>> +    if (smmu && !domain->non_strict)
> 
> That doesn't smell right - even in non-strict domains we still need stuff like walk cache invalidations for non-leaf unmaps to be synchronous, so we can't just ignore all sync operations at the driver level. I think the right thing to do to elide the "normal" sync on unmap is to first convert __iommu_dma_unmap to use iommu_unmap_fast()/iommu_tlb_sync(), then make it not issue that sync at all for non-strict domains.

OK, I will try it.

> 
> Robin.
> 
>>           __arm_smmu_tlb_sync(smmu);
>>   }
>>
>> -- 
>> 1.8.3
>>
>>
> 
> .
> 

-- 
Thanks!
BestRegards