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Subject: Re: [PATCH 1/1] iommu/arm-smmu-v3: add support for BBML
To:     Robin Murphy <robin.murphy@arm.com>, Will Deacon <will@kernel.org>
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CC:     Jean-Philippe Brucker <jean-philippe@linaro.org>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        iommu <iommu@lists.linux-foundation.org>,
        Yang Yingliang <yangyingliang@huawei.com>,
        linux-arm-kernel <linux-arm-kernel@lists.infradead.org>
From:   Keqian Zhu <zhukeqian1@huawei.com>
Message-ID: <29fd5c20-faeb-1fd3-6535-4fca60463d01@huawei.com>
Date:   Fri, 29 Jan 2021 14:12:46 +0800
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On 2021/1/29 0:17, Robin Murphy wrote:
> On 2021-01-28 15:18, Keqian Zhu wrote:
>>
>>
>> On 2021/1/27 17:39, Robin Murphy wrote:
>>> On 2021-01-27 07:36, Keqian Zhu wrote:
>>>>
>>>>
>>>> On 2021/1/27 10:01, Leizhen (ThunderTown) wrote:
>>>>>
>>>>>
>>>>> On 2021/1/26 18:12, Will Deacon wrote:
>>>>>> On Mon, Jan 25, 2021 at 08:23:40PM +0000, Robin Murphy wrote:
>>>>>>> Now we probably will need some degreee of BBML feature awareness for the
>>>>>>> sake of SVA if and when we start using it for CPU pagetables, but I still
>>>>>>> cannot see any need to consider it in io-pgtable.
>>>>>>
>>>>>> Agreed; I don't think this is something that io-pgtable should have to care
>>>>>> about.
>>>> Hi,
>>>>
>>>> I have a question here :-).
>>>> If the old table is not live, then the break procedure seems unnecessary. Do I miss something?
>>>
>>> The MMU is allowed to prefetch translations at any time, so not following the proper update procedure could still potentially lead to a TLB conflict, even if there's no device traffic to worry about disrupting.
>>>
>>> Robin.
>>
>> Thanks. Does the MMU you mention here includes MMU and SMMU? I know that at SMMU side, ATS can prefetch translation.
> 
> Yes, both - VMSAv8 allows speculative translation table walks, so SMMUv3 inherits from there (per 3.21.1 "Translation tables and TLB invalidation completion behavior").
OK, I Get it. Thanks.

Keqian.

> 
> Robin.
> 
>>
>> Keqian
>>>
>>>> Thanks,
>>>> Keqian
>>>>
>>>>>
>>>>> Yes, the SVA works in stall mode, and the failed device access requests are not
>>>>> discarded.
>>>>>
>>>>> Let me look for examples. The BBML usage scenario was told by a former colleague.
>>>>>
>>>>>>
>>>>>> Will
>>>>>>
>>>>>> .
>>>>>>
>>>>>
>>>>>
>>>>> _______________________________________________
>>>>> linux-arm-kernel mailing list
>>>>> linux-arm-kernel@lists.infradead.org
>>>>> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
>>>>> .
>>>>>
>>>> _______________________________________________
>>>> iommu mailing list
>>>> iommu@lists.linux-foundation.org
>>>> https://lists.linuxfoundation.org/mailman/listinfo/iommu
>>>>
>>> .
>>>
> .
>