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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: <d3aaa7e7-edb0-f867-0519-9a4e0bee35d2@huawei.com>
Date:   Thu, 28 Jan 2021 23:18:46 +0800
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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.

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
>>> .
>>>
>> _______________________________________________
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>> iommu@lists.linux-foundation.org
>> https://lists.linuxfoundation.org/mailman/listinfo/iommu
>>
> .
>