linux-kernel - Re: [PATCH 1/1] iommu/arm-smmu-v3: add support for BBML

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Date:   Wed, 27 Jan 2021 09:39:38 +0000
From:   Robin Murphy <robin.murphy@....com>
To:     Keqian Zhu <zhukeqian1@...wei.com>, Will Deacon <will@...nel.org>
Cc:     Jean-Philippe Brucker <jean-philippe@...aro.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        iommu <iommu@...ts.linux-foundation.org>,
        Yang Yingliang <yangyingliang@...wei.com>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 1/1] iommu/arm-smmu-v3: add support for BBML

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,
> 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@...ts.infradead.org
>> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
>> .
>>
> _______________________________________________
> iommu mailing list
> iommu@...ts.linux-foundation.org
> https://lists.linuxfoundation.org/mailman/listinfo/iommu
> 

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