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Subject: Re: [PATCH 1/1] iommu/arm-smmu-v3: add support for BBML
To:     Keqian Zhu <zhukeqian1@huawei.com>, Will Deacon <will@kernel.org>
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>
References: <20201126034230.777-1-thunder.leizhen@huawei.com>
 <20210122125132.GB24102@willie-the-truck>
 <aac11411-f6cd-f990-fe53-db0d8c07f3a0@huawei.com>
 <1bfd1ca0-953e-e943-f87e-144d5537bd0c@arm.com>
 <20210126101230.GA29204@willie-the-truck>
 <8a9685ec-67aa-824f-5429-f408bf79c5ab@huawei.com>
 <32f4752f-6954-183a-a0c1-b5d719c85b67@huawei.com>
From:   Robin Murphy <robin.murphy@arm.com>
Message-ID: <319e3532-4555-7431-9d6f-3c3b7c11a5d9@arm.com>
Date:   Wed, 27 Jan 2021 09:39:38 +0000
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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@lists.infradead.org
>> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
>> .
>>
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