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Subject: Re: [RFC PATCH v4 01/13] iommu: Introduce dirty log tracking
 framework
To:     Lu Baolu <baolu.lu@linux.intel.com>,
        <linux-kernel@vger.kernel.org>,
        <linux-arm-kernel@lists.infradead.org>,
        <iommu@lists.linux-foundation.org>,
        Robin Murphy <robin.murphy@arm.com>,
        Will Deacon <will@kernel.org>,
        "Joerg Roedel" <joro@8bytes.org>,
        Jean-Philippe Brucker <jean-philippe@linaro.org>,
        Yi Sun <yi.y.sun@linux.intel.com>,
        Tian Kevin <kevin.tian@intel.com>
References: <20210507102211.8836-1-zhukeqian1@huawei.com>
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 <18ac787a-179e-71f7-728b-c43feda80a16@huawei.com>
 <55fda826-9ab6-a3a0-b17e-a4d4879f00bc@linux.intel.com>
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 <f47e90c6-f3c4-b28f-a810-e03afe79e62d@linux.intel.com>
 <60182a35-e151-7150-3708-4e58dd8e78da@huawei.com>
 <36cc7267-6aa3-db54-b08c-c2dfc0bbacb6@linux.intel.com>
 <e38f1837-b814-3717-2faf-4df8349cb57c@huawei.com>
 <7fb678c7-509b-dbb5-d533-32c5ce2a0476@linux.intel.com>
 <bbc1960c-24f3-680a-b6ff-c81f70fa9c04@huawei.com>
 <ce19e7a0-e7b7-aa09-b074-ad555d42bab2@linux.intel.com>
CC:     Alex Williamson <alex.williamson@redhat.com>,
        Kirti Wankhede <kwankhede@nvidia.com>,
        Cornelia Huck <cohuck@redhat.com>,
        Jonathan Cameron <Jonathan.Cameron@huawei.com>,
        <wanghaibin.wang@huawei.com>, <jiangkunkun@huawei.com>,
        <yuzenghui@huawei.com>, <lushenming@huawei.com>
From:   Keqian Zhu <zhukeqian1@huawei.com>
Message-ID: <81d0731d-3331-a5f4-1867-5cc1f3f97a29@huawei.com>
Date:   Fri, 14 May 2021 10:30:17 +0800
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On 2021/5/13 20:02, Lu Baolu wrote:
> On 5/13/21 6:58 PM, Keqian Zhu wrote:
>>
>>
>> On 2021/5/12 19:36, Lu Baolu wrote:
>>> Hi keqian,
>>>
>>> On 5/12/21 4:44 PM, Keqian Zhu wrote:
>>>>
>>>>
>>>> On 2021/5/12 11:20, Lu Baolu wrote:
>>>>> On 5/11/21 3:40 PM, Keqian Zhu wrote:
>>>>>>> For upper layers, before starting page tracking, they check the
>>>>>>> dirty_page_trackable attribution of the domain and start it only it's
>>>>>>> capable. Once the page tracking is switched on the vendor iommu driver
>>>>>>> (or iommu core) should block further device attach/detach operations
>>>>>>> until page tracking is stopped.
>>>>>> But when a domain becomes capable after detaching a device, the upper layer
>>>>>> still needs to query it and enable dirty log for it...
>>>>>>
>>>>>> To make things coordinated, maybe the upper layer can register a notifier,
>>>>>> when the domain's capability change, the upper layer do not need to query, instead
>>>>>> they just need to realize a callback, and do their specific policy in the callback.
>>>>>> What do you think?
>>>>>>
>>>>>
>>>>> That might be an option. But why not checking domain's attribution every
>>>>> time a new tracking period is about to start?
>>>> Hi Baolu,
>>>>
>>>> I'll add an attribution in iommu_domain, and the vendor iommu driver will update
>>>> the attribution when attach/detach devices.
>>>>
>>>> The attribute should be protected by a lock, so the upper layer shouldn't access
>>>> the attribute directly. Then the iommu_domain_support_dirty_log() still should be
>>>> retained. Does this design looks good to you?
>>>
>>> Yes, that's what I was thinking of. But I am not sure whether it worth
>>> of a lock here. It seems not to be a valid behavior for upper layer to
>>> attach or detach any device while doing the dirty page tracking.
>> Hi Baolu,
>>
>> Right, if the "detach|attach" interfaces and "dirty tracking" interfaces can be called concurrently,
>> a lock in iommu_domain_support_dirty_log() is still not enough. I will add another note for the dirty
>> tracking interfaces.
>>
>> Do you have other suggestions? I will accelerate the progress, so I plan to send out v5 next week.
> 
> No further comments expect below nit:
> 
> "iommu_switch_dirty_log: Perform actions to start|stop dirty log tracking"
> 
> How about splitting it into
>  - iommu_start_dirty_log()
>  - iommu_stop_dirty_log()
Yeah, actually this is my original version, and the "switch" style is suggested by Yi Sun.
Anyway, I think both is OK, and the "switch" style can reduce some code.

Thanks,
Keqian

> 
> Not a strong opinion anyway.
> 
> Best regards,
> baolu
> .
>