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Subject: Re: [RFC PATCH v4 01/13] iommu: Introduce dirty log tracking
 framework
To:     Keqian Zhu <zhukeqian1@huawei.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>
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From:   Lu Baolu <baolu.lu@linux.intel.com>
Message-ID: <7fb678c7-509b-dbb5-d533-32c5ce2a0476@linux.intel.com>
Date:   Wed, 12 May 2021 19:36:10 +0800
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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.

Best regards,
baolu