linux-kernel - Re: [RFC PATCH v4 01/13] iommu: Introduce dirty log tracking framework

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Date:   Thu, 13 May 2021 20:02:47 +0800
From:   Lu Baolu <baolu.lu@...ux.intel.com>
To:     Keqian Zhu <zhukeqian1@...wei.com>, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        iommu@...ts.linux-foundation.org,
        Robin Murphy <robin.murphy@....com>,
        Will Deacon <will@...nel.org>, Joerg Roedel <joro@...tes.org>,
        Jean-Philippe Brucker <jean-philippe@...aro.org>,
        Yi Sun <yi.y.sun@...ux.intel.com>,
        Tian Kevin <kevin.tian@...el.com>
Cc:     baolu.lu@...ux.intel.com,
        Alex Williamson <alex.williamson@...hat.com>,
        Kirti Wankhede <kwankhede@...dia.com>,
        Cornelia Huck <cohuck@...hat.com>,
        Jonathan Cameron <Jonathan.Cameron@...wei.com>,
        wanghaibin.wang@...wei.com, jiangkunkun@...wei.com,
        yuzenghui@...wei.com, lushenming@...wei.com
Subject: Re: [RFC PATCH v4 01/13] iommu: Introduce dirty log tracking
 framework

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()

Not a strong opinion anyway.

Best regards,
baolu