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

From: Keqian Zhu <zhukeqian1@huawei.com>
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>
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>
Subject: Re: [RFC PATCH v4 01/13] iommu: Introduce dirty log tracking framework
Date: Thu, 13 May 2021 18:58:03 +0800	[thread overview]
Message-ID: <bbc1960c-24f3-680a-b6ff-c81f70fa9c04@huawei.com> (raw)
In-Reply-To: <7fb678c7-509b-dbb5-d533-32c5ce2a0476@linux.intel.com>

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.

Thanks,
Keqian