Hi Baolu, On 2021/5/11 11:12, Lu Baolu wrote: > Hi Keqian, > > On 5/10/21 7:07 PM, Keqian Zhu wrote: >>>>> I suppose this interface is to ask the vendor IOMMU driver to check >>>>> whether each device/iommu in the domain supports dirty bit tracking. >>>>> But what will happen if new devices with different tracking capability >>>>> are added afterward? >>>> Yep, this is considered in the vfio part. We will query again after >>>> attaching or >>>> detaching devices from the domain. When the domain becomes capable, we >>>> enable >>>> dirty log for it. When it becomes not capable, we disable dirty log for it. >>> If that's the case, why not putting this logic in the iommu subsystem so >>> that it doesn't need to be duplicate in different upper layers? >>> >>> For example, add something like dirty_page_trackable in the struct of >>> iommu_domain and ask the vendor iommu driver to update it once any >>> device is added/removed to/from the domain. It's also better to disallow >> If we do it, the upper layer still needs to query the capability from domain >> and switch >> dirty log tracking for it. Or do you mean the domain can switch dirty log >> tracking automatically >> when its capability change? If so, I think we're lack of some flexibility. >> The upper layer >> may have it's own policy, such as only enable dirty log tracking when all >> domains are capable, >> and disable dirty log tracking when just one domain is not capable. > > I may not get you. > > Assume that dirty_page_trackable is an attribution of an iommu_domain. > This attribution might be changed once a new device (with different > capability) added or removed. So it should be updated every time a new > device is attached or detached. This work could be done by the vendor > iommu driver on the path of dev_attach/dev_detach callback. Yes, this is what I understand you.
> > 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? > >> >>> any domain attach/detach once the dirty page tracking is on. >> Yep, this can greatly simplify our code logic, but I don't know whether our >> maintainers >> agree that, as they may think that IOMMU dirty logging should not change >> original domain >> behaviors. > > The maintainer owns the last word, but we need to work out a generic and > self-contained API set. OK, I see. Thanks, Keqian _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu