Messages in this thread | | | Subject | Re: [RFC PATCH v4 01/13] iommu: Introduce dirty log tracking framework | From | Lu Baolu <> | Date | Tue, 11 May 2021 11:12:07 +0800 |
| |
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.
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.
> >> 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.
Best regards, baolu
| |