Messages in this thread |  | | Subject | Re: [PATCH v3 5/6] iommu/vt-d: Flush PASID-based iotlb for iova over first level | From | Lu Baolu <> | Date | Tue, 17 Dec 2019 09:37:22 +0800 |
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Hi again,
On 12/17/19 9:19 AM, Lu Baolu wrote: > Hi Yi, > > On 12/15/19 5:22 PM, Liu, Yi L wrote: >> Ok, let me explain more... default pasid is meaningful only when >> the domain has been attached to a device as an aux-domain. right? > > No exactly. Each domain has a specific default pasid, no matter normal > domain (RID based) or aux-domain (PASID based). The difference is for a > normal domain RID2PASID value is used, for an aux-domain the pasid is > allocated from a global pool. > > The same concept used in VT-d 3.x scalable mode. For RID based DMA > translation RID2PASID value is used when walking the tables; For PASID > based DMA translation a real pasid in the transaction is used. > >> If a domain only has one device, and it is attached to this device as >> normal domain (normal domain means non aux-domain here). Then >> you should flush cache with domain-id and RID2PASID value. >> If a domain has one device, and it is attached to this device as >> aux-domain. Then you may want to flush cache with domain-id >> and default pasid. right? > > A domain's counterpart is IOMMU group. So we say attach/detach domain > to/from devices in a group. We don't allow devices with different > default pasid sitting in a same group, right? > >> Then let's come to the case I mentioned in previous email. a mdev >> and another device assigned to a single VM. In host, you will have >> a domain which has two devices, one device(deva) is attached as > > No. We will have two IOMMU groups and two domains. Correct me if my > understanding is not right.
Reconsidered this. Unfortunately, my understanding is not right. :-(
A single domain could be attached to multiple IOMMU groups. So it comes to the issue you concerned. Do I understand it right?
> >> normal domain, another one (devB) is attached as aux-domain. Then >> which pasid should be used when the mapping in IOVA page table is >> modified? RID2PASID or default pasid? I think both should be used >> since the domain means differently to the two devices. If you just >> use default pasid, then deva may still be able to use stale caches.
You are right. I will change it accordingly. The logic should look like:
if (domain attached to physical device) flush_piotlb_with_RID2PASID() else if (domain_attached_to_mdev_device) flush_piotlb_with_default_pasid()
Does this work for you? Thanks for catching this!
Best regards, baolu
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