> From: Lu Baolu [mailto:baolu.lu@xxxxxxxxxxxxxxx] > Sent: Tuesday, December 17, 2019 9:37 AM > To: Liu, Yi L <yi.l.liu@xxxxxxxxx>; Joerg Roedel <joro@xxxxxxxxxx>; David > Woodhouse <dwmw2@xxxxxxxxxxxxx>; Alex Williamson > <alex.williamson@xxxxxxxxxx> > Subject: Re: [PATCH v3 5/6] iommu/vt-d: Flush PASID-based iotlb for iova over first > level > > 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? yes. Device within the same group has no such issue since such devices are not able to enabled aux-domain. Now our understanding are aligned. :-) > > > >> 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! If no else, it would work for scalable mode. ^_^ I noticed you've already corrected by yourself in another reply. :-) Look forward to your next version. Regards, Yi Liu
