> From: Liu, Yi L <yi.l.liu@xxxxxxxxx> > Sent: Tuesday, December 17, 2019 10:26 AM > To: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>; 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 > > > 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. BTW. The discussion in this thread may apply to other cache flush in your series. Please have a check. At least, there are two places which need to be updated in this single patch. Regards, Yi Liu
