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 12:13:35 +0800 |
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Hi,
On 2019/12/17 10:36, Liu, Yi L wrote: >> From: Liu, Yi L <yi.l.liu@intel.com> >> Sent: Tuesday, December 17, 2019 10:26 AM >> To: Lu Baolu <baolu.lu@linux.intel.com>; Joerg Roedel <joro@8bytes.org>; David >> Woodhouse <dwmw2@infradead.org>; Alex Williamson >> <alex.williamson@redhat.com> >> Subject: RE: [PATCH v3 5/6] iommu/vt-d: Flush PASID-based iotlb for iova over first >> level >> >>> From: Lu Baolu [mailto:baolu.lu@linux.intel.com] >>> Sent: Tuesday, December 17, 2019 9:37 AM >>> To: Liu, Yi L <yi.l.liu@intel.com>; Joerg Roedel <joro@8bytes.org>; David >>> Woodhouse <dwmw2@infradead.org>; Alex Williamson >>> <alex.williamson@redhat.com> >>> 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.
Sure. I will.
Best regards,
baolu > > Regards, > Yi Liu
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