Re: [PATCH v3 5/6] iommu/vt-d: Flush PASID-based iotlb for iova over first level

[Lu Baolu]

Hi,

On 2019/12/17 10:36, Liu, Yi L wrote:
> > 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.

Sure. I will.

Best regards,

baolu
>   
> Regards,
> Yi Liu