On Mon, Dec 11, 2023 at 08:36:46PM +0800, Yi Liu wrote: > On 2023/12/11 10:29, Tian, Kevin wrote: > > > From: Jason Gunthorpe <jgg@xxxxxxxxxx> > > > Sent: Saturday, December 9, 2023 9:47 AM > > > > > > What is in a Nested domain: > > > Intel: A single IO page table refereed to by a PASID entry > > > Each vDomain-ID,PASID allocates a unique nesting domain > > > AMD: A GCR3 table pointer > > > Nesting domains are created for every unique GCR3 pointer. > > > vDomain-ID can possibly refer to multiple Nesting domains :( > > > ARM: A CD table pointer > > > Nesting domains are created for every unique CD table top pointer. > > > > this AMD/ARM difference is not very clear to me. > > > > How could a vDomain-ID refer to multiple GCR3 pointers? Wouldn't it > > lead to cache tag conflict when a same PASID entry in multiple GCR3 tables > > points to different I/O page tables? > > Perhaps due to only one DomainID in the DTE table indexed by BDF? Actually, > the vDomainID will not be used to tag cache, the host DomainId would be > used instead. @Jason? The DomainID comes from the DTE table which is indexed by the RID, and the DTE entry points to the GCR3 table. So the VM certainly can setup a DTE table with multiple entires having the same vDomainID but pointing to different GCR3's. So the VMM has to do *something* with this. Most likely this is not a useful thing to do. However what should the VMM do when it sees this? Block a random DTE or push the duplication down to real HW would be my options. I'd probably try to do the latter just on the basis of better emulation. Jason
