> From: Jason Gunthorpe <jgg@xxxxxxxxxx> > Sent: Friday, March 18, 2022 9:46 PM > > On Fri, Mar 18, 2022 at 07:01:19AM +0000, Tian, Kevin wrote: > > > From: Jason Gunthorpe <jgg@xxxxxxxxxx> > > > Sent: Tuesday, March 15, 2022 10:55 PM > > > > > > The first level iommu_domain has the 'type1' map and unmap and pins > > > the pages. This is the 1:1 map with the GPA and ends up pinning all > > > guest memory because the point is you don't want to take a memory pin > > > on your performance path > > > > > > The second level iommu_domain points to a single IO page table in GPA > > > and is created/destroyed whenever the guest traps to the hypervisor to > > > manipulate the anchor (ie the GPA of the guest IO page table). > > > > > > > Can we use consistent terms as used in iommufd and hardware, i.e. > > with first-level/stage-1 referring to the child (GIOVA->GPA) which is > > further nested on second-level/stage-2 as the parent (GPA->HPA)? > > Honestly I don't like injecting terms that only make sense for > virtualization into iommu/vfio land. 1st/2nd-level or stage-1/2 are hardware terms not tied to virtualization. GIOVA/GPA are just examples in this story. > > That area is intended to be general. If you use what it exposes for > virtualization, then great. > > This is why I prefer to use 'user page table' when talking about the > GIOVA->GPA or Stage 1 map because it is a phrase independent of > virtualization or HW and clearly conveys what it is to the kernel and > its inherent order in the translation scheme. I fully agree with this point. The confusion only comes when you start talking about first/second level in a way incompatible with what iommu/vfio guys typically understand. 😊 > > The S1/S2 is gets confusing because the HW people choose those names > so that S1 is the first translation a TLP sees and S2 is the second. > > But from a software model, the S2 is the first domain created and the > first level of the translation tree, while the S1 is the second domain > created and the second level of the translation tree. ie the natural > SW numbers are backwards. Yes, I got this point. > > And I know Matthew isn't working on HW that has the S1/S2 HW naming :) > > But yes, should try harder to have good names. Maybe it will be > clearer with code. > Yes. let's try to use 'user page table' as possible. But if the levels/stages are inevitable in description I prefer to staying with the hardware terms given iommu driver has to deal with hardware naming things. Thanks Kevin
