> From: Jason Gunthorpe <jgg@xxxxxxxxxx> > Sent: Friday, March 18, 2022 10:13 PM > > On Fri, Mar 18, 2022 at 02:23:57AM +0000, Tian, Kevin wrote: > > > Yes, that is another major part work besides the iommufd work. And > > it is not compatible with KVM features which rely on the dynamic > > manner of EPT. Though It is a bit questionable whether it's worthy of > > doing so just for saving memory footprint while losing other capabilities, > > it is a requirement for some future security extension in Intel trusted > > computing architecture. And KVM has been pinning pages for SEV/TDX/etc. > > today thus some facilities can be reused. But I agree it is not a simple > > task thus we need start discussion early to explore various gaps in > > iommu and kvm. > > Yikes. IMHO this might work better going the other way, have KVM > import the iommu_domain and use that as the KVM page table than vice > versa. > > The semantics are a heck of a lot clearer, and it is really obvious > that alot of KVM becomes disabled if you do this. > This is an interesting angle to look at it. But given pinning is already required in KVM to support SEV/TDX even w/o assigned device, those restrictions have to be understood by KVM MMU code which makes a KVM-managed page table under such restrictions closer to be sharable with IOMMU. Thanks Kevin
