Sean Christopherson wrote: > On Fri, Jul 11, 2025, Ira Weiny wrote: > > Michael Roth wrote: > > > For in-place conversion: the idea is that userspace will convert > > > private->shared to update in-place, then immediately convert back > > > shared->private; > > > > Why convert from private to shared and back to private? Userspace which > > knows about mmap and supports it should create shared pages, mmap, write > > data, then convert to private. > > Dunno if there's a strong usecase for converting to shared *and* populating the > data, but I also don't know that it's worth going out of our way to prevent such > behavior, at least not without a strong reason to do so. I'm not proposing to prevent such behavior. Only arguing that the private->shared->private path to data population is unlikely to be a 'common' use case. > E.g. if it allowed for > a cleaner implementation or better semantics, then by all means. But I don't > think that's true here? Though I haven't thought hard about this, so don't > quote me on that. :-) Me neither. Since I am new to this I am looking at this from a pretty hight level and it seems to me if the intention is to pass data to the guest then starting shared is the way to go. Passing data out, in a Coco VM, is probably not going to be supported. I have to think on Vishal's assertion that a shared page needs to be split on allocation. That does not make sense to me. > > Old userspace will create private and pass in a source pointer for the > > initial data as it does today. > > > > Internally, the post_populate() callback only needs to know if the data is > > in place or coming from somewhere else (ie src != NULL). > > I think there will be a third option: data needs to be zeroed, i.e. the !src && > !PRESERVED case. Yes, indeed. Ira
