Re: [RFC PATCH] KVM: TDX: Decouple TDX init mem region from kvm_gmem_populate()

[Sean Christopherson <seanjc@google.com>]

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.  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. :-)

> 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.