On Wed, Jul 01, 2026, Xiaoyao Li wrote:

On 6/27/2026 3:06 AM, Sean Christopherson wrote:

quoted

On Fri, Jun 26, 2026, Yan Zhao wrote:

quoted

My first impression of gmem_in_place_conversion=true was that it enforces gmem
in-place conversion. However, it actually only enforces per-gmem private/shared
attribute.
My worry was that people might think it's a kernel bug if userspace can still
have shared memory from other sources after they configured
gmem_in_place_conversion=true.

Ah, I see where you're coming from.  FWIW, truly enforcing in-place conversion
is flat out impossible.  E.g. userspace can simply replace the memslot, at which
point the memory effectively reverts to shared.

would something like below enforce the in-place conversion?

No.

Userspace can create a memslot without gmem fd, but that memslot can only
serve as shared memory and cannot be converted. So it doesn't violate the
in-place conversion.

But userspace can delete said memslot and replace it with a memslot pointing at
a guest_memfd instance that was created without INIT_SHARED, at which point
userspace has effected a shared=>private conversion.