On Fri, Jan 17, 2025 at 8:30 AM Fuad Tabba <tabba@xxxxxxxxxx> wrote: > > Before transitioning a guest_memfd folio to unshared, thereby > disallowing access by the host and allowing the hypervisor to > transition its view of the guest page as private, we need to be > sure that the host doesn't have any references to the folio. > > This patch introduces a new type for guest_memfd folios, and uses > that to register a callback that informs the guest_memfd > subsystem when the last reference is dropped, therefore knowing > that the host doesn't have any remaining references. > > Signed-off-by: Fuad Tabba <tabba@xxxxxxxxxx> > --- > The function kvm_slot_gmem_register_callback() isn't used in this > series. It will be used later in code that performs unsharing of > memory. I have tested it with pKVM, based on downstream code [*]. > It's included in this RFC since it demonstrates the plan to > handle unsharing of private folios. > > [*] https://android-kvm.googlesource.com/linux/+/refs/heads/tabba/guestmem-6.13-v5-pkvm Should the invocation of kvm_slot_gmem_register_callback() happen in the same critical block as setting the guest memfd range mappability to NONE, otherwise conversion/truncation could race with registration of callback?
