Hi Ackerley,
On Wed, 12 Feb 2025 at 00:15, Ackerley Tng <ackerleytng@xxxxxxxxxx> wrote:
>
> Fuad Tabba <tabba@xxxxxxxxxx> writes:
>
> > For VMs that allow sharing guest_memfd backed memory in-place,
> > handle that memory the same as "private" guest_memfd memory. This
> > means that faulting that memory in the host or in the guest will
> > go through the guest_memfd subsystem.
> >
> > Note that the word "private" in the name of the function
> > kvm_mem_is_private() doesn't necessarily indicate that the memory
> > isn't shared, but is due to the history and evolution of
> > guest_memfd and the various names it has received. In effect,
> > this function is used to multiplex between the path of a normal
> > page fault and the path of a guest_memfd backed page fault.
> >
>
> Thanks for this summary! It has always been confusing and this really
> helps.
>
> Is there any chance we could rename the functions in KVM, or maybe add a
> comment at the function definitions? The name of the userspace flag will
> have to remain, of course.
Actually, I was thinking of doing that in V4. Rename, or at least add
an alias, as a separate patch, to see what the community thinks.
Since, even with this comment, it is still confusing (as
evidenced by Quentin's comment on the later patch).
Cheers,
/fuad
> > Signed-off-by: Fuad Tabba <tabba@xxxxxxxxxx>
> > ---
> > include/linux/kvm_host.h | 3 ++-
> > 1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> > index 438aa3df3175..39fd6e35c723 100644
> > --- a/include/linux/kvm_host.h
> > +++ b/include/linux/kvm_host.h
> > @@ -2521,7 +2521,8 @@ static inline bool kvm_mem_is_private(struct kvm *kvm, gfn_t gfn)
> > #else
> > static inline bool kvm_mem_is_private(struct kvm *kvm, gfn_t gfn)
> > {
> > - return false;
> > + return kvm_arch_gmem_supports_shared_mem(kvm) &&
> > + kvm_slot_can_be_private(gfn_to_memslot(kvm, gfn));
> > }
> > #endif /* CONFIG_KVM_GENERIC_MEMORY_ATTRIBUTES */
