Re: [RFC PATCH v2 04/51] KVM: guest_memfd: Introduce KVM_GMEM_CONVERT_SHARED/PRIVATE ioctls

[Xu Yilun]

> > > 
> > > Only *guest permitted* conversion should change the page. I.e only when
> > > VMM is dealing with the KVM_HC_MAP_GPA_RANGE hypercall. Not sure if we
> > > could just let QEMU ensure this or KVM/guestmemfd should ensure this.
> > 
> > I think it should not be part of the kernel, no need. From a kernel
> > perspective userspace has requested a shared/private conversion and if
> > it wasn't agreed with the VM then it will explode.
> 
> I'm OK with it now. It's simple if we don't try to recover from the
> explosion. Although I see the after explosion processing in kernel is
> complex and not sure how it will advance.

I see the discussion in another thread about similar issue. That TDX
Module BUG causes S-EPT unmap impossible and just KVM_BUG_ON(). But this
conversion issue is a little different, usually it's not decent to panic
because of userspace request. So may need further error handling, or a
KVM/gmemfd kAPI to disallow/allow conversion and prevent more complex
error.

Thanks,
Yilun

> 
> Thanks,
> Yilun
> 
> > 
> > Jason
>