Re: [PATCH v2 2/2] KVM: TDX: Return EINVAL, not EOPNOTSUPP, for NULL INIT_MEM_REGION source

[Sean Christopherson]

On Wed, Jul 01, 2026, Binbin Wu wrote:
> On 7/1/2026 5:37 AM, Sean Christopherson wrote:
> > Return EINVAL instead of EOPNOTSUPP if userspace attempts to pass a NULL
> > pointer for the source page of INIT_MEM_REGION, so that KVM's ABI is
> > consistent between TDX and SNP (for LAUNCH_UPDATE).  EOPNOTSUPP was chosen
> > to be a forward-looking error code for when guest_memfd supports in-place
> > conversion, but even when in-place conversion comes along, it's an awkward
> > error code as KVM is deliberately choosing to disallow virtual address '0',
> > which is technically a legal userspace address.  I.e. it's not so much a
> > lack of support as it is that KVM reserves address '0' to simplify KVM's
> > internal implementation.
> 
> Nit:
> Do you think it's worth calling this out in the documentation?

Yes, though that can be done separate since this series doesn't change ABI.
E.g. we can probably do it opportunistically as part of the in-place conversion
series?