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

[Binbin Wu]

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?

> 
> Opportunistically move the check so that it's co-located with the other
> checks on the userspace address, and so that it's more obvious that a NULL
> source address is explicitly disallowed.
> 
> Fixes: 2a62345b3052 ("KVM: guest_memfd: GUP source pages prior to populating guest memory")
> Cc: Yan Zhao <yan.y.zhao@xxxxxxxxx>
> Cc: Ackerley Tng <ackerleytng@xxxxxxxxxx>
> Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>

Reviewed-by: Binbin Wu <binbin.wu@xxxxxxxxxxxxxxx>