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

[Yan Zhao <yan.y.zhao@intel.com>]

On Tue, Jun 30, 2026 at 02:37:11PM -0700, 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.
> 
> 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@intel.com>
> Cc: Ackerley Tng <ackerleytng@google.com>
> Signed-off-by: Sean Christopherson <seanjc@google.com>

Reviewed-by: Yan Zhao <yan.y.zhao@intel.com>
Tested-by: Yan Zhao <yan.y.zhao@intel.com>

> ---
>  arch/x86/kvm/vmx/tdx.c | 7 ++-----
>  1 file changed, 2 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
> index ffe9d0db58c5..b0ec054732b9 100644
> --- a/arch/x86/kvm/vmx/tdx.c
> +++ b/arch/x86/kvm/vmx/tdx.c
> @@ -3198,9 +3198,6 @@ static int tdx_gmem_post_populate(struct kvm *kvm, gfn_t gfn, kvm_pfn_t pfn,
>  	if (KVM_BUG_ON(kvm_tdx->page_add_src, kvm))
>  		return -EIO;
>  
> -	if (!src_page)
> -		return -EOPNOTSUPP;
> -
>  	kvm_tdx->page_add_src = src_page;
>  	ret = kvm_tdp_mmu_map_private_pfn(arg->vcpu, gfn, pfn);
>  	kvm_tdx->page_add_src = NULL;
> @@ -3247,8 +3244,8 @@ static int tdx_vcpu_init_mem_region(struct kvm_vcpu *vcpu, struct kvm_tdx_cmd *c
>  	if (copy_from_user(&region, u64_to_user_ptr(cmd->data), sizeof(region)))
>  		return -EFAULT;
>  
> -	if (!PAGE_ALIGNED(region.source_addr) || !PAGE_ALIGNED(region.gpa) ||
> -	    !region.nr_pages ||
> +	if (!PAGE_ALIGNED(region.source_addr) || !region.source_addr ||
> +	    !PAGE_ALIGNED(region.gpa) || !region.nr_pages ||
>  	    region.gpa + (region.nr_pages << PAGE_SHIFT) <= region.gpa ||
>  	    !vt_is_tdx_private_gpa(kvm, region.gpa) ||
>  	    !vt_is_tdx_private_gpa(kvm, region.gpa + (region.nr_pages << PAGE_SHIFT) - 1))
> -- 
> 2.55.0.rc0.799.gd6f94ed593-goog
>