Re: [PATCH v3 00/24] KVM: TDX huge page support for private memory

[Sean Christopherson <seanjc@google.com>]

On Mon, Jan 19, 2026, Yan Zhao wrote:
> On Sat, Jan 17, 2026 at 12:58:02AM +0800, Edgecombe, Rick P wrote:
> > On Fri, 2026-01-16 at 08:31 -0800, Sean Christopherson wrote:
> IIUC, this concern should be gone as Dave has agreed to use "pfn" as the
> SEAMCALL parameter [1]?
> Then should we invoke "KVM_MMU_WARN_ON(!tdx_is_convertible_pfn(pfn));" in KVM
> for every pfn of a huge mapping? Or should we keep the sanity check inside the
> SEAMCALL wrappers?

I don't have a strong preference.  But if it goes in KVM, definitely guard it with
KVM_MMU_WARN_ON().

> BTW, I have another question about the SEAMCALL wrapper implementation, as Kai
> also pointed out in [2]: since the SEAMCALL wrappers now serve as APIs available
> to callers besides KVM, should the SEAMCALL wrappers return TDX_OPERAND_INVALID
> or WARN_ON() (or WARN_ON_ONCE()) on sanity check failure?

Why not both?  But maybe TDX_SW_ERROR instead of TDX_OPERAND_INVALID?

If an API has a defined contract and/or set of expectations, and those expectations
aren't met by the caller, then a WARN is justified.  But the failure still needs
to be communicated to the caller.

> By returning TDX_OPERAND_INVALID, the caller can check the return code, adjust
> the input or trigger WARN_ON() by itself;
> By triggering WARN_ON() directly in the SEAMCALL wrapper, we need to document
> this requirement for the SEAMCALL wrappers and have the caller invoke the API
> correctly.

Document what exactly?  Most of this should be common sense.  E.g. we don't generally
document that pointers must be non-NULL, because that goes without saying 99.9%
of the time.

IMO, that holds true here as well.  E.g. trying to map memory into a TDX guest
that isn't convertible is obviously a bug, I don't see any value in formally
documenting that requirement.

> So, it looks that "WARN_ON() directly in the SEAMCALL wrapper" is the preferred
> approach, right?

> 
> [1] https://lore.kernel.org/all/d119c824-4770-41d2-a926-4ab5268ea3a6@intel.com/
> [2] https://lore.kernel.org/all/baf6df2cc63d8e897455168c1bf07180fc9c1db8.camel@intel.com