Re: [PATCH v3] x86/virt/tdx: Formalize SEAMCALL version encoding support

[Nikolay Borisov]

On 7/22/26 11:46, Xu Yilun wrote:
> SEAMCALL invokes TDX module functions using a function number and
> parameters. To extend the functionality of existing SEAMCALLs while
> keeping backward compatibility, TDX adds more numbered SEAMCALLs of the
> same family. This is just like syscalls, except that TDX defines a
> specific function number encoding pattern: a base function number and a
> version together encode the full function number.
>
> One concern is the compatibility with older TDX modules which don't
> recognize the new SEAMCALLs. The kernel should decide which SEAMCALL
> version to use at runtime, selecting the minimum version number for the
> required functionality. It can't overwrite the function number with a
> new value at compile time.
>
> Another concern is the obscure usage of the 'fn' parameter for SEAMCALL
> wrappers. An existing caller for TDH.VP.INIT packs the version into the
> 'fn' to match the low-level TDX ABI RAX layout. The RAX layout
> interprets some bits differently, such as INTERRUPT_MODE, SEAMLDR flag,
> which are not a good fit for the function number definition.
>
> Refactor the SEAMCALL wrappers to allow for version selection. Add a
> version field in struct tdx_module_args [1], so that most existing
> callers get a default "version == 0" behavior without code churn, while
> callers requiring extended functionalities can specify the version
> descriptively. Enforce the 'fn' parameter as the base function number.
> Encode the base function number and tdx_module_args.version in RAX
> before invoking the SEAMCALL instruction in assembly code.
>
> Link: https://lore.kernel.org/kvm/4f4b0f29-424b-45ed-8cfd-c77da2ea390f@xxxxxxxxx/ # [1]
> Signed-off-by: Xu Yilun <yilun.xu@xxxxxxxxxxxxxxx>
> ---

Reviewed-by: Nikolay Borisov <nik.borisov@xxxxxxxx>