Re: [PATCH v2 02/17] x86/virt/tdx: Configure add-on features on TDX module init and update

[Dave Hansen]

On 6/18/26 01:13, Xu Yilun wrote:
>  int tdx_module_run_update(void)
>  {
> +	u64 seamcall_fn = TDH_SYS_UPDATE_V0;
>  	struct tdx_module_args args = {};
>  	int ret;
>  
> -	ret = seamcall_prerr(TDH_SYS_UPDATE, &args);
> +	if (tdx_addon_feature0) {
> +		args.r9 = tdx_addon_feature0;
> +		seamcall_fn = TDH_SYS_UPDATE;
> +	}

Heh, and it falls apart into craziness immediately. See how it
immediately loses the logical information that there's a version 1 and a
version 0? The "1" isn't even visible. It's hidden in "TDH_SYS_UPDATE".

Isn't this a million times more sane?

	struct tdx_module_args args = {};
	u64 version;
  	int ret;

	if (tdx_addon_feature0) {
		args.r9 = tdx_addon_feature0;
		version = 1;
	} else {
		version = 0;
	}

	ret = seamcall_prerr(TDH_SYS_UPDATE, version, &args);


There's also zero stopping us from putting version in args:

	struct tdx_module_args args = {};
  	int ret;

	if (tdx_addon_feature0) {
		args.r9 = tdx_addon_feature0;
		args.version = 1;
	}

	ret = seamcall_prerr(TDH_SYS_UPDATE, &args);

Eh?

That gives args.version==0 in all the normal cases which just happens to
be the exact behavior we want. It also avoids having to plumb version
through all the seamcall*() wrappers.

But this is *exactly* the kind of thing that shouldn't be a part of an
attestation patch series. This could very much have been a separate
discussion and happened a month or a year ago. But now it is blocking
this DICE thing from getting done <grumble>.