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

[Chao Gao]

On Thu, Jun 18, 2026 at 04:13:40PM +0800, Xu Yilun wrote:
>In addition to basic TDX functionalities, TDX module provides add-on
>features that can be progressively enabled as the kernel supports them.
>The kernel should explicitly configure these features at boot or
>post-update initialization time. Configuring an add-on feature, such as
>TDX Quoting, that uses extension SEAMCALLs is the prerequisite for
>initializing TDX module extensions. TDX Quoting is the target feature to
>enable but defer it for now until full kernel support is in place.
>
>TDX module extends TDH.SYS.CONFIG and TDH.SYS.UPDATE with new bitmap
>input parameters to specify which add-on features to configure. The
>bitmap uses the same definitions as TDX_FEATURES0.
>
>For runtime update, Linux applies a policy that no newer features should
>be added after update to avoid disrupting live TDX operations. To adhere
>to this, TDH.SYS.UPDATE must configure the same features as the
>TDH.SYS.CONFIG. Record the kernel required add-on feature bitmap in a
>global var so that both phases can use it.

Actually, we do not need another global variable here. tdx_features0 is cached
and is not updated across a runtime update, so the derived add-on feature
bitmap will be the same before and after the update.


> static __init int config_tdx_module(struct tdmr_info_list *tdmr_list,
> 				    u64 global_keyid)
> {
>+	u64 seamcall_fn = TDH_SYS_CONFIG_V0;
> 	struct tdx_module_args args = {};
> 	u64 *tdmr_pa_array;
> 	size_t array_sz;
>@@ -1032,7 +1042,15 @@ static __init int config_tdx_module(struct tdmr_info_list *tdmr_list,
> 	args.rcx = __pa(tdmr_pa_array);
> 	args.rdx = tdmr_list->nr_consumed_tdmrs;
> 	args.r8 = global_keyid;
>-	ret = seamcall_prerr(TDH_SYS_CONFIG, &args);
>+
>+	set_tdx_addon_features();
>+
>+	if (tdx_addon_feature0) {
>+		args.r9 = tdx_addon_feature0;

How about moving this r9 assignment out of the if block and placing it next to
'args.r8 = global_keyid;'? There is no need to guard it, because args.r9 will
be 0 when no add-on features are enabled, which is perfectly fine.

>+		seamcall_fn = TDH_SYS_CONFIG;
>+	}
>+
>+	ret = seamcall_prerr(seamcall_fn, &args);