Re: [PATCH v2 03/17] x86/virt/tdx: Detect if the extensions initialization is required

[Xiaoyao Li]

On 6/18/2026 4:13 PM, Xu Yilun wrote:
> TDX module extensions support extension SEAMCALLs that are preemptible
> and resumable, unlike normal SEAMCALLs that run to completion while
> monopolizing the CPU. 

This is not true. There are some normal (non-extension) SEAMCALLs also 
are preemptible and resumable. For example,

- TDH.PHYMEM.CACHE.WB
- TDH.SYS.DISABLE
- TDH.MEM.SEPT.ADD with version 1

(There might be more. I didn't check all.)

> This allows for higher-level API constructions,
> so better supports some add-on features that implement higher order
> security protocols.

I think we don't need to explain this? Just that some add-on features 
require the functionalities of TDX module extensions is enough?

> Add infrastructure to initialize TDX module extensions. Introduce the
> initial step of this process by detecting if the extensions are required
> by checking:
>
>    1. If the extensions are supported via TDX_FEATURES0_EXT.
>    2. If any TDX add-on feature needs the extensions via a boolean
>       metadata field ext_required.
>
> Currently all metadata fields are read at the very beginning of basic
> TDX initialization and stored in a global var. However, ext_required is
> only valid after the add-on feature configuration, making it
> incompatible with the existing metadata reading method.
>
> To resolve this lifetime conflict, add a dedicated runtime metadata
> reading interface for the extensions, call it when the extensions
> initialization starts, and leave the field out of the global var. In
> this way, there is no confusion of when the metadata should be read.
>
> Signed-off-by: Xu Yilun <yilun.xu@xxxxxxxxxxxxxxx>
> ---
>   arch/x86/include/asm/tdx.h                  |  1 +
>   arch/x86/include/asm/tdx_global_metadata.h  |  4 ++++
>   arch/x86/virt/vmx/tdx/tdx.c                 | 25 +++++++++++++++++++++
>   arch/x86/virt/vmx/tdx/tdx_global_metadata.c | 14 ++++++++++++
>   4 files changed, 44 insertions(+)
>
> diff --git a/arch/x86/include/asm/tdx.h b/arch/x86/include/asm/tdx.h
> index e5a9cf656c07..5fbf89d5317c 100644
> --- a/arch/x86/include/asm/tdx.h
> +++ b/arch/x86/include/asm/tdx.h
> @@ -35,6 +35,7 @@
>   /* Bit definitions of TDX_FEATURES0 metadata field */
>   #define TDX_FEATURES0_TD_PRESERVING	BIT_ULL(1)
>   #define TDX_FEATURES0_NO_RBP_MOD	BIT_ULL(18)
> +#define TDX_FEATURES0_EXT		BIT_ULL(39)
>   
>   #ifndef __ASSEMBLER__
>   
> diff --git a/arch/x86/include/asm/tdx_global_metadata.h b/arch/x86/include/asm/tdx_global_metadata.h
> index 41150d546589..83fc657a438e 100644
> --- a/arch/x86/include/asm/tdx_global_metadata.h
> +++ b/arch/x86/include/asm/tdx_global_metadata.h
> @@ -52,4 +52,8 @@ struct tdx_sys_info {
>   	struct tdx_sys_info_td_conf td_conf;
>   };
>   
> +struct tdx_sys_info_ext {
> +	bool ext_required;
> +};
> +
>   #endif
> diff --git a/arch/x86/virt/vmx/tdx/tdx.c b/arch/x86/virt/vmx/tdx/tdx.c
> index 92305b5ea90d..6f3596f11d25 100644
> --- a/arch/x86/virt/vmx/tdx/tdx.c
> +++ b/arch/x86/virt/vmx/tdx/tdx.c
> @@ -1166,6 +1166,27 @@ static __init int init_tdmrs(struct tdmr_info_list *tdmr_list)
>   	return 0;
>   }
>   
> +static __init int init_tdx_module_extensions(void)
> +{
> +	struct tdx_sys_info_ext sysinfo_ext;
> +	int ret;
> +
> +	if (!(tdx_sysinfo.features.tdx_features0 & TDX_FEATURES0_EXT))
> +		return 0;
> +
> +	ret = get_tdx_sys_info_ext(&sysinfo_ext);
> +	if (ret)
> +		return ret;
> +
> +	/* Skip if no feature requires TDX module extensions. */
> +	if (!sysinfo_ext.ext_required)
> +		return 0;

There was the discussion around it in [1]. I agree with the point to 
make kernel code simple. But it requires change/clarification from TDX 
spec, right? So will TDX spec change?

If so, you would need to mention it somewhere.

[1] 
https://lore.kernel.org/all/9c00b87b7b69470ad1e7b1d2788414002b9a1c77.camel@xxxxxxxxx/

> +	/* TODO: add the extensions enabling steps here */
> +
> +	return 0;
> +}
> +
>   static __init int init_tdx_module(void)
>   {
>   	int ret;
> @@ -1220,6 +1241,10 @@ static __init int init_tdx_module(void)
>   	if (ret)
>   		goto err_reset_pamts;
>   
> +	ret = init_tdx_module_extensions();
> +	if (ret)
> +		goto err_reset_pamts;
> +
>   	pr_info("%lu KB allocated for PAMT\n", tdmrs_count_pamt_kb(&tdx_tdmr_list));
>   
>   out_put_tdxmem:
> diff --git a/arch/x86/virt/vmx/tdx/tdx_global_metadata.c b/arch/x86/virt/vmx/tdx/tdx_global_metadata.c
> index e49c300f23d4..b9e1c011a990 100644
> --- a/arch/x86/virt/vmx/tdx/tdx_global_metadata.c
> +++ b/arch/x86/virt/vmx/tdx/tdx_global_metadata.c
> @@ -131,3 +131,17 @@ static __init int get_tdx_sys_info(struct tdx_sys_info *sysinfo)
>   
>   	return ret;
>   }
> +
> +static __init int get_tdx_sys_info_ext(struct tdx_sys_info_ext *sysinfo_ext)
> +{
> +	int ret;
> +	u64 val;
> +
> +	ret = read_sys_metadata_field(0x3100000000000001, &val);
> +	if (ret)
> +		return ret;
> +
> +	sysinfo_ext->ext_required = val;
> +
> +	return 0;
> +}