Re: [PATCH v4] x86/tdx: Dump TDX version During the TD Bootup

[Kuppuswamy Sathyanarayanan]

On 10/5/2023 11:28 PM, Yi Sun wrote:
> It is essential for TD users to be aware of the vendor and version of
> the current TDX. Additionally, they can reference the TDX version when
> reporting bugs or issues.
> 
> Furthermore, the applications or device drivers running in TD can achieve
> enhanced reliability and flexibility by following the TDX Module ABI
> specification, because there are significant differences between different
> versions of TDX, as mentioned in the "Intel® TDX Module Incompatibilities
> between v1.0 and v1.5" reference. Here are a few examples:
> 
> MSR Name		Index		Reason
> ----------------------------------------------
> IA32_UARCH_MISC_CTL	0x1B01		From v1.5
> IA32_ARCH_CAPABILITIES	0x010A		Changed in v1.5
> IA32_TSX_CTRL		0x0122		Changed in v1.5
> 
> CPUID Leaf	Sub-leaf	Reason
> ---------------------------------------
> 0x7		2		From v1.5
> 0x22		0		From v1.5
> 0x23		0~3		From v1.5
> 0x80000007	0		From v1.5
> 
> During TD initialization, the TDX version info can be obtained by calling
> TDG.SYS.RD. This will fetch the current version of TDX, including the major
> and minor version numbers and vendor ID.
> 
> The TDCALL TDG.SYS.RD originates from TDX version 1.5. If the error
> TDCALL_INVALID_OPERAND occurs, it should be treated as TDX version 1.0.
> 
> If the __tdcall_ret fails, expect a zero value for all tdx sys info.
> No additional error code is necessary to avoid introducing noise during
> the bootup.
> 
> Co-developed-by: Dongcheng Yan <dongcheng.yan@xxxxxxxxx>
> Signed-off-by: Dongcheng Yan <dongcheng.yan@xxxxxxxxx>
> Signed-off-by: Yi Sun <yi.sun@xxxxxxxxx>
> 
> diff --git a/arch/x86/coco/tdx/tdx.c b/arch/x86/coco/tdx/tdx.c
> index 3e6dbd2199cf..991f7dc695bd 100644
> --- a/arch/x86/coco/tdx/tdx.c
> +++ b/arch/x86/coco/tdx/tdx.c
> @@ -37,6 +37,24 @@
>  
>  #define TDREPORT_SUBTYPE_0	0
>  
> +/*
> + * TDX metadata base field id, used by TDCALL TDG.SYS.RD
> + * See TDX ABI Spec section 3.3.2.3 Global Metadata Fields
> + */
> +#define TDX_SYS_VENDOR_ID_FID		0x0800000200000000ULL
> +#define TDX_SYS_MINOR_FID		0x0800000100000003ULL
> +#define TDX_SYS_MAJOR_FID		0x0800000100000004ULL
> +#define TDX_VENDOR_INTEL		0x8086
> +
> +/*
> + * The global-scope metadata field via TDG.SYS.RD TDCALL
> + */

I think you can just say "struct used to cache TDX Module version info"

> +struct tdg_sys_info {
> +	u32 vendor_id;
> +	u16 major_version;
> +	u16 minor_version;
> +};
> +
>  /* Called from __tdx_hypercall() for unrecoverable failure */
>  noinstr void __noreturn __tdx_hypercall_failed(void)
>  {
> @@ -800,6 +818,60 @@ static bool tdx_enc_status_change_finish(unsigned long vaddr, int numpages,
>  	return true;
>  }
>  
> +/*
> + * Parse the tdx module version info from the global-scope metadata fields.
> + *
> + * Refer to Intel TDX Application Binary Interface (ABI) section
> + * "TDG.SYS.RD".
> + */

How about "Parse TDX Module version info from TDG.SYS.RD TDCALL"?

> +static void tdg_get_sysinfo(struct tdg_sys_info *td_sys)
> +{
> +	u64 ret;
> +	struct tdx_module_args args = {
> +		.rdx = TDX_SYS_VENDOR_ID_FID,
> +	};
> +
> +	if (!td_sys)
> +		return;

This check can be removed. It will never be NULL as per current usage.

> +
> +	memset(td_sys, 0, sizeof(struct tdg_sys_info));
> +
> +	/*
> +	 * TDCALL leaf TDX_SYS_RD
> +	 * Input Field Identifier via RDX and get the output via R8.
> +	 */

Since you are using a wrapper, I think you don't need to explain the register details here.

> +	ret = __tdcall_ret(TDX_SYS_RD, &args);
> +	/*
> +	 * The TDCALL TDG.SYS.RD originates from TDX version 1.5.
> +	 * Treat TDCALL_INVALID_OPERAND error as TDX version 1.0.
> +	 * If other errors occur, return with zero td_sys.
> +	 */
> +	if (TDCALL_RETURN_CODE(ret) == TDCALL_INVALID_OPERAND)
> +		goto version_1_0;
> +	else if (ret)
> +		return;
> +
> +	td_sys->vendor_id = (u32)args.r8;
> +
> +	args.rdx = TDX_SYS_MAJOR_FID;
> +	__tdcall_ret(TDX_SYS_RD, &args);

Why not check the return value?

> +
> +	td_sys->major_version = (u16)args.r8;
> +
> +	args.rdx = TDX_SYS_MINOR_FID;
> +	__tdcall_ret(TDX_SYS_RD, &args);

Same as above.

> +
> +	td_sys->minor_version = (u16)args.r8;

I recommend updating td_sys after executing both TDCALLs.

> +
> +	return;
> +
> +	/* TDX 1.0 does not have the TDCALL TDG.SYS.RD */
> +version_1_0:
> +	td_sys->vendor_id = TDX_VENDOR_INTEL;
> +	td_sys->major_version = 1;
> +	td_sys->minor_version = 0;
> +}
> +
>  void __init tdx_early_init(void)
>  {
>  	struct tdx_module_args args = {
> @@ -808,6 +880,7 @@ void __init tdx_early_init(void)
>  	};
>  	u64 cc_mask;
>  	u32 eax, sig[3];
> +	struct tdg_sys_info td_sys_info;
>  
>  	cpuid_count(TDX_CPUID_LEAF_ID, 0, &eax, &sig[0], &sig[2],  &sig[1]);
>  
> @@ -867,5 +940,9 @@ void __init tdx_early_init(void)
>  	 */
>  	x86_cpuinit.parallel_bringup = false;
>  
> -	pr_info("Guest detected\n");
> +	tdg_get_sysinfo(&td_sys_info);
> +
> +	pr_info("Guest detected. TDX version:%u.%u VendorID: %x\n",
> +		td_sys_info.major_version, td_sys_info.minor_version,
> +		td_sys_info.vendor_id);
>  }
> diff --git a/arch/x86/include/asm/shared/tdx.h b/arch/x86/include/asm/shared/tdx.h
> index f74695dea217..d326509832e6 100644
> --- a/arch/x86/include/asm/shared/tdx.h
> +++ b/arch/x86/include/asm/shared/tdx.h
> @@ -17,6 +17,7 @@
>  #define TDG_MR_REPORT			4
>  #define TDG_MEM_PAGE_ACCEPT		6
>  #define TDG_VM_WR			8
> +#define TDX_SYS_RD			11
>  
>  /* TDCS fields. To be used by TDG.VM.WR and TDG.VM.RD module calls */
>  #define TDCS_NOTIFY_ENABLES		0x9100000000000010

-- 
Sathyanarayanan Kuppuswamy
Linux Kernel Developer