Re: [PATCH v3 03/11] x86/cpufeatures: Add TDX Guest CPU feature

[Xiaoyao Li]

On 6/19/2021 6:57 AM, Kuppuswamy Sathyanarayanan wrote:
> Add CPU feature detection for Trusted Domain Extensions support. TDX
> feature adds capabilities to keep guest register state and memory
> isolated from hypervisor.
>
> For TDX guest platforms, executing CPUID(eax=0x21, ecx=0) will return
> following values in EAX, EBX, ECX and EDX.
>
> EAX:  Maximum sub-leaf number:  0
> EBX/EDX/ECX:  Vendor string:
>
> EBX =  "Inte"
> EDX =  "lTDX"
> ECX =  "    "
>
> So when above condition is true, set X86_FEATURE_TDX_GUEST feature cap
> bit.

...

> +static inline bool cpuid_has_tdx_guest(void)
> +{
> +	u32 eax, sig[3];
> +
> +	if (cpuid_eax(0) < TDX_CPUID_LEAF_ID)
> +		return false;
> +
> +	cpuid_count(TDX_CPUID_LEAF_ID, 0, &eax, &sig[0], &sig[1], &sig[2]);

As change log describes, EBX + EDX + ECX is "IntelTDX    ", not EBX + 
ECX + EDX. So it should be

	cpuid_count(TDX_CPUID_LEAF_ID, 0, &eax, &sig[0], &sig[2], &sig[1]);

Please also correct early_cpuid_has_tdx_guest()

> +
> +	return !memcmp("IntelTDX    ", sig, 12);
> +}
> +
> +void __init tdx_early_init(void)
> +{
> +	if (!cpuid_has_tdx_guest())
> +		return;
> +
> +	setup_force_cpu_cap(X86_FEATURE_TDX_GUEST);
> +
> +	pr_info("Guest initialized\n");
> +}