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

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Date:   Thu, 15 Jul 2021 19:56:32 +0800
From:   Xiaoyao Li <xiaoyao.li@...el.com>
To:     Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Andy Lutomirski <luto@...nel.org>
Cc:     Peter H Anvin <hpa@...or.com>, Dave Hansen <dave.hansen@...el.com>,
        Tony Luck <tony.luck@...el.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Kirill Shutemov <kirill.shutemov@...ux.intel.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Kuppuswamy Sathyanarayanan <knsathya@...nel.org>,
        x86@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 03/11] x86/cpufeatures: Add TDX Guest CPU feature

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");
> +}
>