linux-kernel - Re: [PATCH v7 02/10] x86/tdx: Add early_is_tdx

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Date:   Sun, 17 Oct 2021 21:28:38 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, Paolo Bonzini <pbonzini@...hat.com>,
        David Hildenbrand <david@...hat.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        "H . Peter Anvin" <hpa@...or.com>
Cc:     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>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v7 02/10] x86/tdx: Add early_is_tdx_guest() interface

On Tue, Oct 05 2021 at 13:41, Kuppuswamy Sathyanarayanan wrote:
> +
> +#define TDX_CPUID_LEAF_ID                       0x21
> +
> +static int tdx_guest = -1;
> +
> +static inline bool early_cpuid_has_tdx_guest(void)
> +{
> +	u32 eax = TDX_CPUID_LEAF_ID, sig[3] = {0};
> +
> +	if (cpuid_eax(0) < TDX_CPUID_LEAF_ID)
> +		return false;
> +
> +	cpuid_count(TDX_CPUID_LEAF_ID, 0, &eax, &sig[0], &sig[2], &sig[1]);
> +
> +	return !memcmp("IntelTDX    ", sig, 12);
> +}
> +
> +bool early_is_tdx_guest(void)
> +{
> +	if (tdx_guest < 0)
> +		tdx_guest = early_cpuid_has_tdx_guest();
> +
> +	return !!tdx_guest;
> +}

Sigh.