linux-kernel - Re: [PATCH v10 03/11] x86/cpufeatures: Add TDX Guest CPU feature

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Date:   Wed, 13 Oct 2021 23:35:49 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Sathyanarayanan Kuppuswamy 
        <sathyanarayanan.kuppuwamy@...ux.intel.com>,
        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>,
        Juergen Gross <jgross@...e.com>, Deep Shah <sdeep@...are.com>,
        VMware Inc <pv-drivers@...are.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.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>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v10 03/11] x86/cpufeatures: Add TDX Guest CPU feature

Sathyanarayanan,

On Wed, Oct 13 2021 at 14:05, Sathyanarayanan Kuppuswamy wrote:
> On 10/13/21 1:44 PM, Thomas Gleixner wrote:
>> tdx_early_init() is invoked from x86_64_start_kernel() very early in the
>> boot process __before__ is_tdx_guest() is invoked.
>>
>> So why on earth is it requried to keep those conditionals and cpuid()
>> muck around after init?
>
> is_tdx_guest() is also used by cc_platform_has() API. Please check
> the following patch [1]. cc_platform_has() will be called much earlier
> than x86_64_start_kernel() (like __startup_64() [2]).

That's just fundamentally wrong as I pointed out to Borislav already.

AMD has done it the right way.

__startup_64()
  sme_enable()

  x86_64_start_kernel()
    sme_early_init()
    copy_bootdata()
    ...

It's not that hard and we are not going to make this fundamentally
different just because Intel.

Thanks,

        tglx