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

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Date:   Wed, 13 Oct 2021 23:37:44 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        Ingo Molnar <mingo@...hat.com>, 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>, 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

On Wed, Oct 13, 2021 at 11:25:35PM +0200, Thomas Gleixner wrote:
> So this ends up in doing:
> 
>    use();
>    init();
> 
> Can you spot what's wrong with that?
> 
> That's a clear violation of common sense and is simply not going to
> happen. Why? If you think about deep defensive programming then use()
> will look like this:
> 
> use()
> {
>         assert(initialized);
> }
> 
> which is not something made up. It's a fundamental principle of
> programming and some languages enforce that for very good reasons.
> 
> Just because it can be done in C is no justification.

Oh, I heartily agree.
 
> What's wrong with:
> 
> x86_64_start_kernel()
> 
>     tdx_early_init();
> 
>     copy_bootdata();
>     
>     tdx_late_init();
> 
> Absolutely nothing. It's clear, simple and well defined.

I like simple more than anyone, so sure, I'd prefer that a lot more.

And so the options parsing would need to happen early using, say,
cmdline_find_option() or so, like sme_enable() does.

Hmmm.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette