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

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Message-ID: <e4c0a191-ee26-9768-cbf5-c1d9782b1586@linux.intel.com>
Date:   Wed, 13 Oct 2021 15:28:51 -0700
From:   Sathyanarayanan Kuppuswamy 
        <sathyanarayanan.kuppuwamy@...ux.intel.com>
To:     Borislav Petkov <bp@...en8.de>,
        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 10/13/21 2:37 PM, Borislav Petkov wrote:
> 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.

Since in tdx_early_init() all we are going to do is to initialize
"tdx_guest_detected" using cpuid call, shall we name it
tdx_guest_cpuid_init()? (similar to sme_enable call in AMD)

>
> Hmmm.
>
-- 
Sathyanarayanan Kuppuswamy
Linux Kernel Developer