linux-kernel - Re: [PATCH v7 04/12] x86/cpufeatures: Add TDX Guest CPU feature

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Date:   Thu, 23 Sep 2021 07:10:00 -0700
From:   "Kuppuswamy, Sathyanarayanan" 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, x86@...nel.org,
        Paolo Bonzini <pbonzini@...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 v7 04/12] x86/cpufeatures: Add TDX Guest CPU feature



On 9/23/21 3:02 AM, Borislav Petkov wrote:
> On Thu, Sep 16, 2021 at 11:35:42AM -0700, Kuppuswamy Sathyanarayanan wrote:
>> @@ -495,6 +496,8 @@ asmlinkage __visible void __init x86_64_start_kernel(char * real_mode_data)
>>   
>>   	copy_bootdata(__va(real_mode_data));
>>   
>> +	tdx_early_init();
>> +
> 
> | Changes since v4:
> |  * Moved tdx_early_init() below copy_bootdata() because of
> |    cmdline and IDT dependencies.
> 
> 
> What "cmdline and IDT dependencies"?
> 
> Without a comment explaining why that thing must be there in the boot
> order, you're adding more to the already fragile house of cards.
> 
> Explain please.

Initially, tdx_early_init() was added between kasan_early_init() and
idt_setup_early_handler() in x86_64_start_kernel(). But I found that
we have requirement to parse command line params in future
changes to tdx_early_init() (not from the patches in this series). Since
command line pointer is getting initialized in copy_bootdata(), I want
move the tdx_early_init() call below it. Instead of moving the initialization
order in future, I thought to move it appropriate place in the initial
patch. Regarding IDT dependency, #VE handling will have a dependency on
it (so it is better to initialize it before tdx_early_init()).

> 

-- 
Sathyanarayanan Kuppuswamy
Linux Kernel Developer