linux-kernel - Re: [PATCH v3 4/4] platform/x86: intel_tdx_attest: Add TDX Guest attestation interface driver

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Date:   Tue, 19 Apr 2022 07:24:43 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Sathyanarayanan Kuppuswamy 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        Kai Huang <kai.huang@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        Hans de Goede <hdegoede@...hat.com>,
        Mark Gross <mgross@...ux.intel.com>
Cc:     "H . Peter Anvin" <hpa@...or.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Tony Luck <tony.luck@...el.com>,
        Andi Kleen <ak@...ux.intel.com>, linux-kernel@...r.kernel.org,
        platform-driver-x86@...r.kernel.org
Subject: Re: [PATCH v3 4/4] platform/x86: intel_tdx_attest: Add TDX Guest
 attestation interface driver

On 4/19/22 07:19, Sathyanarayanan Kuppuswamy wrote:
> On 4/19/22 7:13 AM, Dave Hansen wrote:
>>> >From this perspective, I am not sure what's the value of having a
>>> dedicated
>>> INTEL_TDX_ATTESTATION Kconfig.  The attestation support code should
>>> be turned on
>>> unconditionally when CONFIG_INTEL_TDX_GUEST is on.  The code can also
>>> be just
>>> under arch/x86/coco/tdx/ I guess?
>> How much code are we talking about?  What's the difference in the size
>> of the binaries with this compiled in?
> 
> Current driver size is ~300 lines. It adds ~500 bytes to the kernel
> binary if it is built-in.

That doesn't sound like good use of a Kconfig option to me.  Just
explain in the cover letter:

	Any distribution enabling TDX is also expected to need
	attestation.  The compiled size is quite small (500 bytes).