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Message-ID: <d5b54f8c-2e03-4ac8-8b8a-605c7f0f601b@linux.intel.com>
Date:   Wed, 14 Sep 2022 17:30:45 -0700
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Subject: Re: [PATCH v13 1/3] x86/tdx: Add TDX Guest attestation interface
 driver
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To:     Dave Hansen <dave.hansen@intel.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        Dave Hansen <dave.hansen@linux.intel.com>, x86@kernel.org,
        Shuah Khan <shuah@kernel.org>
Cc:     "H . Peter Anvin" <hpa@zytor.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
        Tony Luck <tony.luck@intel.com>,
        Andi Kleen <ak@linux.intel.com>,
        Kai Huang <kai.huang@intel.com>,
        Wander Lairson Costa <wander@redhat.com>,
        Isaku Yamahata <isaku.yamahata@gmail.com>,
        marcelo.cerri@canonical.com, tim.gardner@canonical.com,
        khalid.elmously@canonical.com, philip.cox@canonical.com,
        linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org,
        linux-doc@vger.kernel.org
References: <20220909192708.1113126-1-sathyanarayanan.kuppuswamy@linux.intel.com>
 <20220909192708.1113126-2-sathyanarayanan.kuppuswamy@linux.intel.com>
 <7c3cc265-869b-b2fc-43f2-d2cbd0bc142c@intel.com>
 <1182ef92-cae3-b7c1-8339-8e8bfa48f2e3@linux.intel.com>
 <d238f235-5623-d152-c0d3-2ef851f88473@intel.com>
From:   Sathyanarayanan Kuppuswamy 
        <sathyanarayanan.kuppuswamy@linux.intel.com>
In-Reply-To: <d238f235-5623-d152-c0d3-2ef851f88473@intel.com>
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On 9/14/22 9:12 AM, Dave Hansen wrote:
> On 9/14/22 08:36, Sathyanarayanan Kuppuswamy wrote:
>> When we initially submitted the attestation patches, virt/coco folder
>> was not created. I initially kept this driver in platform/x86/, but
>> later moved to arch/x86/coco based on the review comments in v4. There
>> was a discussion about the need for a new config and the location of
>> the driver. The outcome of that discussion is, since this is not a
>> traditional driver, but a basic TDX feature, we don't need a special
>> config and the code can be maintained in the arch/x86/coco folder.
> 
> Could you please include the following in this set somewhere:
> 
> "The code to do the SEV analog of this TDX functionality is in
> ___insert_path_here____.   This code is different from that because
> ______reason______ so it is instead placed in ____other_path____."
> 
> ?

I have also included info about why we don't use a separate config
option for it.

The code for the SEV equivalent of this TDX attestation functionality
can be found in drivers/virt/coco/sev-guest/. It is implemented as a
platform module driver, and it can be enabled using the CONFIG_SEV_GUEST
config option. However, in the case of TDX, it is implemented as a
built-in driver in the arch/x86/coco/tdx/tdx.c because of the following
reasons:

1. Attestation is expected to be needed by all distributions that support
   TDX. Therefore, using a separate configuration option is not necessary.
   With TDX support, it can be enabled by default, and a built-in driver
   model will work better in this use case.
2. Since it is not a conventional device driver and the code is very simple,
   creating an individual driver for it may be an overkill.

-- 
Sathyanarayanan Kuppuswamy
Linux Kernel Developer