linux-kernel - Re: [PATCH v8 5/5] x86/tdx: Add Quote generation support

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Date:   Thu, 21 Jul 2022 10:02:05 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Sathyanarayanan Kuppuswamy 
        <sathyanarayanan.kuppuswamy@...ux.intel.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
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>,
        Kai Huang <kai.huang@...el.com>,
        Wander Lairson Costa <wander@...hat.com>,
        Isaku Yamahata <isaku.yamahata@...il.com>,
        marcelo.cerri@...onical.com, tim.gardner@...onical.com,
        khalid.elmously@...onical.com, philip.cox@...onical.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v8 5/5] x86/tdx: Add Quote generation support

On 7/21/22 09:54, Sathyanarayanan Kuppuswamy wrote:
> 
> On 7/21/22 9:49 AM, Dave Hansen wrote:
>> On 7/21/22 09:42, Sathyanarayanan Kuppuswamy wrote:
>>> On 7/21/22 9:08 AM, Dave Hansen wrote:
>>>> On 6/8/22 19:52, Kuppuswamy Sathyanarayanan wrote:
>>>>> For shared buffer allocation, alternatives like using the DMA API is
>>>>> also considered. Although it simpler to use, it is not preferred because
>>>>> dma_alloc_*() APIs require a valid bus device as argument, which would
>>>>> need converting the attestation driver into a platform device driver.
>>>>> This is unnecessary, and since the attestation driver does not do real
>>>>> DMA, there is no need to use real DMA APIs.
>>>> Let's actually try to walk through the requirements for the memory
>>>> allocation here.
>>>>
>>>>  1. The guest kernel needs to allocate some guest physical memory
>>>>     for the attestation data buffer
>>> Physically contiguous memory.
>> Remind me how large the quote structures are.
> It depends on the attestation service. In addition to TDREPORT (1K size),
> during quote generation, additional data can be included in the signed
> quote. So the spec allows variable length. User agent will communicate with
> attestation service to identify the appropriate buffer length. Our test
> uses 8K buffers

What is this "additional data"?  Is that "REPORTDATA" from the TDX
module spec?

	"Additional REPORTDATA, a 64-byte value, is provided by the
	guest TD to be included in the TDG.MR.REPORT."