linux-kernel - Re: [PATCH v1 3/3] virt: tdx-guest: Increase Quote buffer size to 128KB

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Message-ID: <6983882c-2c00-42f4-924b-5fb3619840be@linux.intel.com>
Date: Wed, 11 Feb 2026 10:40:21 -0800
From: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>
To: Kiryl Shutsemau <kas@...nel.org>
Cc: Dan Williams <dan.j.williams@...el.com>,
 Dave Hansen <dave.hansen@...ux.intel.com>,
 Rick Edgecombe <rick.p.edgecombe@...el.com>, x86@...nel.org,
 linux-kernel@...r.kernel.org, linux-coco@...ts.linux.dev
Subject: Re: [PATCH v1 3/3] virt: tdx-guest: Increase Quote buffer size to
 128KB

Hi Kiryl,

Thanks for the review!

On 2/11/2026 3:17 AM, Kiryl Shutsemau wrote:
> On Tue, Feb 10, 2026 at 04:17:12PM -0800, Kuppuswamy Sathyanarayanan wrote:
>> Intel platforms are transitioning from traditional SGX-based
>> attestation toward DICE-based attestation as part of a broader move
>> toward open and standardized attestation models. DICE enables layered
>> and extensible attestation, where evidence is accumulated across
>> multiple boot stages.
>>
>> With SGX-based attestation, Quote sizes are typically under 8KB, as the
>> payload consists primarily of Quote data and a small certificate bundle.
>> Existing TDX guest code sizes the Quote buffer accordingly.
>>
>> DICE-based attestation produces significantly larger Quotes due to the
>> inclusion of evidence (certificate chains) from multiple boot layers.
>> The cumulative Quote size can reach approximately 100KB.
>>
>> Increase GET_QUOTE_BUF_SIZE to 128KB to ensure sufficient buffer
>> capacity for DICE-based Quote payloads.
> 
> It worth noting that it requires guest physically-contiguous memory.
> 
> Single order-5 allocation is not that bad as long as the driver
> initialized during the boot.

Good point! We can add following to the commit log:

The Quote buffer requires guest physically-contiguous memory and is
allocated once during driver initialization at boot time, where an
order-5 allocation (128KB) is expected to succeed reliably.

> 

-- 
Sathyanarayanan Kuppuswamy
Linux Kernel Developer