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

[dan.j.williams]

Kuppuswamy Sathyanarayanan wrote:
> 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.

That is good feedback. I would rather not restart the timer on the
linux-next exposure with a rebase to add that. I think in this case it
is sufficient that the commit has a link back to this discussion:

Link: https://patch.msgid.link/20260211001712.1531955-4-sathyanarayanan.kuppuswamy@xxxxxxxxxxxxxxx

However, when the the patch to add the link to the documentation for the
CBOR Web Token schema is ready, do take the opportunity to also add a
patch commenting about the order-5 allocation risk to
GET_QUOTE_BUF_SIZE.

Later, when / if these objects start to get into order-10+ allocations
for PQC etc, a scatter-gather mechanism will need to be considered.