Re: [PATCH v3 0/4] tdx-guest: Make Quote buffer size dynamic

[Peter Fang <peter.fang@intel.com>]

On Wed, Aug 12, 2026 at 09:02:21AM -0700, Edgecombe, Rick P wrote:
> On Wed, 2026-08-12 at 07:08 -0700, Sean Christopherson wrote:
> > >   |Normal quote    |Migration quote |Report size|Quote size|uAPI location  |
> > > -|----------------|----------------|-----------|----------|---------------|
> > > 1|Platform scoped |Platform scoped |Grows      |Grows     |TDX host driver|
> > 
> > With my KVM hat on, this option looks very attractive.
> > 
> > And with the caveat that I'm most definitely not an attestation expert, from a
> > separate of concerns perspective, IMO it seems like the report should contain
> > the TD-specific information while the quote just wraps that information in
> > platform-specific goo.
> > 
> > In other words, to me, TD-scoped quotes feel like a hack that was thrown in to
> > avoid having to modify the guest because y'all didn't plan ahead.
> 
> Caveman crypto person here too. It seems scattered and makes me similarly
> suspicious about some lack of planning. But I kind of came to a different
> conclusion on what went wrong.
> 
> It seems to me that from the overall solution level, the report should never
> have had the details in it. It should just be some nonce or some type of thing
> that can tie the guest request to the quote that it ends up getting
> back. Doesn't it seem weird to get a bunch of details from the TDX module, then
> pass them from the guest to host KVM to host userspace then back to the TDX
> module... which already had all those details?

Yeah this has been a source of much debate internally. I feel that the
directions boil down to: is now a good opportunity to design something
that's more future looking (like can scale better wrt future attestation
needs) or is it better to keep the old SGX design a little longer...

> 
> My understanding was that the original SGX attestation was a complicator of the
> design of this stuff. Because I'm not sure that SGX had all those details about
> the TD. In fact I can't see how it could have. Is that right Peter? So it needs
> them all to be passed in. All the extra validations etc of this shuffling is
> TDX's problems to deal with, but for Linux, it would be at least a lot less
> confusing if there was not two things that have the TD details in them.

Yep this is correct IMO. Basically the report has lots of old SGX
baggage.

> 
> That said, from KVM POV, (1) kicks the attestation out of KVM. I see the
> benefit. But a TD quote is a TD scoped operation in concept. To me at least.