Re: [PATCH v3 4/4] virt: tdx-guest: Allocate Quote buffer dynamically

[Xiaoyao Li]

On 7/29/2026 8:29 PM, Peter Fang wrote:
> A new TDX module ABI reports the TD Quote size limit in a metadata
> field. This size used to be fixed at 128 KB.
> 
> The guest driver's Quote buffer is shared with the host VMM. The current
> fixed size may be too small for Quotes using schemes such as
> post-quantum cryptography (PQC), where larger certificate chains can
> increase the Quote size significantly.
> 
> Allocate the Quote buffer based on the reported limit. This avoids
> wasting memory on platforms that do not require larger Quotes. Older
> platforms fall back to the default 128 KB buffer.

I think we need to justify why using the value reported by TDX module
(i.e., QUOTE_MAX_SIZE) is safe.

>From "Intel TDX Module Extension for Quoting" spec,

  QUOTE_MAX_SIZE that specifies the maximum size of the buffer that must be
  allocated to contain the Intel TDX Quote received from Intel TDX Module.

So, TDX module only guarantees that QUOTE_MAX_SIZE is big enough to hold
the quote that is generated by the TDX module. But for the current tdx
guest driver, it doesn't know how host will generate the quote. Host can
generate the SGX-based quote and we need to justify the QUOTE_MAX_SIZE will
be enough for such case.