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

[Tony Lindgren <tony.lindgren@linux.intel.com>]

On Thu, Sep 03, 2026 at 02:21:35PM +0800, Xiaoyao Li wrote:
> 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.

And can we assume the TDX module provided size does not change after init
with a TDX module update?