Re: [PATCH 2/2] virt: tdx-guest: Allocate Quote buffer dynamically

[Peter Fang]

On Fri, Jul 10, 2026 at 11:32:55AM +0800, Binbin Wu wrote:
> On 6/12/2026 7:08 PM, Peter Fang wrote:
> > From: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@xxxxxxxxxxxxxxx>
> > 
> > The TDX attestation driver currently uses a fixed 128 KB Quote buffer
> > shared with the host VMM. This may be too small for Quotes using schemes
> > such as post-quantum cryptography (PQC), where certificate chains can
> > increase the Quote size to several megabytes.
> 
> Nit:
> I think the description here should be more accurate.
> "Several megabytes" colloquially implies sizes that could easily exceed 4 MB.
> And it's a slight contradiction VS the 4MB limitation below.

Good point. I'll make this clearer.

> 
> > 
> > Allocate the Quote buffer based on the size reported by the TDX module
> > instead of always reserving a fixed-size buffer. This avoids wasting
> > memory on platforms that do not require larger Quotes. Older platforms
> > fall back to the default 128 KB buffer.
> > 
> > Because the Quote buffer must be physically contiguous, its size is
> > bound by the buddy allocator's maximum page order (4 MB), which should
> > be sufficient for current attestation needs.
> > 
> > struct tdx_quote_buf has a trailing flexible array, so use offsetof()
> > instead of sizeof() to calculate the header size.
> > 
> > Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@xxxxxxxxxxxxxxx>
> > Assisted-by: Claude:claude-opus-4-7
> > Assisted-by: GitHub Copilot:gpt-5.4
> 
> Same issue as pointed by Kiryl in the first patch.

There have been discussions about this recently [1]. I think perhaps I
should drop the "Assisted-by" tags since I did not use AI to write the
actual code.

[1] https://lore.kernel.org/linux-coco/akxHbKbMyF7PZ0Av@xxxxxxxxxx/

> 
> > Signed-off-by: Peter Fang <peter.fang@xxxxxxxxx>
> 
> Also the use of struct_size_t() instead of offsetof().

Yep.

> 
> Otherwise looks okay to me:
> 
> Reviewed-by: Binbin Wu <binbin.wu@xxxxxxxxxxxxxxx>

Thanks for the review Binbin!