Re: [PATCH v3 2/4] x86/tdx: Add tdx_hcall_get_quote() API support

[Kai Huang <kai.huang@intel.com>]

On Mon, 2022-04-18 at 22:28 -0700, Sathyanarayanan Kuppuswamy wrote:
> 
> On 4/18/22 9:40 PM, Kai Huang wrote:
> > > Please check the latest 1.0 specification (updated on Feb 2022). It has
> > > details about R13 register.
> > Thanks.  So it seems GHCI 1.0 has also been updated and it is consistent with
> > GHCI 1.5 now.  In this case, why do we still assume 8K shared memory?  Are you
> > going to update the driver?
> > 
> 
> Since the GetQuote spec only requires memory in 4K alignment, we just
> went with 8k constant allocation. Since existing users does not
> require more than 8k, it works. But I agree that this needs to be
> changed.

Quote format can be vendor specific, so there's no guarantee 3rd party won't
have a Quote larger than 8k.

> 
> In next version, I will change the driver to choose the allocation size
> based on user space request. Since this change would require us to do
> the memory allocation in IOCTL routine (instead of init code), it will
> make it slower. But I think this is negligible compared to time it takes
> for Quote request. So it should be fine.
> 
> > 

Yes attestation request should never be something that is very frequent, thus
should never be in a performance critical path.