linux-kernel - Re: [PATCH v8 5/5] x86/tdx: Add Quote generation support

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Message-ID: <1fdecc17-8f4f-fceb-8da0-4a21ca0d58be@intel.com>
Date:   Thu, 21 Jul 2022 11:52:24 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Isaku Yamahata <isaku.yamahata@...il.com>
Cc:     Sathyanarayanan Kuppuswamy 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        "H . Peter Anvin" <hpa@...or.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Tony Luck <tony.luck@...el.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Kai Huang <kai.huang@...el.com>,
        Wander Lairson Costa <wander@...hat.com>,
        marcelo.cerri@...onical.com, tim.gardner@...onical.com,
        khalid.elmously@...onical.com, philip.cox@...onical.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v8 5/5] x86/tdx: Add Quote generation support

On 7/21/22 11:42, Isaku Yamahata wrote:
> Regarding to the size of quote, there is no hard limit because it's for future
> usage.  But here is a rough idea about it.
> 
> - 4KB(1 page) can accommodate TDREPORT that is defined right now.
> - 128KB is too small for foreseen use cases.
> - 1MB is too big. big enough for future.

Again, we're off in the weeds.

How does the VMM know how much to read/write?  I have a theory: the spec
says that R12 is:

	"Shared 4KB GPA as input – the memory contains a
	TDREPORT_STRUCT."

That's *A* 4KB GPA.  The maximum is one 4KB page.  That's the only thing
that makes sense because there's no length in the ABI anywhere.

What am I missing?