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Date:   Thu, 21 Jul 2022 11:52:24 -0700
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Subject: Re: [PATCH v8 5/5] x86/tdx: Add Quote generation support
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To:     Isaku Yamahata <isaku.yamahata@gmail.com>
Cc:     Sathyanarayanan Kuppuswamy 
        <sathyanarayanan.kuppuswamy@linux.intel.com>,
        Thomas Gleixner <tglx@linutronix.de>,
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        "H . Peter Anvin" <hpa@zytor.com>,
        "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
        Tony Luck <tony.luck@intel.com>,
        Andi Kleen <ak@linux.intel.com>,
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        khalid.elmously@canonical.com, philip.cox@canonical.com,
        linux-kernel@vger.kernel.org
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From:   Dave Hansen <dave.hansen@intel.com>
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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?