linux-kernel - Re: [PATCH v5 3/3] x86/tdx: Add Quote generation support

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Date:   Mon, 9 May 2022 07:14:20 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     "Kirill A. Shutemov" <kirill@...temov.name>,
        Kai Huang <kai.huang@...el.com>
Cc:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        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>, Tony Luck <tony.luck@...el.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Wander Lairson Costa <wander@...hat.com>,
        Isaku Yamahata <isaku.yamahata@...il.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 v5 3/3] x86/tdx: Add Quote generation support

On 5/9/22 05:09, Kirill A. Shutemov wrote:
> Private->Shared conversion is destructive. You have to split SEPT, flush
> TLB. Backward conversion even more costly.
> 
> Rule of thumb is avoid conversion where possible. DMA API is there for
> you.

Kirill, I understand that the DMA API is a quick fix today.  But is it
_really_ the right long-term interface?

There will surely come a time when TDX I/O devices won't be using fixed
bounce buffers.  What will the quote generation code do then?  How will
we know to come back around and fix this up?

Does SEV or the s390 ultravisor need anything like this?