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Date:   Fri, 22 Jul 2022 12:05:24 -0700
From:   Isaku Yamahata <isaku.yamahata@gmail.com>
To:     Dave Hansen <dave.hansen@intel.com>
Cc:     Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@linux.intel.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        Dave Hansen <dave.hansen@linux.intel.com>, x86@kernel.org,
        "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>,
        Kai Huang <kai.huang@intel.com>,
        Wander Lairson Costa <wander@redhat.com>,
        Isaku Yamahata <isaku.yamahata@gmail.com>,
        marcelo.cerri@canonical.com, tim.gardner@canonical.com,
        khalid.elmously@canonical.com, philip.cox@canonical.com,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH v8 5/5] x86/tdx: Add Quote generation support
Message-ID: <20220722190524.GA3299911@ls.amr.corp.intel.com>
References: <20220609025220.2615197-1-sathyanarayanan.kuppuswamy@linux.intel.com>
 <20220609025220.2615197-6-sathyanarayanan.kuppuswamy@linux.intel.com>
 <403cfccb-7fff-ab0b-8ebd-e5b04e631571@intel.com>
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On Thu, Jul 21, 2022 at 05:27:08PM -0700,
Dave Hansen <dave.hansen@intel.com> wrote:

> On 6/8/22 19:52, Kuppuswamy Sathyanarayanan wrote:
> > In TDX guest, the second stage in attestation process is to send the
> > TDREPORT to QE/QGS to generate the TD Quote. For platforms that does
> > not support communication channels like vsock or TCP/IP, implement
> > support to get TD Quote using hypercall. GetQuote hypercall can be used
> > by the TD guest to request VMM facilitate the Quote generation via
> > QE/QGS. More details about GetQuote hypercall can be found in TDX
> > Guest-Host Communication Interface (GHCI) for Intel TDX 1.0, section
> > titled "TDG.VP.VMCALL<GetQuote>.
> 
> So, the quote portion of this is basically a bidirectional blob sender.
>  It's to send a blob between guest userspace to host userspace.
> 
> Do we *REALLY* need specific driver functionality for this?  For
> instance, is there no existing virtio device that can send blobs back
> and forth?

It's virtio-vsock.  If virtio-vsock is available, the communication works.
However, some users would like to disable virtio-vsock on their environment for
some reasons.  Even virtio at all.  Especially for confidential computing use
case.  It's their choice.  It can't be assumed that virtio is available.

The goal is VMM-agnostic (but TDX-specific) interface for that.
-- 
Isaku Yamahata <isaku.yamahata@gmail.com>