linux-kernel - Re: [PATCH v2 2/3] virt: tdx-guest: Add Quote generation support

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Date:   Tue, 2 May 2023 15:27:53 -0700
From:   Chong Cai <chongc@...gle.com>
To:     Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
Cc:     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,
        Shuah Khan <shuah@...nel.org>,
        Jonathan Corbet <corbet@....net>,
        "H . Peter Anvin" <hpa@...or.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Tony Luck <tony.luck@...el.com>,
        Wander Lairson Costa <wander@...hat.com>,
        Erdem Aktas <erdemaktas@...gle.com>,
        Dionna Amalie Glaze <dionnaglaze@...gle.com>,
        Qinkun Bao <qinkun@...che.org>,
        Guorui Yu <GuoRui.Yu@...ux.alibaba.com>,
        Du Fan <fan.du@...el.com>, linux-kernel@...r.kernel.org,
        linux-kselftest@...r.kernel.org, linux-doc@...r.kernel.org
Subject: Re: [PATCH v2 2/3] virt: tdx-guest: Add Quote generation support

On Wed, Apr 12, 2023 at 8:42 PM Kuppuswamy Sathyanarayanan
<sathyanarayanan.kuppuswamy@...ux.intel.com> 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>".
>
> Add support for TDX_CMD_GET_QUOTE IOCTL to allow attestation agent
> submit GetQuote requests from the user space using GetQuote hypercall.
>
> Since GetQuote is an asynchronous request hypercall, VMM will use
> callback interrupt vector configured by SetupEventNotifyInterrupt
> hypercall to notify the guest about Quote generation completion or
> failure. So register an IRQ handler for it.
>
> GetQuote TDVMCALL requires TD guest pass a 4K aligned shared buffer
> with TDREPORT data as input, which is further used by the VMM to copy
> the TD Quote result after successful Quote generation. To create the
> shared buffer, allocate the required memory using alloc_pages() and
> mark it shared using set_memory_decrypted() in tdx_guest_init(). This
> buffer will be re-used for GetQuote requests in TDX_CMD_GET_QUOTE
> IOCTL handler.
>
> Although this method will reserve a fixed chunk of memory for
> GetQuote requests during the init time, it is preferable to the
> alternative choice of allocating/freeing the shared buffer in the
> TDX_CMD_GET_QUOTE IOCTL handler, which will damage the direct map.

Thanks Sathyanarayanan for the work. The patch looks good. Reserving a fixed
chunk of memory for GetQuote makes sense to me.

And just want to re-emphasize that the TDVMCALL approach is important for
many use cases that cannot depend on virtio/vsock.