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

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Message-ID: <261b8dc3-eb78-1c24-48f7-de6505e14c76@linux.intel.com>
Date:   Mon, 9 May 2022 17:17:12 -0700
From:   Sathyanarayanan Kuppuswamy 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
To:     Kai Huang <kai.huang@...el.com>,
        "Kirill A. Shutemov" <kirill@...temov.name>
Cc:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Dave Hansen <dave.hansen@...el.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 4:54 PM, Kai Huang wrote:
> And I suggested before, we can allocate a default size buffer (i.e. 4 pages),
> which is large enough to cover all requests for now, during driver
> initialization.  This avoids IOCTL time conversion.  We should still have code
> in the IOCTL to check the request buffer size and when it is larger than the
> default, the old should be freed a larger one should be allocated.  But for now
> this code path will never happen.
> 
> Btw above is based on assumption that we don't support concurrent IOCTLs.  This
> version Sathya somehow changed to support concurrent IOCTLs but this was a
> surprise as I thought we somehow agreed we don't need to support this.

Yes. Initially, I did not want to add this support to keep the code
simple. But recent changes (to handle cases like, cleanup the VMM
owned page after user prematurely ends the current request, and to
support VMAP model) already made the code complicated. With current
framework changes, since it is easy to extend the code to support
concurrent GetQuote requests, I have just enabled this support.


> 
> Anyway, now I don't have strong opinion here.  To me alloc_pages() +
> set_memory_decrypted() is also fine (seems AMD is using this anyway).   Will let
> Dave to decide.

-- 
Sathyanarayanan Kuppuswamy
Linux Kernel Developer