linux-kernel - Re: [PATCH v8 27/40] x86/boot: Add Confidential Computing type to setup

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Date:   Mon, 13 Dec 2021 09:55:27 -0600
From:   Brijesh Singh <brijesh.singh@....com>
To:     Dave Hansen <dave.hansen@...el.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        linux-efi@...r.kernel.org, platform-driver-x86@...r.kernel.org,
        linux-coco@...ts.linux.dev, linux-mm@...ck.org
Cc:     brijesh.singh@....com, Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Joerg Roedel <jroedel@...e.de>,
        Tom Lendacky <thomas.lendacky@....com>,
        "H. Peter Anvin" <hpa@...or.com>, Ard Biesheuvel <ardb@...nel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Jim Mattson <jmattson@...gle.com>,
        Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Sergio Lopez <slp@...hat.com>, Peter Gonda <pgonda@...gle.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        David Rientjes <rientjes@...gle.com>,
        Dov Murik <dovmurik@...ux.ibm.com>,
        Tobin Feldman-Fitzthum <tobin@....com>,
        Borislav Petkov <bp@...en8.de>,
        Michael Roth <michael.roth@....com>,
        Vlastimil Babka <vbabka@...e.cz>,
        "Kirill A . Shutemov" <kirill@...temov.name>,
        Andi Kleen <ak@...ux.intel.com>,
        "Dr . David Alan Gilbert" <dgilbert@...hat.com>,
        tony.luck@...el.com, marcorr@...gle.com,
        sathyanarayanan.kuppuswamy@...ux.intel.com
Subject: Re: [PATCH v8 27/40] x86/boot: Add Confidential Computing type to
 setup_data



On 12/13/21 9:08 AM, Dave Hansen wrote:
> On 12/13/21 6:49 AM, Brijesh Singh wrote:
>>> I was more concerned that this structure could change sizes if it were
>>> compiled on 32-bit versus 64-bit code.  For kernel ABIs, we try not to
>>> do that.
>>>
>>> Is this somehow OK when talking to firmware?  Or can a 32-bit OS and
>>> 64-bit firmware never interact?
>>
>> For SNP, both the firmware and OS need to be 64-bit. IIRC, both the
>> Linux and OVMF do not enable the memory encryption for the 32-bit.
> 
> Could you please make the structure's size invariant?  

Ack. I will make the required changes.

That's great if
> there's no problem in today's implementation, but it's best no to leave
> little land mines like this around.  Let's say someone copies your code
> as an example of something that interacts with a firmware table a few
> years or months down the road.
>