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

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Message-ID: <2a5cfbd0-865c-2a8b-b70b-f8f64aba5575@intel.com>
Date:   Fri, 10 Dec 2021 12:30:58 -0800
From:   Dave Hansen <dave.hansen@...el.com>
To:     Brijesh Singh <brijesh.singh@....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:     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 12/10/21 12:18 PM, Brijesh Singh wrote:
> On 12/10/21 1:12 PM, Dave Hansen wrote:
>> On 12/10/21 7:43 AM, Brijesh Singh wrote:
>>> +/* AMD SEV Confidential computing blob structure */
>>> +#define CC_BLOB_SEV_HDR_MAGIC	0x45444d41
>>> +struct cc_blob_sev_info {
>>> +	u32 magic;
>>> +	u16 version;
>>> +	u16 reserved;
>>> +	u64 secrets_phys;
>>> +	u32 secrets_len;
>>> +	u64 cpuid_phys;
>>> +	u32 cpuid_len;
>>> +};
>> This is an ABI structure rather than some purely kernel construct, right?
> 
> This is ABI between the guest BIOS and Guest OS. It is defined in the OVMF.
> 
> https://github.com/tianocore/edk2/blob/master/OvmfPkg/Include/Guid/ConfidentialComputingSevSnpBlob.h
> 
> SEV-SNP FW spec does not have it documented; it's up to the guest BIOS
> on how it wants to communicate the Secrets and CPUID page location to
> guest OS.

Well, no matter where it is defined, could we please make it a bit
easier for folks to find it in the future?

>> I searched through all of the specs to which you linked in the cover
>> letter.  I looked for "blob", "guid", the magic and part of the GUID
>> itself trying to find where this is defined to see if the struct is correct.
>>
>> I couldn't find anything.
>>
>> Where is the spec for this blob?  How large is it?  Did you mean to
>> leave a 4-byte hole after secrets_len and before cpuid_phys?
> Yes, the length is never going to be > 4GB.

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?