linux-kernel - Re: [PATCH Part1 v5 33/38] x86/sev: Provide support for SNP guest request NAEs

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Date:   Fri, 27 Aug 2021 15:31:54 -0500
From:   Tom Lendacky <thomas.lendacky@....com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     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,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Joerg Roedel <jroedel@...e.de>,
        "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>,
        Wanpeng Li <wanpengli@...cent.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>,
        Michael Roth <michael.roth@....com>,
        Vlastimil Babka <vbabka@...e.cz>,
        "Kirill A . Shutemov" <kirill@...temov.name>,
        Andi Kleen <ak@...ux.intel.com>, tony.luck@...el.com,
        marcorr@...gle.com, sathyanarayanan.kuppuswamy@...ux.intel.com
Subject: Re: [PATCH Part1 v5 33/38] x86/sev: Provide support for SNP guest
 request NAEs

On 8/27/21 3:17 PM, Borislav Petkov wrote:
> On Fri, Aug 27, 2021 at 02:57:11PM -0500, Tom Lendacky wrote:
>> The main thing about this is that it is an error code from the HV on
>> extended guest requests. The HV error code sits in the high-order 32-bits of
>> the SW_EXIT_INFO_2 field. So defining it either way seems a bit confusing.
>> To me, the value should just be 1ULL and then it should be shifted when
>> assigning it to the SW_EXIT_INFO_2.
> 
> Err, that's from the GHCB spec:
> 
> "The hypervisor must validate that the guest has supplied enough pages
> 
> ...
> 
> certificate data in the RBX register and set the SW_EXITINFO2 field to
> 0x0000000100000000."
> 
> So if you wanna do the above, you need to fix the spec first. I'd say.
> 
> :-)

See the NAE Event table that documents "State from Hypervisor" where it 
says the upper 32-bits (63:32) will contain the return code from the 
hypervisor.

In the case you quoted, that specific situation is documented to return a 
hypervisor return code of 1 (since the hypervisor return code occupies 
bits 63:32). The hypervisor is free to return other values, that need not 
be documented in spec, if it encounters other types of unforeseeable errors.

Thanks,
Tom

>