linux-kernel - Re: [PATCH v7 09/45] x86/sev: Save the negotiated GHCB version

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Message-ID: <5dea5250-d4fe-4f7b-91c1-a0460ed139b1@amd.com>
Date:   Tue, 7 Dec 2021 10:58:32 -0600
From:   Brijesh Singh <brijesh.singh@....com>
To:     Borislav Petkov <bp@...en8.de>, Tianyu Lan <ltykernel@...il.com>
Cc:     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,
        Michael Kelley <mikelley@...rosoft.com>,
        "Andrea Parri (Microsoft)" <parri.andrea@...il.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>,
        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 v7 09/45] x86/sev: Save the negotiated GHCB version



On 12/7/21 7:17 AM, Borislav Petkov wrote:
> On Tue, Dec 07, 2021 at 08:51:53PM +0800, Tianyu Lan wrote:
>> Hi Brijesh:
> 
> Do me a favor please and learn not to top-post on a public mailing list.
> Also, take the time to read Documentation/process/ before you send
> upstream patches and how to work with the community in general.
> 
>> We find this patch breaks AMD SEV support in the Hyper-V Isolation
>> VM. Hyper-V code also uses sev_es_ghcb_hv_call() to read or write msr
>> value. The sev_es_check_cpu_features() isn't called in the Hyper-V
>> code and so the ghcb_version is always 0.
> 
> If hyperv is going to expose hypervisor features, then it better report
> GHCB v2. If not, then I guess < 2 or 1 or so, depending on how this is
> defined.
> 
>> Could you add a new parameter ghcb_version for sev_es_ghcb_hv_call()
>> and then caller may input ghcb_version?
> 
> No, your hypervisor needs to adhere to the spec and report proper ghcb
> version. We won't be doing any accomodate-hyperv hacks.
> 


Agreed, the HyperV support need to negotiate the GHCB version before 
making those HC. In the current patch, the sev_es_negotiate_protocol() 
will save the ghcb_version in global variable and the saved value is 
used during the HC. Just make sure that initial HyperV support is 
adhering to the specification.

thanks