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Subject: Re: [PATCH v7 09/45] x86/sev: Save the negotiated GHCB version
To:     Borislav Petkov <bp@alien8.de>, Tianyu Lan <ltykernel@gmail.com>
References: <20211110220731.2396491-1-brijesh.singh@amd.com>
 <20211110220731.2396491-10-brijesh.singh@amd.com>
 <5b1c348a-fc26-e257-7bc2-82d1326de321@gmail.com> <Ya9e7fDxj6WiomqI@zn.tnic>
From:   Brijesh Singh <brijesh.singh@amd.com>
Message-ID: <5dea5250-d4fe-4f7b-91c1-a0460ed139b1@amd.com>
Date:   Tue, 7 Dec 2021 10:58:32 -0600
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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