Re: [PATCH] x86/Hyper-V: Add SEV negotiate protocol support in Isolation VM

[Tianyu Lan <ltykernel@gmail.com>]

On 5/10/2022 6:48 AM, Borislav Petkov wrote:
> On Thu, May 05, 2022 at 09:15:02AM -0400, Tianyu Lan wrote:
>> From: Tianyu Lan <Tianyu.Lan@microsoft.com>
>>
>> Hyper-V Isolation VM code uses sev_es_ghcb_hv_call() to read/write MSR
>> via GHCB page. The SEV-ES guest should negotiate GHCB version before
>> reading/writing MSR via GHCB page.
> 
> Why is that?
> 
>> Expose sev_es_negotiate_protocol() and sev_es_terminate() from AMD SEV
>> code
> 
> Yeah, you keep wanting to expose random SEV-specific code and when we
> go and change it in the future, you'll come complaining that we broke
> hyperv.
> 
> I think it might be a lot better if you implement your own functions:
> for example, looking at sev_es_negotiate_protocol() - it uses only
> primitives which you can use because, well, VMGEXIT() is simply a
> wrapper around the asm insn and sev_es_wr_ghcb_msr() is simply writing
> into the MSR.
> 
> Ditto for sev_es_terminate().
> 
> And sev_es_ghcb_hv_call() too, for that matter. You can define your own.
> 
> IOW, you're much better off using those primitives and creating your own
> functions than picking out random SEV-functions and then us breaking
> your isolation VM stuff.
> 

OK. I got it. Thanks for your suggestion.