Re: [PATCH v3] x86/sev: Add SEV-SNP guest feature negotiation support

[Nikunj A. Dadhania]

On 03/01/23 01:12, Borislav Petkov wrote:
> On Mon, Jan 02, 2023 at 08:50:23PM +0530, Nikunj A. Dadhania wrote:
>> I think the "why" part depends on the user. Whether or not the user needs a
>> certain feature enabled for the confidential guest.
>>
>> If the cloud provider(hypervisor) enables the feature on user request, the
>> guest terminates with GHCB_SNP_FEAT_NOT_IMPLEMENTED when guest kernel does
>> have corresponding code/implementation.
> 
> I think you mean "does not have" here.

Yes, that is correct.

> 
> In any case, I think this whole handling of SEV features could go both ways:
> 
> * Cloud provider could say: we've enabled features X, Y and Z and if the guest
> doesn't have support for them, then it would fail booting.
> 
> There would optimally be some text sowewhere in the cloud provider documentation
> stating why those features are enabled and thus required to be supported by the
> guest.
> 
> * Guest owner could require a minimal subset of features which must be present
> in the HV in order to even boot on that HV.
> 
> Of course, I'm only speculating here. How it ends up really playing out in
> reality we will have to see...
>