Re: [PATCH] x86/sev: Add AMD_SEV_ES_GUEST Kconfig for including SEV-ES support

[Tom Lendacky <thomas.lendacky@amd.com>]

On 1/18/21 12:03 PM, Paolo Bonzini wrote:
> On 16/01/21 06:40, Tom Lendacky wrote:
>>
>>> Introduce a new Kconfig, AMD_SEV_ES_GUEST, to control the inclusion of
>>> support for running as an SEV-ES guest.  Pivoting on AMD_MEM_ENCRYPT for
>>> guest SEV-ES support is undesirable for host-only kernel builds as
>>> AMD_MEM_ENCRYPT is also required to enable KVM/host support for SEV and
>>> SEV-ES.
>>
>> I believe only KVM_AMD_SEV is required to enable the KVM support to run 
>> SEV and SEV-ES guests. The AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT setting is 
>> only used to determine whether to enable the KVM SEV/SEV-ES support by 
>> default on module load.
> 
> Right:
> 
>          if (IS_ENABLED(CONFIG_KVM_AMD_SEV) && sev) {
>                  sev_hardware_setup();
>          } else {
>                  sev = false;
>                  sev_es = false;
>          }
> 
> I removed the addition to "config AMD_MEM_ENCRYPT_ from Sean's patch, but 
> (despite merging it not once but twice) I don't really like the hidden 
> dependency on AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT and thus AMD_MEM_ENCRYPT.  
> Is there any reason to not always enable sev/sev_es by default?

I don't remember where the AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT suggestion 
originally came from. I thought it was from review feedback on the 
original SEV patches, but can't find anything about it. @Brijesh might 
remember.

But I see no reason not to enable them by default.

Thanks,
Tom

> 
> Paolo
>