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

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Date:   Mon, 18 Jan 2021 12:16:37 -0600
From:   Tom Lendacky <thomas.lendacky@....com>
To:     Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>
Cc:     "H. Peter Anvin" <hpa@...or.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, Brijesh Singh <brijesh.singh@....com>
Subject: Re: [PATCH] x86/sev: Add AMD_SEV_ES_GUEST Kconfig for including
 SEV-ES support

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
>