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 19:03:17 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Tom Lendacky <thomas.lendacky@....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 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?

Paolo