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

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Date:   Tue, 19 Jan 2021 08:23:20 -0800
From:   Sean Christopherson <seanjc@...gle.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, x86@...nel.org,
        Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        "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, Tom Lendacky <thomas.lendacky@....com>,
        Brijesh Singh <brijesh.singh@....com>
Subject: Re: [PATCH] x86/sev: Add AMD_SEV_ES_GUEST Kconfig for including
 SEV-ES support

On Mon, Jan 18, 2021, Borislav Petkov wrote:
> On Mon, Jan 18, 2021 at 09:32:07PM +0100, Paolo Bonzini wrote:
> > I think it makes sense because AMD_SEV_ES_GUEST's #VC handling is quite a
> > bit of code that you may not want or need.
> 
> Quite a bit of code which ends up practically enabled on the majority of
> distros.
> 
> And it ain't about savings of whopping KiBs. And yet another Kconfig symbol
> in our gazillion Kconfig symbols space means ugly ifdeffery and paying
> attention to randconfig builds.
> 
> For tailored configs you simply disable AMD_MEM_ENCRYPT on !AMD hw and
> all done.

It was the AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT dependency that tripped me up.  To
get KVM to enable SEV/SEV-ES by default, that needs to be enabled, which in turn
requires AMD_MEM_ENCRYPT=y.  I didn't realize that there isn't actually a
dependency on AMD_MEM_ENCRYPT=y

> So I don't see the point for this.

Agreed, I'll send a KVM patch to remove the AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT
dependency.