linux-kernel - Re: [PATCH v10 04/50] x86/cpufeatures: Add SEV-SNP CPU feature

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Message-ID: <9ac2311c-9ccc-4468-9b26-6cb0872e207f@redhat.com>
Date:   Wed, 13 Dec 2023 14:40:24 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     Michael Roth <michael.roth@....com>, kvm@...r.kernel.org,
        linux-coco@...ts.linux.dev, linux-mm@...ck.org,
        linux-crypto@...r.kernel.org, x86@...nel.org,
        linux-kernel@...r.kernel.org, tglx@...utronix.de, mingo@...hat.com,
        jroedel@...e.de, thomas.lendacky@....com, hpa@...or.com,
        ardb@...nel.org, seanjc@...gle.com, vkuznets@...hat.com,
        jmattson@...gle.com, luto@...nel.org, dave.hansen@...ux.intel.com,
        slp@...hat.com, pgonda@...gle.com, peterz@...radead.org,
        srinivas.pandruvada@...ux.intel.com, rientjes@...gle.com,
        dovmurik@...ux.ibm.com, tobin@....com, vbabka@...e.cz,
        kirill@...temov.name, ak@...ux.intel.com, tony.luck@...el.com,
        marcorr@...gle.com, sathyanarayanan.kuppuswamy@...ux.intel.com,
        alpergun@...gle.com, jarkko@...nel.org, ashish.kalra@....com,
        nikunj.dadhania@....com, pankaj.gupta@....com,
        liam.merwick@...cle.com, zhi.a.wang@...el.com,
        Brijesh Singh <brijesh.singh@....com>,
        Jarkko Sakkinen <jarkko@...fian.com>
Subject: Re: [PATCH v10 04/50] x86/cpufeatures: Add SEV-SNP CPU feature

On 12/13/23 14:36, Borislav Petkov wrote:
>> Sure, I only queued it because you gave Acked-by for 05/50 and this is an
>> obvious dependency.  I would like to get things in as they are ready
>> (whenever it makes sense), so if you want to include those two in the x86
>> tree for 6.8, that would work for me.
>
> It doesn't make sense to include them into 6.8 because the two alone are
> simply dead code in 6.8.

Why are they dead code?  X86_FEATURE_SEV_SNP is set automatically based 
on CPUID, therefore patch 5 is a performance improvement on all 
processors that support SEV-SNP.  This is independent of whether KVM can 
create SEV-SNP guests or not.

If this is wrong, there is a problem in the commit messages.

Paolo

> The plan is to put the x86 patches first in the next submission, I'll
> pick them up for 6.9 and then give you an immutable branch to apply the
> KVM bits ontop. This way it all goes together.