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

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Message-ID: <20231213134945.GFZXm2eTkd+IfdsjVE@fat_crate.local>
Date:   Wed, 13 Dec 2023 14:49:45 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Paolo Bonzini <pbonzini@...hat.com>
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 Wed, Dec 13, 2023 at 02:40:24PM +0100, Paolo Bonzini wrote:
> 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.

No, it is not. This CPUID bit means:

"RMP table can be enabled to protect memory even from hypervisor."

Without the SNP host patches, it is dead code.

And regardless, arch/x86/kvm/ patches go through the kvm tree. The rest
of arch/x86/ through the tip tree. We've been over this a bunch of times
already.

If you don't agree with this split, let's discuss it offlist with all
tip and kvm maintainers, reach an agreement who picks up what and to put
an end to this nonsense.

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette