linux-kernel - Re: [RFC PATCH 2/3] x86/cpufeatures: Combine word 11 and 12 into new scattered features word 11

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Message-ID: <20190614142139.GH2586@zn.tnic>
Date:   Fri, 14 Jun 2019 16:21:39 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Sean Christopherson <sean.j.christopherson@...el.com>
Cc:     Fenghua Yu <fenghua.yu@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, H Peter Anvin <hpa@...or.com>,
        Ravi V Shankar <ravi.v.shankar@...el.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        x86 <x86@...nel.org>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Subject: Re: [RFC PATCH 2/3] x86/cpufeatures: Combine word 11 and 12 into new
 scattered features word 11

On Fri, Jun 14, 2019 at 07:14:24AM -0700, Sean Christopherson wrote:
> This is wrong.  KVM isn't complaining about shuffling the order of feature
> words, it's complaining that code is trying to do a reverse CPUID lookup
> to a feature that isn't in the reverse_cpuid table.   Filtering out
> checks dynamically is just hiding bugs.

No no, reverse_cpuid is hardcoding our feature leafs. This is wrong as
we want to be able to change those. And reverse_cpuid[] should be able
to handle that.

KVM is complaining because he removed one leaf. He adds it later in
patch 3 as a Linux-defined leaf.

All that doesn't matter for KVM - if KVM wants to do reverse lookup,
then it should handle Linux-defined leafs just fine.

-- 
Regards/Gruss,
    Boris.

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