linux-kernel - Re: [PATCH 0/2] KVM: x86: Propagate AMD-specific IBRS bits to guests

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Date:   Mon, 6 Mar 2023 22:25:29 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Sean Christopherson <seanjc@...gle.com>,
        Borislav Petkov <bp@...en8.de>
Cc:     Takahiro Itazuri <itazur@...zon.com>, dave.hansen@...ux.intel.com,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        mingo@...hat.com, tglx@...utronix.de, x86@...nel.org,
        zulinx86@...il.com
Subject: Re: [PATCH 0/2] KVM: x86: Propagate AMD-specific IBRS bits to guests

On 3/6/23 22:16, Sean Christopherson wrote:
>> Not harmless - cpufeatures.h should contain flags which the kernel uses
>> and not*every*  CPUID bit out there.
>
> I thought that the consensus was that adding unused-by-the-kernel flags to
> cpufeatures.h is ok so long as the feature is hidden from /proc/cpuinfo and the
> kernel already dedicates a word to the CPUID leaf?
Yeah, I understand adding no new CPUID leaf just for KVM, but you don't 
gain anything really from not having X86_FEATURE_* defines.

Paolo