linux-kernel - Re: [PATCH v4 1/6] x86: KVM: Advertise CMPccXADD CPUID to user space

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Message-ID: <6d7fae50-ef3c-dc1e-336c-691095007117@intel.com>
Date:   Mon, 21 Nov 2022 07:29:04 -0800
From:   Dave Hansen <dave.hansen@...el.com>
To:     Jiaxi Chen <jiaxi.chen@...ux.intel.com>
Cc:     kvm@...r.kernel.org, tglx@...utronix.de, mingo@...hat.com,
        bp@...en8.de, dave.hansen@...ux.intel.com, x86@...nel.org,
        hpa@...or.com, seanjc@...gle.com, pbonzini@...hat.com,
        ndesaulniers@...gle.com, alexandre.belloni@...tlin.com,
        peterz@...radead.org, jpoimboe@...nel.org,
        chang.seok.bae@...el.com, pawan.kumar.gupta@...ux.intel.com,
        babu.moger@....com, jmattson@...gle.com, sandipan.das@....com,
        tony.luck@...el.com, sathyanarayanan.kuppuswamy@...ux.intel.com,
        fenghua.yu@...el.com, keescook@...omium.org, nathan@...nel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 1/6] x86: KVM: Advertise CMPccXADD CPUID to user space

On 11/21/22 06:46, Jiaxi Chen wrote:
> Features which has been enabled in kernel usually should be added to
> /proc/cpuinfo.

Features that the kernel *itself* is actually using always get in there.
 Things like "smep".

But, things that the kernel "enables" but that only get used by
userspace don't generally show up in /proc/cpuinfo.

KVM is kinda a weird case.  The kernel is making the feature available
to guests, but it's not _using_ it in any meaningful way.  To me, this
seems much more akin to the features that are just available to
userspace than something that the kernel is truly using.

Also, these feature names are just long and ugly, and the "flags" line
is already a human-*un*readable mess.  I think we should just leave them
out.