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

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Date:   Wed, 23 Nov 2022 14:33:32 +0800
From:   Jiaxi Chen <jiaxi.chen@...ux.intel.com>
To:     Dave Hansen <dave.hansen@...el.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 11/21/2022 11:29 PM, Dave Hansen wrote:
> 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.

True and agree. As for these cpuids are not truly used by kernel except
for advertising to kvm userspace, we can hide them in /proc/cpuinfo by
overriding their name with "".

-- 
Regards,
Jiaxi