linux-kernel - Re: [PATCH v4 11/19] x86/cpu: Print VMX flags in /proc/cpuinfo using VMX_FEATURES

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Date:   Thu, 12 Dec 2019 20:04:19 +0200
From:   Liran Alon <liran.alon@...cle.com>
To:     Jim Mattson <jmattson@...gle.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Borislav Petkov <bp@...en8.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        the arch/x86 maintainers <x86@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Joerg Roedel <joro@...tes.org>,
        Tony Luck <tony.luck@...el.com>,
        Tony W Wang-oc <TonyWWang-oc@...oxin.com>,
        Len Brown <lenb@...nel.org>, Shuah Khan <shuah@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        kvm list <kvm@...r.kernel.org>, linux-edac@...r.kernel.org,
        Linux PM list <linux-pm@...r.kernel.org>,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@...r.kernel.org>,
        Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
Subject: Re: [PATCH v4 11/19] x86/cpu: Print VMX flags in /proc/cpuinfo using
 VMX_FEATURES_*



> On 12 Dec 2019, at 19:57, Jim Mattson <jmattson@...gle.com> wrote:
> 
> On Thu, Dec 12, 2019 at 9:53 AM Liran Alon <liran.alon@...cle.com> wrote:
> 
>> Why should CPU VMX features be treated differently than standard CPUID deduced features?
> 
> Do we have the right Intel people on the recipient list to answer this
> question? Presumably, Intel felt that this information should be
> available in supervisor mode only.
> 
> Sean?

Good question. Probably because it just makes sense that Ring3 will never need to use
this info as all VMX instructions are privileged. i.e. Can only be executed in Ring0.

De-facto in KVM we have discovered this assumption to be problematic BTW,
as KVM created an interface to query VMX MSRs values to properly define the requested
vCPU model. :P (See kvm_get_msr_feature())