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 17:52:12 +0200
From:   Liran Alon <liran.alon@...cle.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Borislav Petkov <bp@...en8.de>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, 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>,
        Jim Mattson <jmattson@...gle.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>,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        linux-edac@...r.kernel.org, linux-pm@...r.kernel.org,
        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 16:13, Paolo Bonzini <pbonzini@...hat.com> wrote:
> 
> On 12/12/19 13:26, Borislav Petkov wrote:
>> 
>> vmx flags       : virtual_nmis preemption_timer invvpid ept_x_only ept_ad ept_1gb flexpriority tsc_offsetting virtual_tpr mtf virt_apic_accesses ept vpid unrestricted_guest ple shadow_vmcs pml mode_based_ept_exec
>> 
>> virtual_nmis		-> vnmis
> 
> Even vnmi
> 
>> preemption_timer	-> preempt_tmr
> 
> I would prefer the full one here.
> 
>> flexpriority		-> flexprio
> 
> Full name?
> 
>> tsc_offsetting		-> tsc_ofs
> 
> tsc_offset?
> 
>> virtual_tpr		-> vtpr
> 
> Do we need this?  It's usually included together with flexpriority.
> 
>> virt_apic_accesses	-> vapic
> 
> apicv

Frankly, I dislike APICv terminology. I prefer to enumerate the various VMX features which are collectively called APICv by KVM.
APICv currently represents in KVM terminology the combination of APIC-register virtualization, virtual-interrupt-delivery and posted-interrupts (See cpu_has_vmx_apicv()).

In fact, the coupling of “enable_apicv” module parameter have made me multiple times to need to disable entire APICv features when there for example was only a bug in posted-interrupts.

Even you got confused as virtualize-apic-access is not part of KVM’s APICv terminology but rather it’s enablement depend on flexpriority_enabled (See cpu_need_virtualize_apic_accesses()). i.e. It can be used for faster intercept handling of accesses to guest xAPIC MMIO page.

> 
>> unrestricted_guest	-> unres_guest
> 
> Full? Or just unrestricted

I prefer unrestricted_guest.

> 
> In general I would stick to the same names as kvm_intel module
> parameters (sans "enable_" if applicable) and not even bother publishing
> the others.  Some features are either not used by KVM or available on
> all VMX processors.
> 
> Paolo
> 
>> and so on. Those are just my examples - I betcha the SDM is more
>> creative here with abbreviations. But you guys are going to grep for
>> them. If it were me, I'd save on typing. :-)
>