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 10:18:02 -0800
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Borislav Petkov <bp@...en8.de>,
        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 Thu, Dec 12, 2019 at 03:13:45PM +0100, Paolo Bonzini 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

Tying into the consistency comment below, any objection to always prefixing
"ept" for relevant controls instead of following the SDM?  Specifically,
that would yield ept_mode_based_exec and ept_spp

> > 
> > 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?

I'll go with tsc_offset.

> > virtual_tpr		-> vtpr
> 
> Do we need this?  It's usually included together with flexpriority.
> 
> > virt_apic_accesses	-> vapic

Using v<feature> across the board makes sense to keep things consistent,
i.e. vnmi, vtpr, vapic, etc...

Anyone have thoughts on how to shorten "APIC-register virtualization"
without colliding with vapic or apicv?  I currently have apic_reg_virt,
which is a bit wordy.  apic_regv isn't awful, but I don't love it.

The other control that will be awkard is "Virtual Interrupt Delivery".
vint_delivery?

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

I prefer unrestricted_guest, a bare unrestricted just makes me wonder
"unrestricted what?".   But I can live with "unrestricted" if that's the
consensus.

> 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.

IMO there's value in printing features that are not 1:1 with module params.

I also think it makes sense to print features of interest even if KVM
doesn't (yet) support the feature, e.g. to allow a user/developer to check
if they can use/test a KVM build with support for a new feature without
having to build and install the new kernel.

> 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. :-)