Re: [PATCH v4 11/19] x86/cpu: Print VMX flags in /proc/cpuinfo using VMX_FEATURES_*

From: Liran Alon <liran.alon@oracle.com>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: "Borislav Petkov" <bp@alien8.de>,
	"Sean Christopherson" <sean.j.christopherson@intel.com>,
	"Thomas Gleixner" <tglx@linutronix.de>,
	"Ingo Molnar" <mingo@redhat.com>,
	x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
	"Peter Zijlstra" <peterz@infradead.org>,
	"Arnaldo Carvalho de Melo" <acme@kernel.org>,
	"Mark Rutland" <mark.rutland@arm.com>,
	"Alexander Shishkin" <alexander.shishkin@linux.intel.com>,
	"Jiri Olsa" <jolsa@redhat.com>,
	"Namhyung Kim" <namhyung@kernel.org>,
	"Radim Krčmář" <rkrcmar@redhat.com>,
	"Vitaly Kuznetsov" <vkuznets@redhat.com>,
	"Wanpeng Li" <wanpengli@tencent.com>,
	"Jim Mattson" <jmattson@google.com>,
	"Joerg Roedel" <joro@8bytes.org>,
	"Tony Luck" <tony.luck@intel.com>,
	"Tony W Wang-oc" <TonyWWang-oc@zhaoxin.com>,
	"Len Brown" <lenb@kernel.org>, "Shuah Khan" <shuah@kernel.org>,
	linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
	linux-edac@vger.kernel.org, linux-pm@vger.kernel.org,
	linux-kselftest@vger.kernel.org,
	"Jarkko Sakkinen" <jarkko.sakkinen@linux.intel.com>
Subject: Re: [PATCH v4 11/19] x86/cpu: Print VMX flags in /proc/cpuinfo using VMX_FEATURES_*
Date: Thu, 12 Dec 2019 17:52:12 +0200
Message-ID: <4A24DE75-4E68-4EC6-B3F3-4ACB0EE82BF0@oracle.com> (raw)
In-Reply-To: <d0b21e7e-69f5-09f9-3e1c-14d49fa42b9f@redhat.com>

> On 12 Dec 2019, at 16:13, Paolo Bonzini <pbonzini@redhat.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. :-)
> 