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Subject: Re: [PATCH v4 11/19] x86/cpu: Print VMX flags in /proc/cpuinfo using
 VMX_FEATURES_*
From:   Liran Alon <liran.alon@oracle.com>
In-Reply-To: <20191212174357.GE3163@linux.intel.com>
Date:   Thu, 12 Dec 2019 19:47:51 +0200
Cc:     Paolo Bonzini <pbonzini@redhat.com>,
        Borislav Petkov <bp@alien8.de>,
        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>,
        =?utf-8?B?UmFkaW0gS3LEjW3DocWZ?= <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>
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References: <20191128014016.4389-1-sean.j.christopherson@intel.com>
 <20191128014016.4389-12-sean.j.christopherson@intel.com>
 <20191212122646.GE4991@zn.tnic>
 <d0b21e7e-69f5-09f9-3e1c-14d49fa42b9f@redhat.com>
 <4A24DE75-4E68-4EC6-B3F3-4ACB0EE82BF0@oracle.com>
 <17c6569e-d0af-539c-6d63-f4c07367d8d1@redhat.com>
 <20191212174357.GE3163@linux.intel.com>
To:     Sean Christopherson <sean.j.christopherson@intel.com>
Sender: linux-kernel-owner@vger.kernel.org
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> On 12 Dec 2019, at 19:43, Sean Christopherson =
<sean.j.christopherson@intel.com> wrote:
>=20
> On Thu, Dec 12, 2019 at 04:57:10PM +0100, Paolo Bonzini wrote:
>> On 12/12/19 16:52, Liran Alon wrote:
>>>>> 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.=20
>>> APICv currently represents in KVM terminology the combination of
>>> APIC-register virtualization, virtual-interrupt-delivery and
>>> posted-interrupts (See cpu_has_vmx_apicv()).
>>>=20
>>> In fact, the coupling of =E2=80=9Cenable_apicv=E2=80=9D 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.
>>>=20
>>> Even you got confused as virtualize-apic-access is not part of =
KVM=E2=80=99s
>>> APICv terminology but rather it=E2=80=99s 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.
>>=20
>> Right, I got confused with APIC-register virtualization.  Virtualize
>> APIC accesses is another one I wouldn't bother putting in =
/proc/cpuinfo,
>> since it's usually present together with flexpriority.
>=20
> Key word being "usually".  My intent in printing out partially =
redundant
> flags was to help users debug/understand why the combined feature =
isn't
> supported.  E.g. userspace can already easily (relatively speaking) =
query
> flexpriority support via =
/sys/module/kvm_intel/parameters/flexpriority.
> But if that comes back "N", the user has no way to determine exactly =
why
> flexpriority is disabled.

+1 on that.

/proc/cpuinfo should just dump supported VMX features that kernel is =
aware of as exposed from CPU.
Without further processing.