Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Content-Type: text/plain;
        charset=utf-8
Mime-Version: 1.0 (Mac OS X Mail 11.1 \(3445.4.7\))
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: <52dd758d-a590-52a6-4248-22d6852b75cd@redhat.com>
Date:   Thu, 12 Dec 2019 19:52:55 +0200
Cc:     Sean Christopherson <sean.j.christopherson@intel.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>
Content-Transfer-Encoding: quoted-printable
Message-Id: <DA429131-7A4C-4B74-A020-6CE7622ED2F8@oracle.com>
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>
 <52dd758d-a590-52a6-4248-22d6852b75cd@redhat.com>
To:     Paolo Bonzini <pbonzini@redhat.com>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk


> On 12 Dec 2019, at 19:47, Paolo Bonzini <pbonzini@redhat.com> wrote:
>=20
> On 12/12/19 18:43, Sean Christopherson wrote:
>> 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.
>=20
> There are tools such as vmxcap.  It is part of QEMU, but I wouldn't =
mind
> moving it into the kernel tree.
>=20
> Paolo
>=20

True. But it relies on /dev/msr0 (exposed from msr kernel module) to be =
able to read any host arbitrary MSR.
It=E2=80=99s much more elegant to just report CPU VMX features in a =
/proc/cpuinfo pseudo-file and don=E2=80=99t require strong privileges.
Why should CPU VMX features be treated differently than standard CPUID =
deduced features?
CPU SVM features are also present in /proc/cpuinfo today (Because they =
are deduced from CPUID leafs). So it should be similar.

-Liran=