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From:   Andy Lutomirski <luto@amacapital.net>
Mime-Version: 1.0 (1.0)
Subject: Re: [PATCH] Ability to read the MKTME status from userspace
Date:   Fri, 19 Jun 2020 09:28:03 -0700
Message-Id: <7D245565-78D4-4587-AD5E-3D4E945D5A94@amacapital.net>
References: <20200619161752.GG32683@zn.tnic>
Cc:     Richard Hughes <hughsient@gmail.com>,
        Daniel Gutson <daniel@eclypsium.com>,
        Dave Hansen <dave.hansen@intel.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, x86@kernel.org,
        "H. Peter Anvin" <hpa@zytor.com>, Arnd Bergmann <arnd@arndb.de>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Peter Zijlstra <peterz@infradead.org>,
        "David S. Miller" <davem@davemloft.net>,
        Rob Herring <robh@kernel.org>, Tony Luck <tony.luck@intel.com>,
        Rahul Tanwar <rahul.tanwar@linux.intel.com>,
        Xiaoyao Li <xiaoyao.li@intel.com>,
        Sean Christopherson <sean.j.christopherson@intel.com>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        linux-kernel <linux-kernel@vger.kernel.org>
In-Reply-To: <20200619161752.GG32683@zn.tnic>
To:     Borislav Petkov <bp@alien8.de>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk


> On Jun 19, 2020, at 9:17 AM, Borislav Petkov <bp@alien8.de> wrote:
>=20
> =EF=BB=BFOn Fri, Jun 19, 2020 at 08:48:47AM -0700, Andy Lutomirski wrote:
>> Boris, it wouldn=E2=80=99t be totally crazy for cpuinfo to learn to
>> distinguish between =E2=80=9Cyour platform has this feature but Linux
>> isn=E2=80=99t using it=E2=80=9D and =E2=80=9Cyour platform doesn=E2=80=99=
t have this feature
>> in the first place=E2=80=9D. And I suppose there=E2=80=99s this extra sil=
ly state
>> =E2=80=9Cyour platform has this feature, but your firmware didn=E2=80=99t=
 enable
>> it=E2=80=9D. This would be a big job.
>=20
> Well, I believe all the kernel can do is supply bits of information -
> just like MSRs - and depending on the settings of those bits, userspace
> can decide what the situation is. For example:
>=20
> bit 0 - CPUID support
> bit 1 - BIOS enabled
> bit 2 - quirk applied
> bit 3 - microcode fixes present
> ...
>=20
> and so on.
>=20

Indeed.

> It needs a proper definition though and userspace to say, yes, we want
> that and that is useful for us.

Maybe the right approach is to just keep this kind of use in mind for when w=
e inevitably redo cpu features when Intel ships their hybrid Atom/Core machi=
nes.

>=20
> Where it ends up is then beside the point - /proc/cpuinfo,
> /sys/devices/system/cpu, whatever...
>=20
> --=20
> Regards/Gruss,
>    Boris.
>=20
> https://people.kernel.org/tglx/notes-about-netiquette