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From:   Richard Hughes <hughsient@gmail.com>
Date:   Fri, 19 Jun 2020 14:50:39 +0100
Message-ID: <CAD2FfiFRqwYGB50KK=aA0sU6uCALYneoyD=V4EfOsk-Ex=C+xg@mail.gmail.com>
Subject: Re: [PATCH] Ability to read the MKTME status from userspace
To:     Borislav Petkov <bp@alien8.de>
Cc:     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>
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On Fri, 19 Jun 2020 at 14:44, Borislav Petkov <bp@alien8.de> wrote:
> Yes, this is what I'm proposing with clearing the flag in /proc/cpuinfo.
> The needed information is there:
> 1. TME in CPUID
> 2. TME *not* in /proc/cpuinfo

No, it's not a boolean at all. If the platform disable is a BIOS
configuration we don't know if TME isn't available because the CPU
doesn't support it or because the firmware has disabled it. In the
latter case, a firmware update or firmware configuration change might
actually enable it. If the user installs a CPU with TME support and
then we tell the user "your system doesn't support TME" then we're
going to have some very confused users unless we can differentiate the
two cases.

> Along with proper ABI definition, design,
> documentation and all that belongs to a proper interface with userspace.

I don't think Daniels patch was a "final version" and I'm sure
follow-ups can add this kind of thing. At the moment it's just people
telling him "you don't need this" when as a potential consumer I'm
saying we really do.

Richard.