linux-kernel - Re: [PATCH] Ability to read the MKTME status from userspace

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Message-ID: <CAD2FfiGT5bsb0sd2k8NGNmShvW_q3UV9YXgn-EwxBCJjx6PSTw@mail.gmail.com>
Date:   Fri, 19 Jun 2020 20:58:23 +0100
From:   Richard Hughes <hughsient@...il.com>
To:     Andy Lutomirski <luto@...nel.org>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Borislav Petkov <bp@...en8.de>,
        Daniel Gutson <daniel@...ypsium.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, X86 ML <x86@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>, Arnd Bergmann <arnd@...db.de>,
        Peter Zijlstra <peterz@...radead.org>,
        "David S. Miller" <davem@...emloft.net>,
        Rob Herring <robh@...nel.org>, Tony Luck <tony.luck@...el.com>,
        Rahul Tanwar <rahul.tanwar@...ux.intel.com>,
        Xiaoyao Li <xiaoyao.li@...el.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] Ability to read the MKTME status from userspace

On Fri, 19 Jun 2020 at 20:41, Andy Lutomirski <luto@...nel.org> wrote:
> I don't object in principle to Linux giving userspace more visibility
> into what's going on, but I'm not convinced that adding a new
> must-support-for-a-long-time interface that only solves 5% of your
> problem is worth it.

At the moment the only visibility we have is "the CPU supports TME"
and "the kernel printed a message in the journal". The sysfs/procfs
file read allows us to notify the admin if the firmware is
deliberately disabling TME for some reason, without resorting to
`grep` on dmesg. I don't think perfect should be the enemy of the
good.

Richard.