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

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Message-Id: <7D245565-78D4-4587-AD5E-3D4E945D5A94@amacapital.net>
Date:   Fri, 19 Jun 2020 09:28:03 -0700
From:   Andy Lutomirski <luto@...capital.net>
To:     Borislav Petkov <bp@...en8.de>
Cc:     Richard Hughes <hughsient@...il.com>,
        Daniel Gutson <daniel@...ypsium.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>, Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        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 Jun 19, 2020, at 9:17 AM, Borislav Petkov <bp@...en8.de> wrote:
> 
> On Fri, Jun 19, 2020 at 08:48:47AM -0700, Andy Lutomirski wrote:
>> Boris, it wouldn’t be totally crazy for cpuinfo to learn to
>> distinguish between “your platform has this feature but Linux
>> isn’t using it” and “your platform doesn’t have this feature
>> in the first place”. And I suppose there’s this extra silly state
>> “your platform has this feature, but your firmware didn’t enable
>> it”. This would be a big job.
> 
> 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:
> 
> bit 0 - CPUID support
> bit 1 - BIOS enabled
> bit 2 - quirk applied
> bit 3 - microcode fixes present
> ...
> 
> and so on.
> 

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 we inevitably redo cpu features when Intel ships their hybrid Atom/Core machines.

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