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Date:   Wed, 21 Oct 2020 15:24:33 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Cc:     Borislav Petkov <bp@alien8.de>,
        Sultan Alsawaf <sultan@kerneltoast.com>,
        "Jason A. Donenfeld" <Jason@zx2c4.com>,
        kitsunyan <kitsunyan@airmail.cc>,
        "Brown, Len" <len.brown@intel.com>, X86 ML <x86@kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [PATCH] x86/msr: do not warn on writes to OC_MAILBOX
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On Tue, Oct 20, 2020 at 10:21:48AM -0700, Srinivas Pandruvada wrote:
> On Mon, 2020-10-19 at 19:15 +0200, Borislav Petkov wrote:

> These command id are model specific. There is no guarantee that even
> meaning changes. So I don't think we should write any code in kernel
> which can't stick.
> 
> 
> > In any case, my point is that we could have a sysfs interface for
> > those userspace-suppliable values like the undervolt value at
> > [31:21],
> > dunno if the index can be inferred by the kernel automatically or
> > enumerated and the commands we should issue ourselves depending on
> > the
> > functionality, etc.

Why not have a full undervolt driver. That is, don't expose OC_MAILBOX
_at_all_, but have a model specific driver that provides undervolt
capabilities.

Someone is now maintaining this thing in userspace, might as well do it
as a kernel driver and keep all the icky bits inside.