linux-kernel - Re: [PATCH] x86/msr: do not warn on writes to OC

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Date:   Wed, 21 Oct 2020 06:11:09 -0700
From:   Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>
To:     Dave Hansen <dave.hansen@...el.com>, Borislav Petkov <bp@...en8.de>
Cc:     Sultan Alsawaf <sultan@...neltoast.com>,
        "Jason A. Donenfeld" <Jason@...c4.com>,
        kitsunyan <kitsunyan@...mail.cc>,
        "Brown, Len" <len.brown@...el.com>, X86 ML <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH] x86/msr: do not warn on writes to OC_MAILBOX

On Tue, 2020-10-20 at 12:40 -0700, Dave Hansen wrote:
> On 10/20/20 11:40 AM, Srinivas Pandruvada wrote:
> > On Tue, 2020-10-20 at 19:47 +0200, Borislav Petkov wrote:
> > > On Tue, Oct 20, 2020 at 10:21:48AM -0700, Srinivas Pandruvada
> > > 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.
> > > Ok, is there a common *set* of values present on all models
> > Sorry, don't know.
> 
> So, the question is: Is Intel willing to document this on a
> sufficient
> number of models that folks can make a sane driver out of it?
> 
> Srinivas, that seems like a pretty sane thing for the community to
> ask.
>  We've got random folks poking at MSRs and we don't know whether
> they're
> nuts or not and whether we should spew warnings of disdain.  Seems
> like
> it would be in Intel's best interests to understand what users are
> doing
> with this MSR and to try to make sure they're not doing stuff which
> is
> too nutty, or at least give them the chance of avoiding warnings if
> they're being nice.
We are all for it. We have added several sysfs interfaces and adding
more.

> 
> Sounds like Borislav is willing to help give Intel's customers a
> nicer
> interface.  Mostly we from Intel would have to go dig out the docs
> for
> as many models as we can, and make sure we're allowed to talk about
> it
> publicly.
> 
That is the problem. There is no public document.

> I dunno.  Maybe we should try it for *one* model and see how it goes.
> Maybe start with the one we're already poking from inside the kernel.