linux-kernel - Re: [RFC] #MC mess

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Date:   Wed, 19 Feb 2020 16:05:07 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Andy Lutomirski <luto@...nel.org>, Borislav Petkov <bp@...en8.de>,
        Tony Luck <tony.luck@...el.com>, x86-ml <x86@...nel.org>,
        lkml <linux-kernel@...r.kernel.org>
Subject: Re: [RFC] #MC mess

On Wed, Feb 19, 2020 at 09:21:15AM -0500, Steven Rostedt wrote:
> On Wed, 19 Feb 2020 09:15:41 +0100
> Peter Zijlstra <peterz@...radead.org> wrote:
> 
> > > 
> > > Tony, etc, can you ask your Intel contacts who care about this kind of
> > > thing to stop twiddling their thumbs and FIX IT?  The easy fix is
> > > utterly trivial.  Add a new instruction IRET_NON_NMI.  It does
> > > *exactly* the same thing as IRET except that it does not unmask NMIs.
> > > (It also doesn't unmask NMIs if it faults.)  No fancy design work.
> > > Future improvements can still happen on top of this.  
> > 
> > Yes please! Of course, we're stuck with the existing NMI entry crap
> > forever because legacy, but it would make all things NMI so much saner.
> 
> What would be nice is to have a NMI_IRET, that is defined as something
> that wont break legacy CPUs. Where it could be just a nop iret, or maybe
> if possible a "lock iret"? That is, not have a IRET_NON_NMI, as that
> would be all over the place, but just the iret for NMI itself. As
> that's in one place.

I don't think that matters much; alternatives should be able to deal
with all that either which way around.