linux-kernel - Re: [RFC PATCH 06/16] x86/split_lock: Save #AC setting for split lock in firmware in boot time and restore the setting in reboot

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Date:   Tue, 26 Jun 2018 12:02:21 +0100
From:   Alan Cox <gnomes@...rguk.ukuu.org.uk>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Alan Cox <alan@...ux.intel.com>, Fenghua Yu <fenghua.yu@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...e.hu>,
        "H. Peter Anvin" <hpa@...ux.intel.com>,
        Ashok Raj <ashok.raj@...el.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Rafael Wysocki <rafael.j.wysocki@...el.com>,
        Tony Luck <tony.luck@...el.com>,
        Ravi V Shankar <ravi.v.shankar@...el.com>,
        Arjan van de Ven <arjan@...radead.org>,
        linux-kernel <linux-kernel@...r.kernel.org>, x86 <x86@...nel.org>
Subject: Re: [RFC PATCH 06/16] x86/split_lock: Save #AC setting for split
 lock in firmware in boot time and restore the setting in reboot

On Tue, 26 Jun 2018 11:05:21 +0200
Peter Zijlstra <peterz@...radead.org> wrote:

> On Fri, Jun 22, 2018 at 04:11:07PM +0100, Alan Cox wrote:
> > On Thu, 2018-06-21 at 21:58 +0200, Peter Zijlstra wrote:  
> > > On Sun, May 27, 2018 at 08:45:55AM -0700, Fenghua Yu wrote:  
> > > > Firmware may contain split locked instructions.  
> > > 
> > > I think that's the wrong attitude. You should mandate in your BIOS
> > > development guide that Firmware _MUST_NOT_ contain unaligned LOCK
> > > prefixed instructions.
> > >   
> > 
> > In the longer term I would agree entirely with that sentiment.  
> 
> But then how do we deal with SMIs ?

On a system doing that level of real time you don't do SMIs.

I think Thomas comment that this shouldn't be in a production kernel
because the firmware people need to have their house in order before that
is a fair one.

(and I've already been poking people to make sure this is documented
properly as a requirement)

Alan