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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
From:   Alan Cox <alan@linux.intel.com>
To:     Peter Zijlstra <peterz@infradead.org>,
        Fenghua Yu <fenghua.yu@intel.com>
Cc:     Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@elte.hu>,
        "H. Peter Anvin" <hpa@linux.intel.com>,
        Ashok Raj <ashok.raj@intel.com>,
        Dave Hansen <dave.hansen@intel.com>,
        Rafael Wysocki <rafael.j.wysocki@intel.com>,
        Tony Luck <tony.luck@intel.com>,
        Ravi V Shankar <ravi.v.shankar@intel.com>,
        Arjan van de Ven <arjan@infradead.org>,
        linux-kernel <linux-kernel@vger.kernel.org>, x86 <x86@kernel.org>
Date:   Fri, 22 Jun 2018 16:11:07 +0100
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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.

Alan