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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Message-ID: <20180621195823.GD13636@worktop.programming.kicks-ass.net>
Date:   Thu, 21 Jun 2018 21:58:23 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Fenghua Yu <fenghua.yu@...el.com>
Cc:     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>,
        Alan Cox <alan@...ux.intel.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 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.