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Date:   Fri, 22 Jun 2018 11:18:18 +0200 (CEST)
From:   Thomas Gleixner <tglx@linutronix.de>
To:     Fenghua Yu <fenghua.yu@intel.com>
cc:     Peter Zijlstra <peterz@infradead.org>, 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>,
        Alan Cox <alan@linux.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>
Subject: Re: [RFC PATCH 00/16] x86/split_lock: Enable #AC exception for split
 locked accesses
In-Reply-To: <20180621220003.GD114883@romley-ivt3.sc.intel.com>
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References: <1527435965-202085-1-git-send-email-fenghua.yu@intel.com> <20180621193738.GA13636@worktop.programming.kicks-ass.net> <20180621201851.GC114883@romley-ivt3.sc.intel.com> <alpine.DEB.2.21.1806212223480.1591@nanos.tec.linutronix.de>
 <20180621220003.GD114883@romley-ivt3.sc.intel.com>
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On Thu, 21 Jun 2018, Fenghua Yu wrote:
> Right. Code won't cover the early boot process. It only covers boot process
> after the feature is enabled.

That's broken. #AC wants to be enabled early as any other exception. The
reason why you cannot enable it is because your exception handler is a
total trainwreck, but it's even a trainwreck later on.

> After disabling #AC split lock after catching #AC once, any future split
> lock will not generate #AC any more.

That's perfectly fine for the kernel. Issue a prominent warning and stuff
gets fixed.

Thanks,

	tglx