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Date:   Sun, 24 Jun 2018 08:43:35 +0200 (CEST)
From:   Thomas Gleixner <tglx@linutronix.de>
To:     Fenghua Yu <fenghua.yu@intel.com>
cc:     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 02/16] x86/split_lock: Handle #AC exception for split
 lock in kernel mode
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On Sat, 23 Jun 2018, Fenghua Yu wrote:

> On Sun, Jun 24, 2018 at 02:55:08AM +0200, Thomas Gleixner wrote:
> > On Sat, 23 Jun 2018, Fenghua Yu wrote:
> > > On Sat, Jun 23, 2018 at 11:17:03AM +0200, Thomas Gleixner wrote:
> > > > On Fri, 22 Jun 2018, Fenghua Yu wrote:
> > It's not treated as failure. The firmware simply does not have an handler
> > for #AC installed and dies. I hope you yelled at the firmware people
> > already.
> 
> I think firmware does handle the split lock in its #AC handler because
> firmware shows the following log and system hangs:
> 
> !!!! IA32 Exception Type - 11(#AC - Alignment Check)  CPU Apic ID - 00000014!
> !
> ExceptionData - 00000000
> EIP  - 6A9DB6C3, CS  - 00000010, EFLAGS - 00010006
> ...

They even have a handler which makes the thing die, but never bothered to
enable #AC in the first place. So the handler is there to catch the case
that an operating system dares to enable #AC. Thank god, I don't have to
review that source code.

Thanks,

	tglx