linux-kernel - Re: [RFC PATCH 02/16] x86/split_lock: Handle #AC exception for split lock in kernel mode

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Date:   Sat, 23 Jun 2018 18:17:38 -0700
From:   Fenghua Yu <fenghua.yu@...el.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Fenghua Yu <fenghua.yu@...el.com>, 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 02/16] x86/split_lock: Handle #AC exception for split
 lock in kernel mode

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
...

> If that is a real wide spread issue in practice, then we might have to go
> for some ugly workarounds, but we won't find out when we add them
> upfront. So testing will show what's wrong in firmware land and we can
> handle it from there. It's a completely orthogonal issue and has nothing to
> do with the core functionality.

Sure

Thanks.

-Fenghua