linux-kernel - Re: [PATCH v16] x86/split_lock: Enable split lock detection by kernel

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Message-Id: <4E95BFAA-A115-4159-AA4F-6AAB548C6E6C@gmail.com>
Date:   Sat, 25 Jan 2020 14:43:33 -0800
From:   Mark D Rustad <mrustad@...il.com>
To:     "Luck, Tony" <tony.luck@...el.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Arvind Sankar <nivedita@...m.mit.edu>,
        "Christopherson, Sean J" <sean.j.christopherson@...el.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        "Yu, Fenghua" <fenghua.yu@...el.com>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        H Peter Anvin <hpa@...or.com>,
        "Raj, Ashok" <ashok.raj@...el.com>,
        "Shankar, Ravi V" <ravi.v.shankar@...el.com>,
        linux-kernel <linux-kernel@...r.kernel.org>, x86 <x86@...nel.org>
Subject: Re: [PATCH v16] x86/split_lock: Enable split lock detection by kernel

On Jan 25, 2020, at 2:07 PM, Luck, Tony <tony.luck@...el.com> wrote:

>   - Transitioning between modes at runtime isn't supported and disabling
>     is tracked per task, so hardware will always reach a steady state that
>     matches the configured mode.

Maybe "isn't supported" is not really the right wording. I would think that  
if it truly weren't supported that you really shouldn't be changing the  
mode at all at runtime. Do you really just mean "isn't atomic"? Or is there  
something deeper about it? If so, are there other possible risks associated  
with changing the mode at runtime?

Sorry, the wording just happened to catch my eye and my mind immediately  
went to "how can you be doing something that is not supported?"

--
Mark Rustad, MRustad@...il.com

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