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Date:   Thu, 21 Nov 2019 21:25:08 +0100
From:   Peter Zijlstra <peterz@infradead.org>
To:     Fenghua Yu <fenghua.yu@intel.com>
Cc:     Andy Lutomirski <luto@kernel.org>,
        David Laight <David.Laight@aculab.com>,
        Ingo Molnar <mingo@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        H Peter Anvin <hpa@zytor.com>,
        Tony Luck <tony.luck@intel.com>,
        Ashok Raj <ashok.raj@intel.com>,
        Ravi V Shankar <ravi.v.shankar@intel.com>,
        linux-kernel <linux-kernel@vger.kernel.org>, x86 <x86@kernel.org>
Subject: Re: [PATCH v10 6/6] x86/split_lock: Enable split lock detection by
 kernel parameter
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On Thu, Nov 21, 2019 at 10:53:03AM -0800, Fenghua Yu wrote:

> 4. Otherwise, re-calculate addr to point the 32-bit address which contains
>    the bit and operate on the bit. No split lock.

That sounds confused, Even BT{,CRS} have a RmW size. There is no
'operate on the bit'.

Specifically I hard rely on BTSL to be a 32bit RmW, see commit:

  7aa54be29765 ("locking/qspinlock, x86: Provide liveness guarantee")

You might need to read this paper:

  https://www.cl.cam.ac.uk/~pes20/popl17/mixed-size.pdf