linux-kernel - Re: [PATCH v10 6/6] x86/split_lock: Enable split lock detection by kernel parameter

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Message-ID: <20191121201951.GY4097@hirez.programming.kicks-ass.net>
Date:   Thu, 21 Nov 2019 21:19:51 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Fenghua Yu <fenghua.yu@...el.com>
Cc:     Andy Lutomirski <luto@...capital.net>,
        Andy Lutomirski <luto@...nel.org>,
        David Laight <David.Laight@...lab.com>,
        Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        H Peter Anvin <hpa@...or.com>,
        Tony Luck <tony.luck@...el.com>,
        Ashok Raj <ashok.raj@...el.com>,
        Ravi V Shankar <ravi.v.shankar@...el.com>,
        linux-kernel <linux-kernel@...r.kernel.org>, x86 <x86@...nel.org>
Subject: Re: [PATCH v10 6/6] x86/split_lock: Enable split lock detection by
 kernel parameter

On Thu, Nov 21, 2019 at 12:25:35PM -0800, Fenghua Yu wrote:

> > > We are working on a separate patch set to fix all split lock issues
> > > in atomic bitops. Per Peter Anvin and Tony Luck suggestions:
> > > 1. Still keep the byte optimization if nr is constant. No split lock.
> > > 2. If type of *addr is unsigned long, do quadword atomic instruction
> > >   on addr. No split lock.
> > > 3. If type of *addr is unsigned int, do word atomic instruction
> > >   on addr. No split lock.
> > > 4. Otherwise, re-calculate addr to point the 32-bit address which contains
> > >   the bit and operate on the bit. No split lock.

> Actually we only find 8 places calling atomic bitops using type casting
> "unsigned long *". After above changes, other 8 patches remove the type
> castings and then split lock free in atomic bitops in the current kernel.

Those above changes are never going to happen.