linux-kernel - Re: [PATCH v15] x86/split_lock: Enable split lock detection by kernel

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Message-ID: <20200125235130.GA565241@rani.riverdale.lan>
Date:   Sat, 25 Jan 2020 18:51:31 -0500
From:   Arvind Sankar <nivedita@...m.mit.edu>
To:     "Luck, Tony" <tony.luck@...el.com>
Cc:     Arvind Sankar <nivedita@...m.mit.edu>,
        Thomas Gleixner <tglx@...utronix.de>,
        "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 v15] x86/split_lock: Enable split lock detection by kernel

On Sat, Jan 25, 2020 at 01:50:03PM -0800, Luck, Tony wrote:
> > 
> > I might be missing something but shouldnt this be !nextflag given the
> > flag being unset is when the task wants sld?
> 
> That logic is convoluted ... but Thomas showed me a much better
> way that is also much simpler ... so this code has gone now. The
> new version is far easier to read (argument is flags for the new task
> that we are switching to)
> 
> void switch_to_sld(unsigned long tifn)
> {
>         __sld_msr_set(tifn & _TIF_SLD);
> }
> 
> -Tony

why doesnt this have the same problem though? tifn & _TIF_SLD still
needs to be logically negated no?