linux-kernel - Re: [PATCH v2 2/4] x86/split_lock: Align x86_capability to unsigned long to avoid split locked access

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Message-ID: <20180702141128.GA91188@romley-ivt3.sc.intel.com>
Date:   Mon, 2 Jul 2018 07:11:28 -0700
From:   Fenghua Yu <fenghua.yu@...el.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Fenghua Yu <fenghua.yu@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Dave Hansen <dave.hansen@...el.com>,
        Ingo Molnar <mingo@...hat.com>, H Peter Anvin <hpa@...or.com>,
        Ashok Raj <ashok.raj@...el.com>,
        Alan Cox <alan@...ux.intel.com>,
        Rafael Wysocki <rafael.j.wysocki@...el.com>,
        Tony Luck <tony.luck@...el.com>,
        Ravi V Shankar <ravi.v.shankar@...el.com>,
        linux-kernel <linux-kernel@...r.kernel.org>, x86 <x86@...nel.org>
Subject: Re: [PATCH v2 2/4] x86/split_lock: Align x86_capability to unsigned
 long to avoid split locked access

On Mon, Jul 02, 2018 at 02:18:59PM +0200, Peter Zijlstra wrote:
> On Fri, Jun 29, 2018 at 01:38:44PM -0700, Fenghua Yu wrote:
> > include/linux/efi.h because set_bit() sets bits in efi.flags:
> > -       unsigned long flags;
> > +       unsigned long flags __aligned(unsigned long);
> >  } efi;
> 
> Help me out here; how is the above change not a complete no-op?

You are right. Thomas pointed out 'flags' is already naturally aligned to
unsigned long because its type is unsigned long. So the __aligned()
is no-op.

Thanks.

-Fenghua