linux-kernel - Re: [PATCH v6 01/20] x86/common: Align cpu_caps_cleared and cpu_caps

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Date:   Thu, 4 Apr 2019 08:54:23 -0700
From:   Fenghua Yu <fenghua.yu@...el.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, H Peter Anvin <hpa@...or.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Ashok Raj <ashok.raj@...el.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Kalle Valo <kvalo@...eaurora.org>,
        Xiaoyao Li <xiaoyao.li@...el.com>,
        Michael Chan <michael.chan@...adcom.com>,
        Ravi V Shankar <ravi.v.shankar@...el.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        x86 <x86@...nel.org>, linux-wireless@...r.kernel.org,
        netdev@...r.kernel.org, kvm@...r.kernel.org
Subject: Re: [PATCH v6 01/20] x86/common: Align cpu_caps_cleared and
 cpu_caps_set to unsigned long

On Thu, Apr 04, 2019 at 04:39:43PM +0200, Borislav Petkov wrote:
> On Wed, Apr 03, 2019 at 02:21:47PM -0700, Fenghua Yu wrote:
> > cpu_caps_cleared and cpu_caps_set may not be aligned to unsigned long.
> > Atomic operations (i.e. set_bit and clear_bit) on the bitmaps may access
> 
> Please end function names with parentheses.

Sure.

> 
> > two cache lines (a.k.a. split lock) and lock the bus to block all memory
> 
> not "lock the bus" but "cause the CPU to do a bus lock... "

Sure.

> 
> > accesses from other processors to ensure atomicity.
> > 
> > To avoid the overall performance degradation from the bus locking, align
> > the two variables to unsigned long.
> > 
> > Defining the variables as unsigned long may also fix the issue because
> > they are naturally aligned to unsigned long. But that needs additional
> > code changes. Adding __aligned(unsigned long) is a simpler fix.
> > 
> > Signed-off-by: Fenghua Yu <fenghua.yu@...el.com>
> > ---
> >  arch/x86/kernel/cpu/common.c | 5 +++--
> >  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> With the above nitpicks addressed:
> 
> Reviewed-by: Borislav Petkov <bp@...e.de>

Thank you for your review!

-Fenghua