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 16:39:43 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Fenghua Yu <fenghua.yu@...el.com>
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 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.

> 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... "

> 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>

-- 
Regards/Gruss,
    Boris.

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