linux-kernel - Re: [PATCH 8/8] x86, cleanups: Simplify sync

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Message-ID: <50B7D180.9090605@linux.intel.com>
Date:	Thu, 29 Nov 2012 13:20:00 -0800
From:	"H. Peter Anvin" <hpa@...ux.intel.com>
To:	Borislav Petkov <bp@...en8.de>, "H. Peter Anvin" <hpa@...or.com>,
	Ingo Molnar <mingo@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Mario Gzuk <mariogzuk@...hnikz.de>
Subject: Re: [PATCH 8/8] x86, cleanups: Simplify sync_core() in the case of
 no CPUID

On 11/29/2012 01:18 PM, Borislav Petkov wrote:
> On Thu, Nov 29, 2012 at 01:06:20PM -0800, H. Peter Anvin wrote:
>> It doesn't matter in that context, as the surrounding MSR references
>> have barriers, but what I'm refering to is the "memory" barrier.
> 
> Ok, but the only difference between the two versions is this line:
> 
>         movl    %esi, %ecx      # tmp144, ecx
> 
> coming from the cpuid_eax() function. So the memory barrier is the same
> and in the right place in both cases.
> 

In the case of that one call site, yes, because the MSR references
include the barrier.  Other sites, current or future, may not have the
same property.

	-hpa


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