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

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Message-ID: <50B7D28A.4000401@linux.intel.com>
Date:	Thu, 29 Nov 2012 13:24:26 -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 11/28/2012 12:41 PM, Borislav Petkov wrote:
> 
> While at it, you could correct this comment to adhere to kernel coding
> style:
> 
> 	/*
> 	 * cpuid is a barrier...
> 	 * ...
> 	 */
> 
>> +	asm volatile("cpuid" : "=a" (tmp) : "0" (1)
>> +		     : "ebx", "ecx", "edx", "memory");
> 
> ... and then write this in its shorter form:
> 
> 	tmp = cpuid_eax(1);
> 
> to have it a bit easier on the eyes.
> 

Thinking about it some more, there is another reason to not do this,
which is that we don't want this particular CPUID to be paravirtualized;
we're after the synchronizing side effect, not the CPUID return value
itself.

So let's leave it as a primitive; it gets too confusing otherwise.

	-hpa


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