Re: [PATCH 8/8] x86, cleanups: Simplify sync_core() in the case of no CPUID

From: "H. Peter Anvin" <hpa@linux.intel.com>
To: Borislav Petkov <bp@alien8.de>, "H. Peter Anvin" <hpa@zytor.com>,
	Ingo Molnar <mingo@kernel.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Mario Gzuk <mariogzuk@technikz.de>
Subject: Re: [PATCH 8/8] x86, cleanups: Simplify sync_core() in the case of no CPUID
Date: Thu, 29 Nov 2012 13:24:26 -0800	[thread overview]
Message-ID: <50B7D28A.4000401@linux.intel.com> (raw)
In-Reply-To: <20121128204158.GC14635@liondog.tnic>

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