linux-kernel - Re: [PATCH] Use wbinvd() macro instead of raw inline assembly in .c files

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Date:	Fri, 20 Jul 2007 10:22:21 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Andi Kleen <ak@...e.de>
CC:	Glauber de Oliveira Costa <gcosta@...hat.com>,
	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	Muli Ben-Yehuda <muli@...ibm.com>
Subject: Re: [PATCH] Use wbinvd() macro instead of raw inline assembly in
 .c files

Andi Kleen wrote:
> On Friday 20 July 2007 00:55:40 Glauber de Oliveira Costa wrote:
>> This patch uses the already-existant wbinvd() macro to replace
>> raw assembly to perform this very same task in some .c files
>>     
>> Signed-off-by: Glauber de Oliveira Costa <gcosta@...hat.com>
>>
>> diff --git a/arch/x86_64/kernel/tce.c b/arch/x86_64/kernel/tce.c
>> index f61fb8e..afbb951 100644
>> --- a/arch/x86_64/kernel/tce.c
>> +++ b/arch/x86_64/kernel/tce.c
>> @@ -42,7 +42,7 @@ static inline void flush_tce(void* tceaddr)
>>  	if (cpu_has_clflush)
>>  		asm volatile("clflush (%0)" :: "r" (tceaddr));
>>  	else
>> -		asm volatile("wbinvd":::"memory");
>> +		wbinvd();
> 
> I guess it can be just removed there. I don' think there are any calgary 
> machines without clflush
> 

That seems like an unsafe thing to do (unless we err out somewhere);
lest there is, say, a microcode update disabling clflush due to an erratum.

It also seems to me we should have a macro for clflush(), especially
since it is "clflush (%0)" :: "r" in a number of places, which really
isn't correct; it should be "clflush %0" : "+m", both to allow
addressing modes to be used and to give gcc a modicum of a hint that
something is going on with a specific memory location.

	-hpa
-
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