linux-kernel - Re: [PATCH 1 of 4] mm: add a ptep_modify

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Date:	Sat, 21 Jun 2008 08:06:36 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	xen-devel <xen-devel@...ts.xensource.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	kvm-devel <kvm-devel@...ts.sourceforge.net>,
	benh@...nel.crashing.org, x86@...nel.org,
	LKML <linux-kernel@...r.kernel.org>,
	Virtualization Mailing List <virtualization@...ts.osdl.org>,
	Hugh Dickins <hugh@...itas.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 1 of 4] mm: add a ptep_modify_prot transaction
	abstraction


* Jeremy Fitzhardinge <jeremy@...p.org> wrote:

> Jeremy Fitzhardinge wrote:
>> Linus Torvalds wrote:
>>   
>>> On Fri, 20 Jun 2008, Ingo Molnar wrote:
>>>       
>>>> okay - Jeremy, could you try the fix below? (or tip/master, i just  
>>>> pushed this out)
>>>>           
>>> Actually, don't try that one.
>>>
>>> It needs to be a _byte_ registers, so "ir" was wrong. You need "iq".
>>>       
>>
>> Doesn't work, unfortunately:
>> {standard input}:20511: Error: Incorrect register `%eax' used with `b'  
>> suffix
>>
>>         lock; orb %eax,1(%rdi)  # tmp64,
>>   
>
> This does work:
>
>                asm volatile(LOCK_PREFIX "orb %1,%0"
>                        : CONST_MASK_ADDR(nr, addr)
>                        : "iq" ((u8)CONST_MASK(nr))
>                        : "memory");
>
> (ie, explicitly casting the mask to u8)

ok, i've pushed out the fix with this.

	Ingo
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