linux-kernel - Re: [PATCH] bitops: add

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Message-ID: <4FAACF1C.2060504@zytor.com>
Date:	Wed, 09 May 2012 13:10:04 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	"Michael S. Tsirkin" <mst@...hat.com>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Rob Landley <rob@...dley.net>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, x86@...nel.org,
	Arnd Bergmann <arnd@...db.de>,
	David Howells <dhowells@...hat.com>,
	Akinobu Mita <akinobu.mita@...il.com>,
	Alexey Dobriyan <adobriyan@...il.com>,
	Herbert Xu <herbert@...dor.hengli.com.au>,
	Stephen Rothwell <sfr@...b.auug.org.au>,
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-arch@...r.kernel.org, Gleb Natapov <gleb@...hat.com>,
	Paolo Bonzini <pbonzini@...hat.com>, kvm@...r.kernel.org,
	Avi Kivity <avi@...hat.com>,
	Marcelo Tosatti <mtosatti@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH] bitops: add _local bitops

On 05/09/2012 01:07 PM, Michael S. Tsirkin wrote:
> 
> In practice ATM any of the above will work. We probably don't even need
> to add barrier() calls since what we do afterwards is apic access which
> has an optimization barrier anyway.  But I'm fine with adding them in
> there just in case if that's what people want.
> 

If you have the optimization barrier anyway, then I'd be fine with you
just using __test_and_clear_bit() and add to a comment in
arch/x86/include/asm/bitops.h that KVM needs it to be locally atomic.

	-hpa
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