linux-kernel - Re: [PATCH 01/11] x86: Use asm goto to implement better modify_and

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Message-ID: <20130919083102.GB11427@tassilo.jf.intel.com>
Date:	Thu, 19 Sep 2013 01:31:02 -0700
From:	Andi Kleen <ak@...ux.intel.com>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>,
	Mike Galbraith <bitbucket@...ine.de>,
	Thomas Gleixner <tglx@...utronix.de>,
	Arjan van de Ven <arjan@...ux.intel.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>
Subject: Re: [PATCH 01/11] x86: Use asm goto to implement better
 modify_and_test() functions

On Wed, Sep 18, 2013 at 02:02:37PM -0500, H. Peter Anvin wrote:
> Yes, a bit sad.  We allow bracketing with the get/put_user_try/catch blocks, but that is x86-specific.
> 
> I don't think a generic option is possible without compiler support, but it might be possible to do better than we do know.

Letting the compiler do it is a bit risky, because it may open it up for
really large blocks, thus defeating the security advantages.

-Andi
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