linux-kernel - Re: [PATCH] bitmap: separate bitmap parsing for user buffer and kernel buffer

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Message-ID: <p73odsqzgbz.fsf@verdi.suse.de>
Date:	05 Oct 2006 21:57:04 +0200
From:	Andi Kleen <ak@...e.de>
To:	Andrew Morton <akpm@...l.org>
Cc:	Joe Korty <joe.korty@...r.com>,
	Inaky Perez-Gonzalez <inaky@...ux.intel.com>,
	Paul Jackson <pj@....com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] bitmap: separate bitmap parsing for user buffer and kernel buffer

Andrew Morton <akpm@...l.org> writes:

> On Wed, 4 Oct 2006 17:56:30 -0700
> Reinette Chatre <reinette.chatre@...ux.intel.com> wrote:
> 
> > +			if (is_user) {
> > +				if (__get_user(c, buf++))
> > +					return -EFAULT;
> > +			}
> > +			else
> > +				c = *buf++;
> 
> Is this actually needed?  __get_user(kernel_address) works OK and (believe
> it or not, given all the stuff it involves) boils down to a single instruction.		

It is needed on lots of architectures that use separate address spaces
like sparc64, m68k, s390 (and on x86 with 4:4 patches) 

-Andi
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