Re: [PATCH] bitmap: separate bitmap parsing for user buffer andkernel buffer

[Andrew Morton]

On 05 Oct 2006 21:57:04 +0200
Andi Kleen <ak@xxxxxxx> wrote:

> Andrew Morton <akpm@xxxxxxxx> writes:
> 
> > On Wed, 4 Oct 2006 17:56:30 -0700
> > Reinette Chatre <reinette.chatre@xxxxxxxxxxxxxxx> 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) 
> 

It needs set_fs(KERNEL_DS) if we're going to use __get_user() on both
callpaths.

I think we'll stick with the `is_user' version - less tricky, clearer.
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