Message-ID: <45246276.6000908@zytor.com>
Date: Wed, 04 Oct 2006 18:40:06 -0700
From: "H. Peter Anvin" <hpa@zytor.com>
User-Agent: Thunderbird 1.5.0.7 (X11/20060913)
MIME-Version: 1.0
To: Andrew Morton <akpm@osdl.org>
CC: Reinette Chatre <reinette.chatre@linux.intel.com>,
       Joe Korty <joe.korty@ccur.com>,
       Inaky Perez-Gonzalez <inaky@linux.intel.com>, Paul Jackson <pj@sgi.com>,
       linux-kernel@vger.kernel.org
Subject: Re: [PATCH] bitmap: separate bitmap parsing for user buffer and kernel
 buffer
References: <200610041756.30528.reinette.chatre@linux.intel.com> <20061004181003.6dae6065.akpm@osdl.org>
In-Reply-To: <20061004181003.6dae6065.akpm@osdl.org>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 968
Lines: 27

Andrew Morton wrote:
> On Wed, 4 Oct 2006 17:56:30 -0700
> Reinette Chatre <reinette.chatre@linux.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.		

On some architectures, kernel and user space are separate, overlapping 
address spaces.

If __bitmap_parse was an inline (and not exported), this would be okay; 
as it is, you end up doing the test dynamically under all circumstances, 
even though in most (if not all) cases the address space is know a priori.

	-hpa
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/