Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751498Ab1B0DV2 (ORCPT ); Sat, 26 Feb 2011 22:21:28 -0500 Received: from mprc.pku.edu.cn ([162.105.203.9]:54018 "EHLO mprc.pku.edu.cn" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751351Ab1B0DVZ (ORCPT ); Sat, 26 Feb 2011 22:21:25 -0500 From: "Guan Xuetao" To: "'Arnd Bergmann'" Cc: , , "'Greg KH'" References: <014b01cbcdad$f110afb0$d3320f10$@mprc.pku.edu.cn> <201102171845.01177.arnd@arndb.de> In-Reply-To: <201102171845.01177.arnd@arndb.de> Subject: RE: [PATCH 05/12] unicore32 additional architecture files: low-level lib: uaccess Date: Sun, 27 Feb 2011 11:21:12 +0800 Message-ID: <017b01cbd62d$633fd070$29bf7150$@mprc.pku.edu.cn> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit X-Mailer: Microsoft Outlook 14.0 Thread-Index: AQJUJ5R0byzuScHkceok2M2VIwxC3QHwN80AkvSHNnA= Content-Language: zh-cn Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1486 Lines: 39 > -----Original Message----- > From: Arnd Bergmann [mailto:arnd@arndb.de] > Sent: Friday, February 18, 2011 1:45 AM > To: Guan Xuetao > Cc: linux-kernel@vger.kernel.org; linux-arch@vger.kernel.org; 'Greg KH' > Subject: Re: [PATCH 05/12] unicore32 additional architecture files: low-level lib: uaccess > > On Wednesday 16 February 2011, Guan Xuetao wrote: > > + > > +#define __kernel_ok (segment_eq(get_fs(), KERNEL_DS)) > > +#define __user_ok(addr, size) (((size) <= TASK_SIZE) \ > > + && ((addr) <= TASK_SIZE - (size))) > > +#define __access_ok(addr, size) (__kernel_ok || __user_ok((addr), (size))) > > A nice trick to simplify this is to introduce a per-process variable for comparing > the pointer, set_fs() then sets this variable to either TASK_SIZE or > UINT_MAX. Perhaps like this: 1. add a member named kaddr in thread_info 2. add following assignment codes in set_fs: current_thread_info()->kaddr = segment_eq(fs, KERNEL_DS) ? UINT_MAX : TASK_SIZE; 3. then __access_ok will be: #define addr #define __access_ok(addr, size) (((size) <= TASK_SIZE) \ && ((addr) <= current_thread_info()->kaddr) - (size))) > > This saves one conditional branch for each call to __access_ok. > > Arnd -- 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/