Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752436Ab0AYUAx (ORCPT ); Mon, 25 Jan 2010 15:00:53 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751550Ab0AYUAw (ORCPT ); Mon, 25 Jan 2010 15:00:52 -0500 Received: from caramon.arm.linux.org.uk ([78.32.30.218]:40795 "EHLO caramon.arm.linux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751120Ab0AYUAv (ORCPT ); Mon, 25 Jan 2010 15:00:51 -0500 Date: Mon, 25 Jan 2010 20:00:04 +0000 From: Russell King - ARM Linux To: Andrew Morton Cc: anfei , linux-mm@kvack.org, linux-kernel@vger.kernel.org, KOSAKI Motohiro , Jamie Lokier , linux-arm-kernel@lists.infradead.org Subject: Re: [PATCH] Flush dcache before writing into page to avoid alias Message-ID: <20100125200004.GF22481@n2100.arm.linux.org.uk> References: <979dd0561001202107v4ddc1eb7xa59a7c16c452f7a2@mail.gmail.com> <20100125133308.GA26799@desktop> <20100125115814.156d401d.akpm@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20100125115814.156d401d.akpm@linux-foundation.org> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1882 Lines: 44 On Mon, Jan 25, 2010 at 11:58:14AM -0800, Andrew Morton wrote: > On Mon, 25 Jan 2010 21:33:08 +0800 anfei wrote: > > > Hi Andrew, > > > > On Thu, Jan 21, 2010 at 01:07:57PM +0800, anfei zhou wrote: > > > The cache alias problem will happen if the changes of user shared mapping > > > is not flushed before copying, then user and kernel mapping may be mapped > > > into two different cache line, it is impossible to guarantee the coherence > > > after iov_iter_copy_from_user_atomic. So the right steps should be: > > > flush_dcache_page(page); > > > kmap_atomic(page); > > > write to page; > > > kunmap_atomic(page); > > > flush_dcache_page(page); > > > More precisely, we might create two new APIs flush_dcache_user_page and > > > flush_dcache_kern_page to replace the two flush_dcache_page accordingly. > > > > > > Here is a snippet tested on omap2430 with VIPT cache, and I think it is > > > not ARM-specific: > > > int val = 0x11111111; > > > fd = open("abc", O_RDWR); > > > addr = mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0); > > > *(addr+0) = 0x44444444; > > > tmp = *(addr+0); > > > *(addr+1) = 0x77777777; > > > write(fd, &val, sizeof(int)); > > > close(fd); > > > The results are not always 0x11111111 0x77777777 at the beginning as expected. > > > > > Is this a real bug or not necessary to support? > > Bug. If variable `addr' has type int* then the contents of that file > should be 0x11111111 0x77777777. You didn't tell us what the contents > were in the incorrect case, but I guess it doesn't matter. FYI, from a previous email from anfei: 0x44444444 0x77777777 -- 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/