From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail202.messagelabs.com (mail202.messagelabs.com [216.82.254.227]) by kanga.kvack.org (Postfix) with ESMTP id 1EABD6B004D for ; Wed, 27 Jan 2010 17:00:09 -0500 (EST) Date: Wed, 27 Jan 2010 22:59:59 +0100 From: Sebastian Andrzej Siewior Subject: Re: [PATCH] Flush dcache before writing into page to avoid alias Message-ID: <20100127215959.GC15325@Chamillionaire.breakpoint.cc> References: <979dd0561001202107v4ddc1eb7xa59a7c16c452f7a2@mail.gmail.com> <20100125133308.GA26799@desktop> <20100125115814.156d401d.akpm@linux-foundation.org> <20100125200004.GF22481@n2100.arm.linux.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: <20100125200004.GF22481@n2100.arm.linux.org.uk> Sender: owner-linux-mm@kvack.org To: Andrew Morton Cc: Russell King - ARM Linux , anfei , linux-mm@kvack.org, linux-kernel@vger.kernel.org, KOSAKI Motohiro , Jamie Lokier , linux-arm-kernel@lists.infradead.org List-ID: * Russell King - ARM Linux | 2010-01-25 20:00:04 [+0000]: >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 I just wanted to query what the status of this patch is. This patch seems to fix a real bug which causes a test suite to fail on ARM [0]. The test suite passes on my VIVT ARM with this patch. [0] http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=524003 Sebastian -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org