From mboxrd@z Thu Jan 1 00:00:00 1970 From: James Bottomley Subject: Re: [patch 05/16] mm: flush dcache before writing into page to avoid alias Date: Wed, 03 Feb 2010 12:25:07 -0600 Message-ID: <1265221507.2873.369.camel@mulgrave.site> References: <201002022144.o12Li2wj015711@imap1.linux-foundation.org> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Return-path: Received: from bedivere.hansenpartnership.com ([66.63.167.143]:55319 "EHLO bedivere.hansenpartnership.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754272Ab0BCSZO (ORCPT ); Wed, 3 Feb 2010 13:25:14 -0500 In-Reply-To: <201002022144.o12Li2wj015711@imap1.linux-foundation.org> Sender: linux-arch-owner@vger.kernel.org List-ID: To: akpm@linux-foundation.org Cc: torvalds@linux-foundation.org, anfei.zhou@gmail.com, linux-arch@vger.kernel.org, miklos@szeredi.hu, nickpiggin@yahoo.com.au, rmk@arm.linux.org.uk, stable@kernel.org On Tue, 2010-02-02 at 13:44 -0800, akpm@linux-foundation.org wrote: > From: anfei zhou > > 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); This is likely unnecessary if the page has come down a standard path ... for fuse, it is possible it didn't go through __get_user_pages(). > 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. We already have one of those: flush_kernel_dcache_page(). James