From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Thu, 19 Oct 2006 00:17:47 -0700 From: Andrew Morton Subject: Re: [PATCH] mm:D-cache aliasing issue in cow_user_page Message-Id: <20061019001747.7da58920.akpm@osdl.org> In-Reply-To: <20061019.000027.41635681.davem@davemloft.net> References: <8764ejqp52.fsf@sw.ru> <20061018233302.a067d1e7.akpm@osdl.org> <20061019.000027.41635681.davem@davemloft.net> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: David Miller Cc: dmonakhov@openvz.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org List-ID: On Thu, 19 Oct 2006 00:00:27 -0700 (PDT) David Miller wrote: > > > 1452 if (__copy_from_user_inatomic(kaddr, uaddr, PAGE_SIZE)) > > > 1453 memset(kaddr, 0, PAGE_SIZE); > > > 1454 kunmap_atomic(kaddr, KM_USER0); > > > #### D-cache have to be flushed here. > > > #### It seems it is just forgotten. > > > > > > 1455 return; > > > 1456 > > > 1457 } > > > 1458 copy_user_highpage(dst, src, va); > > > #### Ok here. flush_dcache_page() called from this func if arch need it > > > 1459 } > > > > > > > This page has just been allocated and is private to the caller - there can > > be no userspace mappings of it. > > Unfortunately, the kernel has just touched the page and thus there are > active cache lines for the kernel side mapping. When we map this into > user space, userspace might see stale cachelines instead of the > memset() stores. hm. Has it always been that way or did something change? > Architectures typically take care of this in copy_user_page() and > clear_user_page(). The absolutely depend upon those two routines > being used for anonymous pages, and handle the D-cache issues there. Only anonymous pages? There are zillions of places where we modify pagecache without a flush, especially against the blockdev mapping (fs metadata). > But this code is going outside of that scope, and therefore needs > an explicit D-cache flush. OK, I'll add the patch. -- 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