Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751815Ab3CUSlx (ORCPT ); Thu, 21 Mar 2013 14:41:53 -0400 Received: from quartz.orcorp.ca ([184.70.90.242]:60334 "EHLO quartz.orcorp.ca" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751286Ab3CUSlv (ORCPT ); Thu, 21 Mar 2013 14:41:51 -0400 Date: Thu, 21 Mar 2013 12:41:35 -0600 From: Jason Gunthorpe To: "Michael S. Tsirkin" Cc: Roland Dreier , "Michael R. Hines" , Sean Hefty , Hal Rosenstock , Yishai Hadas , Christoph Lameter , "linux-rdma@vger.kernel.org" , LKML , qemu-devel@nongnu.org Subject: Re: [PATCH] rdma: don't make pages writeable if not requiested Message-ID: <20130321184135.GA8044@obsidianresearch.com> References: <20130321061838.GA28319@redhat.com> <20130321070357.GD28328@redhat.com> <20130321085107.GE28328@redhat.com> <20130321093946.GG28328@redhat.com> <20130321171115.GA653@obsidianresearch.com> <20130321181633.GC4366@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20130321181633.GC4366@redhat.com> User-Agent: Mutt/1.5.21 (2010-09-15) X-Broken-Reverse-DNS: no host name found for IP address 10.0.0.162 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1154 Lines: 24 On Thu, Mar 21, 2013 at 08:16:33PM +0200, Michael S. Tsirkin wrote: > This is the one I find redundant. Since the write will be done by > the adaptor under direct control by the application, why does it > make sense to declare this beforehand? If you don't want to allow > local write access to memory, just do not post any receive WRs with > this address. If you posted and regret it, reset the QP to cancel. This is to support your COW scenario - the app declares before hand to the kernel that it will write to the memory and the kernel ensures pages are dedicated to the app at registration time. Or the app says it will only read and the kernel could leave them shared. The adaptor enforces the access control to prevent a naughty app from writing to shared memory - think about mmap'ing libc.so and then using RDMA to write to the shared pages. It is necessary to ensure that is impossible. Jason -- 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/