Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752318Ab3CUTPZ (ORCPT ); Thu, 21 Mar 2013 15:15:25 -0400 Received: from mx1.redhat.com ([209.132.183.28]:56363 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751100Ab3CUTPX (ORCPT ); Thu, 21 Mar 2013 15:15:23 -0400 Date: Thu, 21 Mar 2013 21:15:41 +0200 From: "Michael S. Tsirkin" To: Jason Gunthorpe 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: <20130321191541.GB5272@redhat.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> <20130321184135.GA8044@obsidianresearch.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20130321184135.GA8044@obsidianresearch.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1665 Lines: 37 On Thu, Mar 21, 2013 at 12:41:35PM -0600, Jason Gunthorpe wrote: > 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. Someone here is confused. LOCAL_WRITE/absence of it does not address COW, it breaks COW anyway. Are you now saying we should change rdma so without LOCAL_WRITE it will not break COW? > 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 That's why it's redundant: we can't trust an application to tell us 'this page is writeable', we must get this info from kernel. And so there's apparently no need for application to tell adaptor about LOCAL_WRITE. -- MST -- 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/