Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757688Ab3CUHP5 (ORCPT ); Thu, 21 Mar 2013 03:15:57 -0400 Received: from mail-wg0-f44.google.com ([74.125.82.44]:44836 "EHLO mail-wg0-f44.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757071Ab3CUHP4 (ORCPT ); Thu, 21 Mar 2013 03:15:56 -0400 MIME-Version: 1.0 In-Reply-To: <20130321070357.GD28328@redhat.com> References: <20130321061838.GA28319@redhat.com> <20130321070357.GD28328@redhat.com> From: Roland Dreier Date: Thu, 21 Mar 2013 00:15:33 -0700 X-Google-Sender-Auth: hvQ-DchnR9TnfPQdbG5J8CJKWkY Message-ID: Subject: Re: [PATCH] rdma: don't make pages writeable if not requiested To: "Michael S. Tsirkin" Cc: "Michael R. Hines" , Sean Hefty , Hal Rosenstock , Yishai Hadas , Christoph Lameter , "linux-rdma@vger.kernel.org" , LKML , qemu-devel@nongnu.org Content-Type: text/plain; charset=ISO-8859-1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1168 Lines: 26 >> I think this change will break the case where userspace tries to >> register an MR with read-only permission, but intends locally through >> the CPU to write to the memory. > Shouldn't it set LOCAL_WRITE then? We're talking about the permissions for the register MR operation, right? (That's what the kernel RDMA driver code that does get_user_pages() sees) In that case, no, I don't see any reason for LOCAL_WRITE, since the only RDMA operations that will access this memory are remote reads. The writing (that triggers COW) is coming from normal process access triggering a page fault, etc. This is a pretty standard way of using RDMA... For example, I allocate some memory and register it for RDMA read (and pass the R_Key to the remote system) with only REMOTE_READ permission. Then I fill in the memory with the results of some computation and the remote system does an RDMA read to get those results. - R. -- 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/