From mboxrd@z Thu Jan 1 00:00:00 1970 From: Stefan Richter Subject: Re: PAGE_KERNEL_RO Date: Thu, 13 Jan 2011 07:34:58 +0100 Message-ID: <20110113073458.2179590a@stein> References: <20110112160722.6486a6c2.akpm@linux-foundation.org> <1294877484.9586.66.camel@pasglop> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Return-path: Received: from einhorn.in-berlin.de ([192.109.42.8]:37135 "EHLO einhorn.in-berlin.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751521Ab1AMGfW (ORCPT ); Thu, 13 Jan 2011 01:35:22 -0500 In-Reply-To: <1294877484.9586.66.camel@pasglop> Sender: linux-arch-owner@vger.kernel.org List-ID: To: Benjamin Herrenschmidt Cc: Andrew Morton , linux-arch@vger.kernel.org, linux1394-devel@lists.sourceforge.net, Clemens Ladisch On Jan 13 Benjamin Herrenschmidt wrote at linux-arch: > On Wed, 2011-01-12 at 16:07 -0800, Andrew Morton wrote: > > drivers/firewire/ohci.c now needs PAGE_KERNEL_RO, but many > > architectures don't implement it. Broke my sparc64 build. > > Some architectures actually cannot implement it even... at least some > variants of powerpc MMUs don't have a combination of protection bits > that allow a kernel-only RO mapping (yeah odd). The simplest perceivable fix, to disable firewire-ohci on architectures which don't have PAGE_KERNEL_RO, would be bad since there are actually sparc64 machines with these controllers. As far as I can tell, the new RO mapping in firewire-ohci can as well be an r/w mapping. We just never need to write at these virtual addresses. So, should we just change the driver to map it r/w when we can't have PAGE_KERNEL_RO, or for simplicity on all architectures? -- Stefan Richter -=====-==-== ---= -==-= http://arcgraph.de/sr/