From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755634AbbHFNIh (ORCPT ); Thu, 6 Aug 2015 09:08:37 -0400 Received: from mx2.suse.de ([195.135.220.15]:43344 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750758AbbHFNIf (ORCPT ); Thu, 6 Aug 2015 09:08:35 -0400 Subject: Re: [Patch V6 12/16] mm: provide early_memremap_ro to establish read-only mapping To: Juergen Gross , linux-kernel@vger.kernel.org, xen-devel@lists.xensource.com, konrad.wilk@oracle.com, david.vrabel@citrix.com, boris.ostrovsky@oracle.com References: <1437108697-4115-1-git-send-email-jgross@suse.com> <1437108697-4115-13-git-send-email-jgross@suse.com> <55C3573B.6020509@suse.cz> <55C35AD1.7010101@suse.com> Cc: Arnd Bergmann , linux-mm@kvack.org, linux-arch@vger.kernel.org From: Vlastimil Babka Message-ID: <55C35C51.1040005@suse.cz> Date: Thu, 6 Aug 2015 15:08:33 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.1.0 MIME-Version: 1.0 In-Reply-To: <55C35AD1.7010101@suse.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 08/06/2015 03:02 PM, Juergen Gross wrote: > On 08/06/2015 02:46 PM, Vlastimil Babka wrote: >> On 07/17/2015 06:51 AM, Juergen Gross wrote: >> >> ... and here for !CONFIG_MMU. >> >> So, what about CONFIG_MMU && !FIXMAP_PAGE_RO combinations? Which >> translates to CONFIG_MMU && !PAGE_KERNEL_RO. Maybe they don't exist, but >> then it's still awkward to see the combination in the code left >> unimplemented. > > At least there are some architectures without #define PAGE_KERNEL_RO but > testing CONFIG_MMU (arm, m68k, xtensa). > >> Would it be perhaps simpler to assume the same thing as in >> drivers/base/firmware_class.c ? >> >> /* Some architectures don't have PAGE_KERNEL_RO */ >> #ifndef PAGE_KERNEL_RO >> #define PAGE_KERNEL_RO PAGE_KERNEL >> #endif >> >> Or would it be dangerous here to silently lose the read-only protection? > > The only reason to use this function instead of early_memremap() is the > mandatory read-only mapping. My intention was to let the build fail in > case it is being used but not implemented. An architecture requiring the > function but having no PAGE_KERNEL_RO still can define FIXMAP_PAGE_RO. OK, in that case Acked-by: Vlastimil Babka > Juergen >