From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-yk0-f178.google.com (mail-yk0-f178.google.com [209.85.160.178]) by kanga.kvack.org (Postfix) with ESMTP id 852616B0038 for ; Tue, 7 Jul 2015 19:12:06 -0400 (EDT) Received: by ykeo3 with SMTP id o3so71771356yke.0 for ; Tue, 07 Jul 2015 16:12:06 -0700 (PDT) Received: from g4t3426.houston.hp.com (g4t3426.houston.hp.com. [15.201.208.54]) by mx.google.com with ESMTPS id w5si124472ywf.213.2015.07.07.16.12.04 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 07 Jul 2015 16:12:05 -0700 (PDT) Message-ID: <1436310658.3214.85.camel@hp.com> Subject: Re: [PATCH v5 2/6] arch: unify ioremap prototypes and macro aliases From: Toshi Kani Date: Tue, 07 Jul 2015 17:10:58 -0600 In-Reply-To: <20150707160703.GR7021@wotan.suse.de> References: <20150622082427.35954.73529.stgit@dwillia2-desk3.jf.intel.com> <20150622161002.GB8240@lst.de> <20150701062352.GA3739@lst.de> <20150701065948.GA4355@lst.de> <20150701072828.GA4881@lst.de> <20150707095012.GQ7021@wotan.suse.de> <20150707101330.GJ7557@n2100.arm.linux.org.uk> <20150707160703.GR7021@wotan.suse.de> Content-Type: text/plain; charset="UTF-8" Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: "Luis R. Rodriguez" , Russell King - ARM Linux Cc: Christoph Hellwig , Andy Lutomirski , Benjamin Herrenschmidt , Geert Uytterhoeven , Julia Lawall , Dan Williams , Arnd Bergmann , Ingo Molnar , Borislav Petkov , "H. Peter Anvin" , Thomas Gleixner , Ross Zwisler , Andrew Morton , Juergen Gross , X86 ML , "linux-nvdimm@lists.01.org" , Konrad Rzeszutek Wilk , "linux-kernel@vger.kernel.org" , Stefan Bader , Linux MM , Ralf Baechle , Henrique de Moraes Holschuh , Michael Ellerman , Tejun Heo , Paul Mackerras , mcgrof@do-not-panic.com, "linux-arm-kernel@lists.infradead.org" On Tue, 2015-07-07 at 18:07 +0200, Luis R. Rodriguez wrote: > On Tue, Jul 07, 2015 at 11:13:30AM +0100, Russell King - ARM Linux > wrote: : > > On ARM, we (probably) have a lot of cases where ioremap() is used > > multiple > > times for the same physical address space, so we shouldn't rule out > > having > > multiple mappings of the same type. > > Why is that done? Don't worry if you are not sure why but only > speculate of the > practice's existence (sloppy drivers or lazy driver developers). FWIW > for x86 > IIRC I ended up concluding that overlapping ioremap() calls with the > same type > would work but not if they differ in type. Although I haven't > written a > grammer rule to hunt down overlapping ioremap() I suspected its use > was likely > odd and likely should be reconsidered. Would this be true for ARM too > ? Or are > you saying this should be a feature ? I don't expect an answer now > but I'm > saying we *should* all together decide on this, and if you're > inclined to > believe that this should ideally be avoided I'd like to hear that. If > you feel > strongly though this should be a feature I would like to know why. There are multiple mapping interfaces, and overlapping can happen among them as well. For instance, remap_pfn_range() (and io_remap_pfn_range(), which is the same as remap_pfn_range() on x86) creates a mapping to user space. The same physical ranges may be mapped to kernel and user spaces. /dev/mem is one example that may create a user space mapping to a physical address that is already mapped with ioremap() by other module. pmem and DAX also create mappings to the same NVDIMM ranges. DAX calls vm_insert_mixed(), which is particularly a problematic since vm_insert_mixed() does not verify aliasing. ioremap() and remap_pfn_range() call reserve_memtype() to verify aliasing on x86. reserve_memtype() is x86-specific and there is no arch-generic wrapper for such check. I think DAX could get a cache type from pmem to keep them in sync, though. Thanks, -Toshi -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org