From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1030412AbcIWNdk (ORCPT ); Fri, 23 Sep 2016 09:33:40 -0400 Received: from mail-wm0-f68.google.com ([74.125.82.68]:35207 "EHLO mail-wm0-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754692AbcIWNde (ORCPT ); Fri, 23 Sep 2016 09:33:34 -0400 Date: Fri, 23 Sep 2016 15:33:31 +0200 From: Michal Hocko To: zijun_hu Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, zijun_hu@htc.com, Andrew Morton , tj@kernel.org, mingo@kernel.org, rientjes@google.com, iamjoonsoo.kim@lge.com, mgorman@techsingularity.net Subject: Re: [PATCH 1/1] lib/ioremap.c: avoid endless loop under ioremapping page unaligned ranges Message-ID: <20160923133330.GO4478@dhcp22.suse.cz> References: <57E20A69.5010206@zoho.com> <20160922124735.GB11204@dhcp22.suse.cz> <35661a34-c3e0-0ec2-b58f-ee59bef4e4d4@zoho.com> <20160923084551.GG4478@dhcp22.suse.cz> <20160923124244.GN4478@dhcp22.suse.cz> <57E52762.9000702@zoho.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <57E52762.9000702@zoho.com> User-Agent: Mutt/1.6.0 (2016-04-01) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri 23-09-16 21:00:18, zijun_hu wrote: > On 09/23/2016 08:42 PM, Michal Hocko wrote: > >>>> no, it don't work for many special case > >>>> for example, provided PMD_SIZE=2M > >>>> mapping [0x1f8800, 0x208800) virtual range will be split to two ranges > >>>> [0x1f8800, 0x200000) and [0x200000,0x208800) and map them separately > >>>> the first range will cause dead loop > >>> > >>> I am not sure I see your point. How can we deadlock if _both_ addresses > >>> get aligned to the page boundary and how does PMD_SIZE make any > >>> difference. > >>> > >> i will take a example to illustrate my considerations > >> provided PUD_SIZE == 1G, PMD_SIZE == 2M, PAGE_SIZE == 4K > >> it is used by arm64 normally > >> > >> we want to map virtual range [0xffffffff_ffc08800, 0xffffffff_fffff800) by > >> ioremap_page_range(),ioremap_pmd_range() is called to map the range > >> finally, ioremap_pmd_range() will call > >> ioremap_pte_range(pmd, 0xffffffff_ffc08800, 0xffffffff_fffe0000) and > >> ioremap_pte_range(pmd, 0xffffffff_fffe0000, 0xffffffff fffff800) separately > > > > but those ranges are not aligned and it ioremap_page_range fix them up > > to _be_ aligned then there is no problem, right? So either I am missing > > something or we are talking past each other. > > > my complementary considerations are show below > > why not to round up the range start boundary to page aligned? > 1, it don't remain consistent with the original logic > take map [0x1800, 0x4800) as example > the original logic map range [0x1000, 0x2000), but rounding up start boundary > don't mapping the range [0x1000, 0x2000) just look at how we do that for the mmap... > 2, the rounding up start boundary maybe cause overflow, consider start boundary = > 0xffffffff_fffff800 this is just insane -- Michal Hocko SUSE Labs