From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759804AbcIWNAd (ORCPT ); Fri, 23 Sep 2016 09:00:33 -0400 Received: from sender153-mail.zoho.com ([74.201.84.153]:25455 "EHLO sender153-mail.zoho.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1759127AbcIWNAa (ORCPT ); Fri, 23 Sep 2016 09:00:30 -0400 DomainKey-Signature: a=rsa-sha1; q=dns; c=nofws; s=zapps768; d=zoho.com; h=subject:to:references:cc:from:message-id:date:user-agent:mime-version:in-reply-to:content-type; b=hZJ/4mn90kzHumDaILMKV9gmAUG0ClMDjXlezpFtHDpi8VI7bxyZw6Yz0eCZC+fNfz9AOL8vomZp uMjIiyrLoTOTximUZnO/iOH76ZES5AF93MNwLuTbapjsakhF5yLm Subject: Re: [PATCH 1/1] lib/ioremap.c: avoid endless loop under ioremapping page unaligned ranges To: Michal Hocko 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> 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 From: zijun_hu Message-ID: <57E52762.9000702@zoho.com> Date: Fri, 23 Sep 2016 21:00:18 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.6.0 MIME-Version: 1.0 In-Reply-To: <20160923124244.GN4478@dhcp22.suse.cz> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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) 2, the rounding up start boundary maybe cause overflow, consider start boundary = 0xffffffff_fffff800