From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 9AAA6C433DB for ; Tue, 16 Feb 2021 03:13:11 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 6D96064DF0 for ; Tue, 16 Feb 2021 03:13:11 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229889AbhBPDMt (ORCPT ); Mon, 15 Feb 2021 22:12:49 -0500 Received: from foss.arm.com ([217.140.110.172]:53770 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229708AbhBPDMq (ORCPT ); Mon, 15 Feb 2021 22:12:46 -0500 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 0C92631B; Mon, 15 Feb 2021 19:12:01 -0800 (PST) Received: from [192.168.0.130] (unknown [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 9CFCF3F73D; Mon, 15 Feb 2021 19:11:57 -0800 (PST) Subject: Re: [PATCH v2 1/1] arm64: mm: correct the inside linear map boundaries during hotplug check To: Pavel Tatashin , Ard Biesheuvel Cc: Tyler Hicks , James Morris , Catalin Marinas , Will Deacon , Andrew Morton , Mike Rapoport , Logan Gunthorpe , Linux ARM , Linux Kernel Mailing List References: <20210215192237.362706-1-pasha.tatashin@soleen.com> <20210215192237.362706-2-pasha.tatashin@soleen.com> From: Anshuman Khandual Message-ID: <1790afff-eebd-1eda-a1b4-0062908f1f32@arm.com> Date: Tue, 16 Feb 2021 08:42:26 +0530 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2/16/21 1:21 AM, Pavel Tatashin wrote: > On Mon, Feb 15, 2021 at 2:34 PM Ard Biesheuvel wrote: >> >> On Mon, 15 Feb 2021 at 20:30, Pavel Tatashin wrote: >>> >>>> Can't we simply use signed arithmetic here? This expression works fine >>>> if the quantities are all interpreted as s64 instead of u64 >>> >>> I was thinking about that, but I do not like the idea of using sign >>> arithmetics for physical addresses. Also, I am worried that someone in >>> the future will unknowingly change it to unsigns or to phys_addr_t. It >>> is safer to have start explicitly set to 0 in case of wrap. >> >> memstart_addr is already a s64 for this exact reason. > > memstart_addr is basically an offset and it must be negative. For > example, this would not work if it was not signed: > #define vmemmap ((struct page *)VMEMMAP_START - (memstart_addr >> PAGE_SHIFT)) > > However, on powerpc it is phys_addr_t type. > >> >> Btw, the KASLR check is incorrect: memstart_addr could also be >> negative when running the 52-bit VA kernel on hardware that is only >> 48-bit VA capable. > > Good point! > > if (IS_ENABLED(CONFIG_ARM64_VA_BITS_52) && (vabits_actual != 52)) > memstart_addr -= _PAGE_OFFSET(48) - _PAGE_OFFSET(52); > > So, I will remove IS_ENABLED(CONFIG_RANDOMIZE_BASE) again. > > I am OK to change start_linear_pa, end_linear_pa to signed, but IMO > what I have now is actually safer to make sure that does not break > again in the future. An explicit check for the flip over and providing two different start addresses points would be required in order to use the new framework.