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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 10508C433EF for ; Wed, 19 Jan 2022 01:16:08 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1350588AbiASBQH (ORCPT ); Tue, 18 Jan 2022 20:16:07 -0500 Received: from szxga08-in.huawei.com ([45.249.212.255]:31102 "EHLO szxga08-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S238605AbiASBQG (ORCPT ); Tue, 18 Jan 2022 20:16:06 -0500 Received: from dggpemm500021.china.huawei.com (unknown [172.30.72.57]) by szxga08-in.huawei.com (SkyGuard) with ESMTP id 4Jdng41pwRz1FCfC; Wed, 19 Jan 2022 09:12:16 +0800 (CST) Received: from dggpemm500001.china.huawei.com (7.185.36.107) by dggpemm500021.china.huawei.com (7.185.36.109) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2308.21; Wed, 19 Jan 2022 09:16:01 +0800 Received: from [10.174.177.243] (10.174.177.243) by dggpemm500001.china.huawei.com (7.185.36.107) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256) id 15.1.2308.21; Wed, 19 Jan 2022 09:15:56 +0800 Message-ID: <8a24ef1d-1c93-416d-cfbe-e63aacfb25cc@huawei.com> Date: Wed, 19 Jan 2022 09:15:55 +0800 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:91.0) Gecko/20100101 Thunderbird/91.2.0 Subject: Re: [PATCH v2 1/2] powerpc: Fix virt_addr_valid() check Content-Language: en-US To: Christophe Leroy , Nicholas Piggin , Andrew Morton , "Benjamin Herrenschmidt" , Kees Cook , Laura Abbott , "linux-kernel@vger.kernel.org" , "linux-mm@kvack.org" , "linuxppc-dev@lists.ozlabs.org" , Mark Rutland , Michael Ellerman , Paul Mackerras References: <20211225120621.13908-1-wangkefeng.wang@huawei.com> <20211225120621.13908-2-wangkefeng.wang@huawei.com> <09ed46a5-6df3-ffc0-8243-61612c06153a@huawei.com> <1641871726.fshx7g5r92.astroid@bobo.none> From: Kefeng Wang In-Reply-To: Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 8bit X-Originating-IP: [10.174.177.243] X-ClientProxiedBy: dggeme707-chm.china.huawei.com (10.1.199.103) To dggpemm500001.china.huawei.com (7.185.36.107) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2022/1/11 14:04, Christophe Leroy wrote: > > Le 11/01/2022 à 05:37, Nicholas Piggin a écrit : >> Excerpts from Kefeng Wang's message of January 8, 2022 9:58 pm: >>> Hi PPC maintainers， ping.. >> Hmm. I might have confused myself about this. I'm going back and >> trying to work out what I was thinking when I suggested it. This >> works on 64e because vmalloc space is below the kernel linear map, >> right? >> >> On 64s it is the other way around and it is still possible to enable >> flatmem on 64s. Altough we might just not hit the problem there because >> __pa() will not mask away the vmalloc offset for 64s so it will still >> return something that's outside the pfn_valid range for flatmem. That's >> very subtle though. > That's the way it works on PPC32 at least, so for me it's not chocking > to have it work the same way on PPC64s. > > The main issue here is the way __pa() works. On PPC32 __pa = va - > PAGE_OFFSET, so it works correctly for any address. > On PPC64, __pa() works by masking out the 2 top bits instead of > substracting PAGE_OFFSET, so the test must add a verification that we > really have the 2 top bits set at first. This is what (addr >= > PAGE_OFFSET) does. Once this first test is done, we can perfectly rely > on pfn_valid() just like PPC32, I see absolutely no point in an > additionnal test checking the addr is below KERN_VIRT_START. Hi Christophe and Nicholas， for ppc32， I think we need check the upper limit, eg,  addr >= PAGE_OFFSET && addr < high_memory arch/powerpc/mm/mem.c:  high_memory = (void *) __va(max_low_pfn * PAGE_SIZE); for ppc32 max_low_pfn is the upper low memory pfn,  and For ppc64, high_memory is the max memory pfn, it looks good too, correct me if I'm wrong, if the above check is ok, I will send a new v3,  thanks. > > >> The checks added to __pa actually don't prevent vmalloc memory from >> being passed to it either on 64s, only a more basic test. > That's correct. It is the role of pfn_valid() to check that. > > Christophe > >> I think 64s wants (addr >= PAGE_OFFSET && addr < KERN_VIRT_START) as >> the condition. Could possibly add that check to __pa as well to >> catch vmalloc addresses. >> >> Thanks, >> Nick >> >>