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 CCAF9C433FE for ; Thu, 16 Dec 2021 02:46:28 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233033AbhLPCq2 (ORCPT ); Wed, 15 Dec 2021 21:46:28 -0500 Received: from szxga02-in.huawei.com ([45.249.212.188]:16819 "EHLO szxga02-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230151AbhLPCq1 (ORCPT ); Wed, 15 Dec 2021 21:46:27 -0500 Received: from dggpemm500020.china.huawei.com (unknown [172.30.72.56]) by szxga02-in.huawei.com (SkyGuard) with ESMTP id 4JDxLX0hnKz91Px; Thu, 16 Dec 2021 10:45:40 +0800 (CST) Received: from dggpemm500006.china.huawei.com (7.185.36.236) by dggpemm500020.china.huawei.com (7.185.36.49) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2308.20; Thu, 16 Dec 2021 10:46:25 +0800 Received: from [10.174.178.55] (10.174.178.55) by dggpemm500006.china.huawei.com (7.185.36.236) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2308.20; Thu, 16 Dec 2021 10:46:24 +0800 Subject: Re: [PATCH v17 03/10] x86: kdump: use macro CRASH_ADDR_LOW_MAX in functions reserve_crashkernel() To: Baoquan He , Borislav Petkov CC: Thomas Gleixner , Ingo Molnar , , "H . Peter Anvin" , , Dave Young , Vivek Goyal , Eric Biederman , , Catalin Marinas , "Will Deacon" , , Rob Herring , Frank Rowand , , Jonathan Corbet , , Randy Dunlap , Feng Zhou , Kefeng Wang , "Chen Zhou" References: <20211210065533.2023-1-thunder.leizhen@huawei.com> <20211210065533.2023-4-thunder.leizhen@huawei.com> <20211216011040.GG3023@MiWiFi-R3L-srv> From: "Leizhen (ThunderTown)" Message-ID: <9513d74c-d4c7-babd-f823-8999e195d96d@huawei.com> Date: Thu, 16 Dec 2021 10:46:12 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:60.0) Gecko/20100101 Thunderbird/60.7.0 MIME-Version: 1.0 In-Reply-To: <20211216011040.GG3023@MiWiFi-R3L-srv> Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [10.174.178.55] X-ClientProxiedBy: dggems706-chm.china.huawei.com (10.3.19.183) To dggpemm500006.china.huawei.com (7.185.36.236) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2021/12/16 9:10, Baoquan He wrote: > On 12/15/21 at 02:28pm, Borislav Petkov wrote: >> On Fri, Dec 10, 2021 at 02:55:26PM +0800, Zhen Lei wrote: >>> @@ -518,7 +519,7 @@ static void __init reserve_crashkernel(void) >>> } >>> } >>> >>> - if (crash_base >= (1ULL << 32) && reserve_crashkernel_low()) { >>> + if (crash_base >= CRASH_ADDR_LOW_MAX && reserve_crashkernel_low()) { >>> memblock_phys_free(crash_base, crash_size); >>> return; >>> } >> >> That's not a equivalent transformation on X86_32. The original value (1ULL << 32) is inaccurate, and it enlarged the CRASH_ADDR_LOW upper limit. This is because when the memory is allocated from the low end, the address cannot exceed CRASH_ADDR_LOW_MAX, see "if (!high)" branch. If the memory is allocated from the high end, 'crash_base' is greater than or equal to (1ULL << 32), and naturally, it is greater than CRASH_ADDR_LOW_MAX. I think I should update the description, thanks. if (!high) crash_base = memblock_phys_alloc_range(crash_size, CRASH_ALIGN, CRASH_ALIGN, CRASH_ADDR_LOW_MAX); if (!crash_base) crash_base = memblock_phys_alloc_range(crash_size, CRASH_ALIGN, CRASH_ALIGN, CRASH_ADDR_HIGH_MAX); > > reserve_crashkernel_low() always return 0 on x86_32, so the not equivalent > transformation for x86_32 doesn't matter, I think. > > . >