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 bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 52EF0C433F5 for ; Thu, 16 Dec 2021 12:38:33 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:Date: Message-ID:From:References:CC:To:Subject:Reply-To:Content-ID: Content-Description:Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc :Resent-Message-ID:List-Owner; bh=iz305vPkkWyFIm694mLqnUUHg0gxwHqa21yTMbLwS9s=; b=bzClB5FchgGAvv4skeS+1JN8Ul xGWnV/W1M57CEIYgJcDSA20vN9zyfOqYlNZ7A4fSylLdCOJht2iZRV1Oi7f8k66j7s7nxLxAjPcUJ 1Oh+4B56F5k0KU4EIZgUO+Qj+udTLYsl3cTFs3AI20lLB9Yh6ymYfhP9GA9pYNH/2vps0OQG6VLso Hq249fKlP0U7jyW/JGCPh1ZBtlZIxaGCBXgtrIgG7FVuccpHHtPlPKVRidpgfX3oyaD7SjUhdBWc7 fs9Ewe1nwB+1aj+D9PcQOVtABtDxWC2wJPQo0wCdz3VWC+lv0mQOpnrSXz0cm5Ptzq40eV4OD6DkB sEUD0tsQ==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1mxpzs-005TDg-WD; Thu, 16 Dec 2021 12:36:34 +0000 Received: from szxga08-in.huawei.com ([45.249.212.255]) by bombadil.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1mxpZ1-005LhT-4f; Thu, 16 Dec 2021 12:08:49 +0000 Received: from dggpemm500024.china.huawei.com (unknown [172.30.72.56]) by szxga08-in.huawei.com (SkyGuard) with ESMTP id 4JF9mj4jm8z1DJs8; Thu, 16 Dec 2021 20:05:41 +0800 (CST) Received: from dggpemm500006.china.huawei.com (7.185.36.236) by dggpemm500024.china.huawei.com (7.185.36.203) 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 20:08:42 +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 20:08:41 +0800 Subject: Re: [PATCH v17 03/10] x86: kdump: use macro CRASH_ADDR_LOW_MAX in functions reserve_crashkernel() To: Borislav Petkov CC: Baoquan He , 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> <9513d74c-d4c7-babd-f823-8999e195d96d@huawei.com> From: "Leizhen (ThunderTown)" Message-ID: <35810a61-604e-9b90-2a7f-cfca6ae042ac@huawei.com> Date: Thu, 16 Dec 2021 20:08:30 +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: Content-Language: en-US X-Originating-IP: [10.174.178.55] X-ClientProxiedBy: dggems702-chm.china.huawei.com (10.3.19.179) To dggpemm500006.china.huawei.com (7.185.36.236) X-CFilter-Loop: Reflected X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20211216_040847_595151_3A53A0D9 X-CRM114-Status: GOOD ( 20.68 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 2021/12/16 19:07, Borislav Petkov wrote: > On Thu, Dec 16, 2021 at 10:46:12AM +0800, Leizhen (ThunderTown) wrote: >> The original value (1ULL << 32) is inaccurate > > I keep asking *why*? > >> and it enlarged the CRASH_ADDR_LOW upper limit. > > $ git grep -E "CRASH_ADDR_LOW\W" > $ > > I have no clue what you mean here. #ifdef CONFIG_X86_32 # define CRASH_ADDR_LOW_MAX SZ_512M # define CRASH_ADDR_HIGH_MAX SZ_512M #endif if (!high) (1) crash_base = memblock_phys_alloc_range(crash_size, CRASH_ALIGN, CRASH_ALIGN, CRASH_ADDR_LOW_MAX); if (!crash_base) (2) crash_base = memblock_phys_alloc_range(crash_size, CRASH_ALIGN, CRASH_ALIGN, CRASH_ADDR_HIGH_MAX); - if (crash_base >= (1ULL << 32) && reserve_crashkernel_low()) +(3) if (crash_base >= CRASH_ADDR_LOW_MAX && reserve_crashkernel_low()) If the memory of 'crash_base' is successfully allocated at (1), because the last parameter CRASH_ADDR_LOW_MAX is the upper bound, so we can sure that "crash_base < CRASH_ADDR_LOW_MAX". So that, reserve_crashkernel_low() will not be invoked at (3). That's why I said (1ULL << 32) is inaccurate and enlarge the CRASH_ADDR_LOW upper limit. If the memory of 'crash_base' is successfully allocated at (2), you see, CRASH_ADDR_HIGH_MAX = CRASH_ADDR_LOW_MAX = SZ_512M, the same as (1). In fact, "crashkernel=high," may not be recommended on X86_32. Is it possible that (CRASH_ADDR_HIGH_MAX >= 4G) and (CRASH_ADDR_LOW_MAX < 4G)? In this case, the memory allocated at (2) maybe over 4G. But why shouldn't CRASH_ADDR_LOW_MAX be equal to 4G at this point? > >> 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. > > I think you should explain why is (1ULL << 32) wrong. > > It came from: > > eb6db83d1059 ("x86/setup: Do not reserve crashkernel high memory if low reservation failed") > > which simply frees the high memory portion when the low reservation > fails. And the test for that is, is crash base > 4G. So that makes > perfect sense to me. > > So your change is a NOP on 64-bit and it is a NOP on 32-bit by virtue of > the _low() variant always returning 0 on 32-bit. > _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel