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 8FFB5C0502E for ; Sun, 28 Aug 2022 01:57:43 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230137AbiH1B5l (ORCPT ); Sat, 27 Aug 2022 21:57:41 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:38230 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229458AbiH1B5j (ORCPT ); Sat, 27 Aug 2022 21:57:39 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C8BC73ED51 for ; Sat, 27 Aug 2022 18:57:37 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1661651856; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=3fZFEPgbjjmu6J/LmASfOOq+L6kipv2vP4maHTFsNbM=; b=ipILlsGuzhFm8jOPVEZQ9f2FBnAPZbbNpxucgl0ZXaF/ddIHdacibfBws5zqxLYh44Nqg+ XtRxQjecrjnO22qFbdnzzrPEhrZ+EeMFDTkb22hkYg1tN5LRGPKqf3Ncmv9cF/gNAdT1Yc rubUxL1l6WLBfybrcRaAGhDWd8+C+zo= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-376-z8xHsvapMrav6hnIavubbQ-1; Sat, 27 Aug 2022 21:57:33 -0400 X-MC-Unique: z8xHsvapMrav6hnIavubbQ-1 Received: from smtp.corp.redhat.com (int-mx09.intmail.prod.int.rdu2.redhat.com [10.11.54.9]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 5C727811E76; Sun, 28 Aug 2022 01:57:32 +0000 (UTC) Received: from localhost (ovpn-12-25.pek2.redhat.com [10.72.12.25]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 71506492C3B; Sun, 28 Aug 2022 01:57:31 +0000 (UTC) Date: Sun, 28 Aug 2022 09:57:28 +0800 From: Baoquan He To: linux-kernel@vger.kernel.org, Nicolas Saenz Julienne Cc: linux-arm-kernel@lists.infradead.org, catalin.marinas@arm.com, ardb@kernel.org, rppt@kernel.org, guanghuifeng@linux.alibaba.com, mark.rutland@arm.com, will@kernel.org, linux-mm@kvack.org, thunder.leizhen@huawei.com, wangkefeng.wang@huawei.com, kexec@lists.infradead.org Subject: Re: [PATCH 0/2] arm64, kdump: enforce to take 4G as the crashkernel low memory end Message-ID: References: <20220828005545.94389-1-bhe@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220828005545.94389-1-bhe@redhat.com> X-Scanned-By: MIMEDefang 2.85 on 10.11.54.9 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Forgot adding Nicolas when sending patch, add now. On 08/28/22 at 08:55am, Baoquan He wrote: > Problem: > ======= > On arm64, block and section mapping is supported to build page tables. > However, currently it enforces to take base page mapping for the whole > linear mapping if CONFIG_ZONE_DMA or CONFIG_ZONE_DMA32 is enabled and > crashkernel kernel parameter is set. This will cause longer time of the > linear mapping process during bootup and severe performance degradation > during running time. > > Root cause: > ========== > On arm64, crashkernel reservation relies on knowing the upper limit of > low memory zone because it needs to reserve memory in the zone so that > devices' DMA addressing in kdump kernel can be satisfied. However, the > limit on arm64 is variant. And the upper limit can only be decided late > till bootmem_init() is called. > > And we need to map the crashkernel region with base page granularity when > doing linear mapping, because kdump needs to protect the crashkernel region > via set_memory_valid(,0) after kdump kernel loading. However, arm64 doesn't > support well on splitting the built block or section mapping due to some > cpu reststriction [1]. And unfortunately, the linear mapping is done before > bootmem_init(). > > To resolve the above conflict on arm64, the compromise is enforcing to > take base page mapping for the entire linear mapping if crashkernel is > set, and CONFIG_ZONE_DMA or CONFIG_ZONE_DMA32 is enabed. Hence > performance is sacrificed. > > Solution: > ========= > To fix the problem, we should always take 4G as the crashkernel low > memory end in case CONFIG_ZONE_DMA or CONFIG_ZONE_DMA32 is enabled. > With this, we don't need to defer the crashkernel reservation till > bootmem_init() is called to set the arm64_dma_phys_limit. As long as > memblock init is done, we can conclude what is the upper limit of low > memory zone. > > 1) both CONFIG_ZONE_DMA or CONFIG_ZONE_DMA32 are disabled or memblock_start_of_DRAM() > 4G > limit = PHYS_ADDR_MAX+1 (Corner cases) > 2) CONFIG_ZONE_DMA or CONFIG_ZONE_DMA32 are enabled: > limit = 4G (generic case) > > Justification: > ============== > In fact, kdump kernel doesn't need to cover all peripherals' > addressing bits. Only device taken as dump target need be taken care of > and its addressing bits need be satified. Currently, there are two kinds > of dumping, dumped to local storage disk or dumped through network card to > remove storage server. It means only storage disk or netowrk card taken > as dump target need be consider if their addressing bits are satisfied. > For saving memory, we usually generate kdump specific initramfs including > necessary kernel modules for dump target devices. All other unnecessary > kernel modules are excluded and their correspondent devices won't be > initialized during kdump kernel bootup. > > So far, only Raspberry Pi 4 has some peripherals whcih can only address > 30 bits memory range as reported in [2]. Devices on all other arm64 systems > can address 32bits memory range. > > So by enforcing to take 4G as the crashkernel low memory end, the only > risk is if RPi4 owns storage disk or network card which can't address > 32bits memory range because they could be set as dump target. Even if > RPi4 truly has storage devices or network card which can only address 30 > bits memory range, it should be a corner case. We can document it since > crashkernel is more taken as a feature on server. Besides, RPi4 still can > use crashkernel=xM@yM to sepcify a location for 32bits addressing if it > really has that kind of storage device or network card and kdump is expected. > > [1] > https://lore.kernel.org/all/YrIIJkhKWSuAqkCx@arm.com/T/#u > > [2] > [PATCH v6 0/4] Raspberry Pi 4 DMA addressing support > https://lore.kernel.org/linux-arm-kernel/20190911182546.17094-1-nsaenzjulienne@suse.de/T/ > > > ====== > Question to Nicolas: > > Hi Nicolas, > > In cover letter of [2] patchset, you told RPi4 has peripherals which > can only address 30bits range. In below sentence, do you mean "the PCIe, > V3D, GENET" can't address 32bit range, or they have wider view of > address space the same as 40-bit DMA channels? I am confused about that. > > And the storage device or network card on RPi4 can address 32bit range > or 32bit range, do we have document or do you happen to know that? > > """ > The new Raspberry Pi 4 has up to 4GB of memory but most peripherals can > only address the first GB: their DMA address range is > 0xc0000000-0xfc000000 which is aliased to the first GB of physical > memory 0x00000000-0x3c000000. Note that only some peripherals have these > limitations: the PCIe, V3D, GENET, and 40-bit DMA channels have a wider > view of the address space by virtue of being hooked up trough a second > interconnect. > """ > > > Baoquan He (2): > arm64, kdump: enforce to take 4G as the crashkernel low memory end > arm64: remove unneed defer_reserve_crashkernel() and crash_mem_map > > arch/arm64/include/asm/memory.h | 5 ---- > arch/arm64/mm/init.c | 24 ++++++++------- > arch/arm64/mm/mmu.c | 53 ++++++++++++++------------------- > 3 files changed, 36 insertions(+), 46 deletions(-) > > > base-commit: 10d4879f9ef01cc6190fafe4257d06f375bab92c > -- > 2.34.1 >