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 0A26DC43334 for ; Tue, 21 Jun 2022 09:29:00 +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:References: Message-ID:Subject:Cc:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=WD9u3RRBGje6X0NTociWJ5hK43vRmGx/Wk4FX91BAfM=; b=uy5iSUiBJPY7lf gx6vDZrBMzHFsAxS8CTjwPleoWP1PntAE6wsm4rNdQFX/usBHkS2W+vQj+ahTU4HFpEczW5kHXGWi sIG6IaTz2PygFCv8cA2/W7Tj7f5+tgsI6XYtyp8Is5UFyee/K9hKbfHILE07FFCbJuvKbVA9FK0/G 9KshScGpVoU6rOPbxVwYw/zKJ29kyYJIAKXQcE7CUql9xDr9COVDoUxG/WbmLxwaCnqp8StDfSGDV +fFx9d2YCpx6Cyu6REqyiYUFeod5qwSoyo9Ww9hyIQXiSOvab5cIC58ySlnuk01kliUochgJr4LQr Wptad30odW5ts7GWDcsw==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1o3aAu-004cvl-Ce; Tue, 21 Jun 2022 09:27:56 +0000 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]) by bombadil.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1o3aAr-004cu3-4C for linux-arm-kernel@lists.infradead.org; Tue, 21 Jun 2022 09:27:54 +0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1655803670; 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: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=1/6eJspt/AVzBoz5mItJSgxql1F5f7nb/z62lzZC//s=; b=h92MBdQ60YyfZtTbeTYIsHZWShRLkjKqTjvj2+fhkEzm8r35rgkMIsdzQo3u8IA9caCYqf 5pxhNmMkM6OnewRaPK1fLodCkqUaE5yz1EyXfayLo9+RONtmB/JSoZisruRS5D5+BQzVE2 ixudyhNSW9jUk8rYMuFumpZtVxYWyig= 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-2-MQve9TMLMYyX3G1gVtvhfA-1; Tue, 21 Jun 2022 05:27:47 -0400 X-MC-Unique: MQve9TMLMYyX3G1gVtvhfA-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.rdu2.redhat.com [10.11.54.1]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 539A280B70F; Tue, 21 Jun 2022 09:27:46 +0000 (UTC) Received: from localhost (ovpn-12-183.pek2.redhat.com [10.72.12.183]) by smtp.corp.redhat.com (Postfix) with ESMTPS id A52A540CFD0A; Tue, 21 Jun 2022 09:27:44 +0000 (UTC) Date: Tue, 21 Jun 2022 17:27:40 +0800 From: Baoquan He To: Kefeng Wang Cc: Zhen Lei , Catalin Marinas , Ard Biesheuvel , Mark Rutland , Thomas Gleixner , Ingo Molnar , Borislav Petkov , x86@kernel.org, "H . Peter Anvin" , Eric Biederman , Rob Herring , Frank Rowand , devicetree@vger.kernel.org, Dave Young , Vivek Goyal , kexec@lists.infradead.org, linux-kernel@vger.kernel.org, Will Deacon , linux-arm-kernel@lists.infradead.org, Jonathan Corbet , linux-doc@vger.kernel.org, Randy Dunlap , Feng Zhou , Chen Zhou , John Donnelly , Dave Kleikamp , liushixin Subject: Re: [PATCH 5/5] arm64: kdump: Don't defer the reservation of crash high memory Message-ID: References: <20220613080932.663-1-thunder.leizhen@huawei.com> <20220613080932.663-6-thunder.leizhen@huawei.com> <3f66323d-f371-b931-65fb-edfae0f01c88@huawei.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <3f66323d-f371-b931-65fb-edfae0f01c88@huawei.com> X-Scanned-By: MIMEDefang 2.84 on 10.11.54.1 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20220621_022753_299227_C1061008 X-CRM114-Status: GOOD ( 41.26 ) 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="iso-8859-1" Content-Transfer-Encoding: quoted-printable Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 06/21/22 at 02:24pm, Kefeng Wang wrote: > = > On 2022/6/21 13:33, Baoquan He wrote: > > Hi, > > = > > On 06/13/22 at 04:09pm, Zhen Lei wrote: > > > If the crashkernel has both high memory above DMA zones and low memory > > > in DMA zones, kexec always loads the content such as Image and dtb to= the > > > high memory instead of the low memory. This means that only high memo= ry > > > requires write protection based on page-level mapping. The allocation= of > > > high memory does not depend on the DMA boundary. So we can reserve the > > > high memory first even if the crashkernel reservation is deferred. > > > = > > > This means that the block mapping can still be performed on other ker= nel > > > linear address spaces, the TLB miss rate can be reduced and the system > > > performance will be improved. > > Ugh, this looks a little ugly, honestly. > > = > > If that's for sure arm64 can't split large page mapping of linear > > region, this patch is one way to optimize linear mapping. Given kdump > > setting is necessary on arm64 server, the booting speed is truly > > impacted heavily. > = > Is there some conclusion or discussion that arm64 can't split large page > mapping? Yes, please see below commit log. = commit d27cfa1fc823 ("arm64: mm: set the contiguous bit for kernel mappings= where appropriate") > = > Could the crashkernel reservation (and Kfence pool) be splited dynamicall= y? For crashkernel region, we have arch_kexec_protect_crashkres() to secure the region, and crash_shrink_memory() could be called to shrink it. While crahshkernel region could be crossig part of a block mapping or secti= on mapping and the mapping need be splitted, that will cause TLB conflicts. > = > I found Mark replay "arm64: remove page granularity limitation from > KFENCE"[1], > = > =A0 "We also avoid live changes from block<->table mappings, since the > =A0 archtitecture gives us very weak guarantees there and generally requi= res > =A0 a Break-Before-Make sequence (though IIRC this was tightened up > =A0 somewhat, so maybe going one way is supposed to work). Unless it's > =A0 really necessary, I'd rather not split these block mappings while > =A0 they're live." > = > Hi Mark and Catalin,=A0 could you give some comment,=A0 many thanks. > = > [1] https://lore.kernel.org/lkml/20210920101938.GA13863@C02TD0UTHF1T.loca= l/T/#m1a7f974593f5545cbcfc0d21560df4e7926b1381 > = > = > > = > > However, I would suggest letting it as is with below reasons: > > = > > 1) The code will complicate the crashkernel reservatoin code which > > is already difficult to understand. > > 2) It can only optimize the two cases, first is CONFIG_ZONE_DMA|DMA32 > > disabled, the other is crashkernel=3D,high is specified. While both > > two cases are corner case, most of systems have CONFIG_ZONE_DMA|DMA32 > > enabled, and most of systems have crashkernel=3DxM which is enough. > > Having them optimized won't bring benefit to most of systems. > > 3) Besides, the crashkernel=3D,high can be handled earlier because > > arm64 alwasys have memblock.bottom_up =3D=3D false currently, thus we > > don't need worry arbout the lower limit of crashkernel,high > > reservation for now. If memblock.bottom_up is set true in the future, > > this patch doesn't work any more. > > = > > = > > ... > > crash_base =3D memblock_phys_alloc_range(crash_size, CRASH_ALI= GN, > > crash_base, crash_max); > > = > > So, in my opinion, we can leave the current NON_BLOCK|SECT mapping as > > is caused by crashkernel reserving, since no regression is brought. > > And meantime, turning to check if there's any way to make the contiguous > > linear mapping and later splitting work. The patch 4, 5 in this patchset > > doesn't make much sense to me, frankly speaking. > > = > > Thanks > > Baoquan > = _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel