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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id D028AC433EF for ; Mon, 25 Jul 2022 06:46:17 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 373B18E0002; Mon, 25 Jul 2022 02:46:17 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 323058E0001; Mon, 25 Jul 2022 02:46:17 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 1EA408E0002; Mon, 25 Jul 2022 02:46:17 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0010.hostedemail.com [216.40.44.10]) by kanga.kvack.org (Postfix) with ESMTP id 0DA728E0001 for ; Mon, 25 Jul 2022 02:46:17 -0400 (EDT) Received: from smtpin11.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay04.hostedemail.com (Postfix) with ESMTP id D7DAC1A0400 for ; Mon, 25 Jul 2022 06:46:16 +0000 (UTC) X-FDA: 79724687952.11.5567664 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by imf27.hostedemail.com (Postfix) with ESMTP id 7381A4001E for ; Mon, 25 Jul 2022 06:46:16 +0000 (UTC) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 91D47610A1; Mon, 25 Jul 2022 06:46:15 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id DBF0EC341C7; Mon, 25 Jul 2022 06:46:09 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1658731575; bh=hIZrYAxn265ebgeF7Bwq7AWTsRMM8aNkjPhwdYrVvPo=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=osNv7G6brArIxFH6QeFgaRQ6faY2Q0HTiCZ1w/P+kGwwRNfXEJMAHrbYdJY2g1aFa qHTyjZ/CCqMxNbJd6JjQSSBfbLFbXr7PAtJKicGfARZgvm/uATPZ9KNmKkophIW5lo XdagoKwJqC3B78lYz417IQxdGlnTr/RiojJn2nBPN9GOwtJ17VSDxlkZFtfdqPlr9U BienTQy1Fcxw2C1faujgJCrzJdQXrwhaKOtLnaitvQe50I44I6mQqR+0rnwfHQk/SC iKl7uAedh7x2u8PAJqiGQnIfoII+C6ypUkQAP7GARtMT/Cd7hYryBlytp56Vh/4lqh M5fNWDCiB67rw== Date: Mon, 25 Jul 2022 09:46:04 +0300 From: Mike Rapoport To: Will Deacon Cc: "guanghui.fgh" , baolin.wang@linux.alibaba.com, catalin.marinas@arm.com, akpm@linux-foundation.org, david@redhat.com, jianyong.wu@arm.com, james.morse@arm.com, quic_qiancai@quicinc.com, christophe.leroy@csgroup.eu, jonathan@marek.ca, mark.rutland@arm.com, thunder.leizhen@huawei.com, anshuman.khandual@arm.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, geert+renesas@glider.be, ardb@kernel.org, linux-mm@kvack.org, yaohongbo@linux.alibaba.com, alikernel-developer@linux.alibaba.com Subject: Re: [PATCH v5] arm64: mm: fix linear mem mapping access performance degradation Message-ID: References: <1657460657-25698-1-git-send-email-guanghuifeng@linux.alibaba.com> <20220718131005.GA12406@willie-the-truck> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220718131005.GA12406@willie-the-truck> ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1658731576; a=rsa-sha256; cv=none; b=2gEhV1yON1avu5i5nMloyPK65UzEqxKtso3s3ymPFRcoTUVUCepTkroXarvyNqbgDAOAZm EtCPXk4QjEeDaRKzdzC7bTNqLz6YAXpQZU08dWW+2tpUBEMG99UCOOb58PtvgAIyLU4fd3 Fko8yZES8Lt8FPgm3mglfKaZSM5lr6Y= ARC-Authentication-Results: i=1; imf27.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=osNv7G6b; dmarc=pass (policy=none) header.from=kernel.org; spf=pass (imf27.hostedemail.com: domain of rppt@kernel.org designates 139.178.84.217 as permitted sender) smtp.mailfrom=rppt@kernel.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1658731576; h=from:from:sender: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: in-reply-to:in-reply-to:references:references:dkim-signature; bh=I6Pcrf1wa3c7ch0xmCEFsRTJHT6mCDfuRRjoL6HA6Uo=; b=s3iATNGy9vLN4cr6z5gKhQGXZXoBFiPfqjrEUNE4cU6YoqdfYpYM85SfcW5AflXYEp+b7W SeyvdEM6dM3BpkoQXo5/U5AhuSRfAqvZiAR/vtpDOtt38VO3z9nuuReryVeeNrMOAYyoMU EmDfwoUres/S38UJrGuSIERvsT1JKAs= Authentication-Results: imf27.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=osNv7G6b; dmarc=pass (policy=none) header.from=kernel.org; spf=pass (imf27.hostedemail.com: domain of rppt@kernel.org designates 139.178.84.217 as permitted sender) smtp.mailfrom=rppt@kernel.org X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: 7381A4001E X-Stat-Signature: 93ty1zirkg6edk78hme8amz3ersubc1r X-Rspam-User: X-HE-Tag: 1658731576-626801 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Mon, Jul 18, 2022 at 02:10:06PM +0100, Will Deacon wrote: > On Sun, Jul 10, 2022 at 11:33:02PM +0800, guanghui.fgh wrote: > > In short, this path work: > > > > 1.Before doing work for rebuiling crashkernel mem, the pgd is swapper_pg_dir > > in [[[ttbr1]]] > > > > 2.Change the [[[ttbr0]]]to use idmap_pg_dir pgd > > > > 3.The [[[idmap_cpu_replace_ttbr1_with_flush_tlb]]] are mapped [[[only]]] > > with idmap_pg_dir mapping in [[[ttbr0]]] > > > > 4.The [[[idmap_cpu_replace_ttbr1_with_flush_tlb]]] will flush tlb all, > > switch [[[ttbr1]]] to use init_pg_dir pgd(and flush tlb all again). > > There is no tlb conflict to swapper_pg_dir. > > There is no tlb cache for swapper_pg_dir. > > > > 5.Woring with init_pg_dir pgd to access swapper_pg_dir pagetable with fix > > mapping. And modify crashkernel mapping in the swapper_pg_dir without any > > tlb conflict and flush. > > > > 6.When finishing the work, switch ttbr1 pgd to the origin swapper_pg_dir > > with cpu_replace_ttbr1 function(similar to the above). > > I do not think that this complexity is justified. As I have stated on > numerous occasions already, I would prefer that we leave the crashkernel > mapped when rodata is not "full". That fixes your performance issue and > matches what we do for module code, so I do not see a security argument > against it. The protection of the crash kernel is not about security. This is about an ability to do post mortem with kdump and such when the things go awry. I think it's possible to have both large pages in the linear map and the protection of crash kernel in much simpler way that this patch does, I'll try to send an RFC Really Soon. > I do not plan to merge this patch as-is. > > Thanks, > > Will -- Sincerely yours, Mike.