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 X-Spam-Level: X-Spam-Status: No, score=-5.2 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 19B05C433DF for ; Mon, 12 Oct 2020 16:24:14 +0000 (UTC) Received: from merlin.infradead.org (merlin.infradead.org [205.233.59.134]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id BF0F9206CB for ; Mon, 12 Oct 2020 16:24:13 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="sTpBYCsI" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org BF0F9206CB Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=merlin.20170209; h=Sender:Content-Transfer-Encoding: Content-Type:Cc:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References:Message-ID: Subject: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=uc0tB/MO5OSIE7EGyIlP9lP94a70JGhqjGqm1hKcGVE=; b=sTpBYCsIEWsEhbp149osIcQVT zUsqzYj6fHBeRpKJFX6DXMbS7KkGnbOBm5leKnD1pUmXhV5YQeDqrGTUr9D8kWmJgGhvfRmtmEJM0 h8HVk2gtdRIgpWYvbxVAntgF1P96ZXIvua3s9C0VYlIN+V7vkXvwaEMwQ1Pw8plNGNFdLSVQSo3M0 sud5vWxHHmV40wOqLNBi9/1SXKX6Ju5vDMZwy6UJCKLFS+9c53Qn2gRG3sKTH3qsfHu+z+iXvySip gAg3JwUQdR9FOtin9Khr+55PXJU2APex+7bnRtPtcLhLVIb22ZW+4YEv1jSOfk4q/Sc1wCfj77VWG tDQqjlyeg==; Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1kS0b1-0001Fb-5T; Mon, 12 Oct 2020 16:22:47 +0000 Received: from mail.kernel.org ([198.145.29.99]) by merlin.infradead.org with esmtps (Exim 4.92.3 #3 (Red Hat Linux)) id 1kS0ay-0001Er-DM for linux-arm-kernel@lists.infradead.org; Mon, 12 Oct 2020 16:22:45 +0000 Received: from gaia (unknown [95.149.105.49]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 6D7A5206CB; Mon, 12 Oct 2020 16:22:41 +0000 (UTC) Date: Mon, 12 Oct 2020 17:22:39 +0100 From: Catalin Marinas To: Ard Biesheuvel Subject: Re: [PATCH] arm64: mm: set ZONE_DMA size based on early IORT scan Message-ID: <20201012162238.GC6493@gaia> References: <20201010093153.30177-1-ardb@kernel.org> <20201012092821.GB9844@gaia> <20201012112453.GD9844@gaia> <20201012154954.GB6493@gaia> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20201012_122244_577219_20D55E3C X-CRM114-Status: GOOD ( 25.82 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Lorenzo Pieralisi , Anshuman Khandual , Robin Murphy , Sudeep Holla , Jeremy Linton , ACPI Devel Maling List , Rob Herring , Linux ARM , Hanjun Guo , Will Deacon , Christoph Hellwig , Nicolas Saenz Julienne 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 Mon, Oct 12, 2020 at 05:55:45PM +0200, Ard Biesheuvel wrote: > On Mon, 12 Oct 2020 at 17:50, Catalin Marinas wrote: > > > > On Mon, Oct 12, 2020 at 12:43:05PM +0200, Ard Biesheuvel wrote: > > > > > Also, could someone give an executive summary of why it matters where > > > > > the crashkernel is loaded? As far as I can tell, reserve_crashkernel() > > > > > only allocates memory for the kernel's executable image itself, which > > > > > can usually be loaded anywhere in memory. I could see how a > > > > > crashkernel might need some DMA'able memory if it needs to use the > > > > > hardware, but I don't think that is what is going on here. [...] > > However, the crashkernel=... range is meant for sufficiently large > > reservation to be able to run the kdump kernel, not just load the image. > > Sure. But I was referring to the requirement that it is loaded low in > memory. Unless I am misunderstanding something, all we need for the > crashkernel to be able to operate is some ZONE_DMA memory in case it > is needed by the hardware, and beyond that, it could happily live > anywhere in memory. Yes, the crash kernel doesn't need to be loaded in the low memory. But some low memory needs to end up in its perceived System RAM. That's what Chen is trying to do with this series: https://lore.kernel.org/linux-arm-kernel/20200907134745.25732-1-chenzhou10@huawei.com/ It reserves the normal crashkernel memory at some high address range with a small block (currently proposed as 256MB similar to x86) in the "low" range. This "low" range for arm64 currently means below 1GB but it's only RPi4 that needs it this low, all other platforms are fine with the full low 32-bit range. If it's not doable in a nice way, we'll just leave with this permanent 1GB ZONE_DMA and hope we won't get platforms requiring an even smaller one. There's also the option of ignoring kdump on RPi4, make ZONE_DMA depend on !CRASH_DUMP and the "low" reservations can use the full 32-bit range since the kdump kernel won't need <30-bit addresses. -- Catalin _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel