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=-5.5 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,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 AC4B6C433E0 for ; Fri, 7 Aug 2020 16:42:23 +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 7694B20748 for ; Fri, 7 Aug 2020 16:42:23 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="ZOeqRq4A" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 7694B20748 Authentication-Results: mail.kernel.org; dmarc=none (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=HD6bZS1Cr/6FUlfpfSZO+jLjyuiTqe2co4M18Ds/yDE=; b=ZOeqRq4AH0dp4tdh9PZ7hp+fA nVqEUgEn9oUrYcRQrEPJBBb6+m9em9QGs2AkRDrngR7AADaXS0C+qkihJsf3+gPIaGbDhj5arPM6O YvLZ7/m18lQ6/dWVKBVvaFEDWiYgRhR30FK3vKPrA/Lb1wR4VXTxKO4No//lmKNtWoz47L/1HiunT oMOBG5tDyMnQHuE3Rsa5k736bxfhKMhNn+Q3iRp8OJb9ase3dZqmoZjwrqDvSHfwfIkFh6QVLPqsL GJpEXREnC5gfIc2C533/uE2GHnDnU1exaqQDTzADJa6HJHZ8Kp9LkqrX9RJpOp85FMu7WvQnlfi1v pIQzbw4GA==; Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1k45QG-0006hk-Sx; Fri, 07 Aug 2020 16:40:48 +0000 Received: from foss.arm.com ([217.140.110.172]) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1k45QD-0006gW-Ui for linux-arm-kernel@lists.infradead.org; Fri, 07 Aug 2020 16:40:46 +0000 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id AA59DD6E; Fri, 7 Aug 2020 09:40:41 -0700 (PDT) Received: from gaia (unknown [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 366A63F7D7; Fri, 7 Aug 2020 09:40:41 -0700 (PDT) Date: Fri, 7 Aug 2020 17:40:39 +0100 From: Catalin Marinas To: Derrick McKee Subject: Re: Kernel logical memory map Message-ID: <20200807164038.GN6750@gaia> References: 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-20200807_124046_052124_ABB40A24 X-CRM114-Status: GOOD ( 16.85 ) 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: linux-arm-kernel@lists.infradead.org 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 Wed, Aug 05, 2020 at 11:05:30AM -0400, Derrick McKee wrote: > In the documentation, Do you mean Documentation/arm64/memory.rst? > the first 128TB above user space is marked as > the kernel logical memory map, and I cannot find an explanation for > what that is. What is it used for? First of all, its not first above the user space. There is a very large gap between user and kernel (see the end/start values). > Can anyone point me towards further explanation of what it is used > for? It's used by the kernel to map the entire RAM. > I am looking to possibly repurpose some of that space for another use, > and I want to know if that is even possible. I wouldn't recommend it. If you need something in the kernel space (addresses starting with 0xfff...) you can look at reserving some range as we already do but you need to be a lot more specific. We have the "vmalloc" space where the kernel does various mappings for itself (e.g. ioremap). If you want to repurpose it for user, it's not really possible. This space is relies on being used in kernel space, it's not context switched (page tables pointed at by TTBR1_EL1 rather than TTBR1_EL0). However, you have enough user address space to add stuff in there. -- Catalin _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel