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=-5.3 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, NICE_REPLY_A,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 2D5AEC433DF for ; Wed, 14 Oct 2020 03:46:55 +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 70C13215A4 for ; Wed, 14 Oct 2020 03:46:54 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="CBsI8+Uw" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 70C13215A4 Authentication-Results: mail.kernel.org; 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Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1kSXix-0002n4-CT; Wed, 14 Oct 2020 03:45:11 +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 1kSXiu-0002ma-4z for linux-arm-kernel@lists.infradead.org; Wed, 14 Oct 2020 03:45:09 +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 9BF3D31B; Tue, 13 Oct 2020 20:45:04 -0700 (PDT) Received: from [10.163.76.91] (unknown [10.163.76.91]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id BA6A63F73C; Tue, 13 Oct 2020 20:45:02 -0700 (PDT) Subject: Re: [PATCH v2 2/4] arm64: mm: extend linear region for 52-bit VA configurations To: Ard Biesheuvel , linux-arm-kernel@lists.infradead.org References: <20201008153602.9467-1-ardb@kernel.org> <20201008153602.9467-3-ardb@kernel.org> From: Anshuman Khandual Message-ID: Date: Wed, 14 Oct 2020 09:14:33 +0530 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: <20201008153602.9467-3-ardb@kernel.org> Content-Language: en-US X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20201013_234508_306392_12ED22C4 X-CRM114-Status: GOOD ( 16.54 ) 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: catalin.marinas@arm.com, will@kernel.org, Steve Capper 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 10/08/2020 09:06 PM, Ard Biesheuvel wrote: > For historical reasons, the arm64 kernel VA space is configured as two > equally sized halves, i.e., on a 48-bit VA build, the VA space is split > into a 47-bit vmalloc region and a 47-bit linear region. > > When support for 52-bit virtual addressing was added, this equal split > was kept, resulting in a substantial waste of virtual address space in > the linear region: > > 48-bit VA 52-bit VA > 0xffff_ffff_ffff_ffff +-------------+ +-------------+ > | vmalloc | | vmalloc | > 0xffff_8000_0000_0000 +-------------+ _PAGE_END(48) +-------------+ > | linear | : : > 0xffff_0000_0000_0000 +-------------+ : : > : : : : > : : : : > : : : : > : : : currently : > : unusable : : : > : : : unused : > : by : : : > : : : : > : hardware : : : > : : : : > 0xfff8_0000_0000_0000 : : _PAGE_END(52) +-------------+ > : : | | > : : | | > : : | | > : : | | > : : | | > : unusable : | | > : : | linear | > : by : | | > : : | region | > : hardware : | | > : : | | > : : | | > : : | | > : : | | > : : | | > : : | | > 0xfff0_0000_0000_0000 +-------------+ PAGE_OFFSET +-------------+ > > As illustrated above, the 52-bit VA kernel uses 47 bits for the vmalloc > space (as before), to ensure that a single 64k granule kernel image can > support any 64k granule capable system, regardless of whether it supports > the 52-bit virtual addressing extension. However, due to the fact that > the VA space is still split in equal halves, the linear region is only > 2^51 bytes in size, wasting almost half of the 52-bit VA space. Right, that is a huge wastage. Increasing the linear mapping will definitely help in getting more memory used on the system. But now do we have enough vmemmap range to support this enlarged linear mapping ? _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel