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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 90DDAC001DE for ; Fri, 14 Jul 2023 00:15:25 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234296AbjGNAPY (ORCPT ); Thu, 13 Jul 2023 20:15:24 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:40592 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234567AbjGNAPV (ORCPT ); Thu, 13 Jul 2023 20:15:21 -0400 Received: from mail-pf1-x436.google.com (mail-pf1-x436.google.com [IPv6:2607:f8b0:4864:20::436]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 7313930D8 for ; Thu, 13 Jul 2023 17:15:09 -0700 (PDT) Received: by mail-pf1-x436.google.com with SMTP id d2e1a72fcca58-6687096c6ddso946707b3a.0 for ; Thu, 13 Jul 2023 17:15:09 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=rivosinc-com.20221208.gappssmtp.com; s=20221208; t=1689293709; x=1689898509; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:from:to:cc:subject:date :message-id:reply-to; bh=iY0BqE22+vH8ihdQ5F+U3lQTo4OY0Ve5Zo6wbRWfHfc=; b=xExIMHzLTtkjN2LFQngS3OX4jDs1xLdIX7r/tiDx0kppQfQRkPMYGwyfuGwrBTa86a XoaNrcUcmG5pmtq3t+bqbkNwiHPqfObctew9lUGCvXVSRZ5ZMzwxuDl5bh0kXZqCOeN/ 2KOkMuhJYkV6QfPobPU9mX56qewrBddlJ17DJjsRmikAwwn6WVy6MHjfUpM665kqgqnx 8Vd77tSJfClsrB+dbBunC3han9WPucnmhgEbe2AxB1x5RWqedcL/TQmo7JAbJuXl1Q+J +JuGlcjr4IzBotD3ZK9zOhKx+93UelIHVMWCiiWjS83cS6p52MDULRTAs1+X2jnehbH9 5cQw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20221208; t=1689293709; x=1689898509; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=iY0BqE22+vH8ihdQ5F+U3lQTo4OY0Ve5Zo6wbRWfHfc=; b=lhSWpxFx+rqGYUc12dRk87yuyk5b00yUYnbSqsfYqvrmpPwHIFgedx53exsYTuPs4a QnJ6QvuWVacgw9InVzMRPQ0FitJXibGg6nazKLJX1euL25pSpAdjeUER509UYswkw+3h wKQsQCIiqfQUXFbNVsVD3HULSQCv1jLVLjf5qgcNRdF5819dPB6kjk4uucK7prFxBcTn A7iaLc3Sdsw2xogh6P3r8aR2yX5wV4cKgtrlV/DVEDLhEkj4ViPMYvJ/ka1ykaqRYxNU 88dyJEZ0GVF1lp89C5r9D4tkL5SOW6zPdyzfHQ+lGjINFAfTSZBEfQoen35mT7NRgDt2 L0Jg== X-Gm-Message-State: ABy/qLbhoQmVc8ZNEDX5E1ywFcfdCsOaS186RzmYWRkSoLni3YZ1gkQW PDrPAZrRWdpcMoYGuMLbs2yNdQ== X-Google-Smtp-Source: APBJJlE/NehJK/yZ31QQ51ruFcoOUZ8Dr5gN8omHKM50vUTZXpJ3oVnR2nhUcvBJtDwEUljTcHiqAg== X-Received: by 2002:a05:6a00:2d84:b0:666:8cbb:6e0f with SMTP id fb4-20020a056a002d8400b006668cbb6e0fmr3042793pfb.3.1689293708687; Thu, 13 Jul 2023 17:15:08 -0700 (PDT) Received: from charlie.ba.rivosinc.com ([66.220.2.162]) by smtp.gmail.com with ESMTPSA id x25-20020aa793b9000000b00673e652985esm5938107pff.44.2023.07.13.17.15.07 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 13 Jul 2023 17:15:08 -0700 (PDT) From: Charlie Jenkins To: linux-kernel@vger.kernel.org, linux-riscv@lists.infradead.org Cc: charlie@rivosinc.com, conor@kernel.org, paul.walmsley@sifive.com, palmer@rivosinc.com, aou@eecs.berkeley.edu, anup@brainfault.org, konstantin@linuxfoundation.org, linux-doc@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-mm@kvack.org, mick@ics.forth.gr, jrtc27@jrtc27.com, rdunlap@infradead.org, alexghiti@rivosinc.com Subject: [PATCH v5 4/4] RISC-V: mm: Document mmap changes Date: Thu, 13 Jul 2023 17:14:03 -0700 Message-ID: <20230714001430.75798-5-charlie@rivosinc.com> X-Mailer: git-send-email 2.41.0 In-Reply-To: <20230714001430.75798-1-charlie@rivosinc.com> References: <20230714001430.75798-1-charlie@rivosinc.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-doc@vger.kernel.org The behavior of mmap is modified with this patch series, so explain the changes to the mmap hint address behavior. Signed-off-by: Charlie Jenkins --- Documentation/riscv/vm-layout.rst | 22 ++++++++++++++++++++++ 1 file changed, 22 insertions(+) diff --git a/Documentation/riscv/vm-layout.rst b/Documentation/riscv/vm-layout.rst index 5462c84f4723..892412b91300 100644 --- a/Documentation/riscv/vm-layout.rst +++ b/Documentation/riscv/vm-layout.rst @@ -133,3 +133,25 @@ RISC-V Linux Kernel SV57 ffffffff00000000 | -4 GB | ffffffff7fffffff | 2 GB | modules, BPF ffffffff80000000 | -2 GB | ffffffffffffffff | 2 GB | kernel __________________|____________|__________________|_________|____________________________________________________________ + + +Userspace VAs +-------------------- +To maintain compatibility with software that relies on the VA space with a +maximum of 48 bits the kernel will, by default, return virtual addresses to +userspace from a 48-bit range (sv48). This default behavior is achieved by +passing 0 into the hint address parameter of mmap. On CPUs with an address space +smaller than sv48, the CPU maximum supported address space will be the default. + +Software can "opt-in" to receiving VAs from another VA space by providing +a hint address to mmap. A call to mmap is guaranteed to return an address +that will not override the unset left-aligned bits in the hint address, +unless there is no space left in the address space. If there is no space +available in the requested address space, an address in the next smallest +available address space will be returned. + +For example, in order to obtain 48-bit VA space, a hint address greater than +:code:`1 << 38` must be provided. Note that this is 38 due to sv39 userspace +ending at :code:`1 << 38` and the addresses beyond this are reserved for the +kernel. Similarly, to obtain 57-bit VA space addresses, a hint address greater +than or equal to :code:`1 << 47` must be provided. -- 2.41.0