From patchwork Fri Jul 14 16:54:52 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Charlie Jenkins X-Patchwork-Id: 703453 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 AF266EB64DC for ; Fri, 14 Jul 2023 16:56:06 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236142AbjGNQ4F (ORCPT ); Fri, 14 Jul 2023 12:56:05 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:34240 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236163AbjGNQ4D (ORCPT ); Fri, 14 Jul 2023 12:56:03 -0400 Received: from mail-pl1-x631.google.com (mail-pl1-x631.google.com [IPv6:2607:f8b0:4864:20::631]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id BADB935AC for ; Fri, 14 Jul 2023 09:56:01 -0700 (PDT) Received: by mail-pl1-x631.google.com with SMTP id d9443c01a7336-1b8a462e0b0so13039695ad.3 for ; Fri, 14 Jul 2023 09:56:01 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=rivosinc-com.20221208.gappssmtp.com; s=20221208; t=1689353761; x=1689958561; 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=ECP+dufnQHsYRxuqgPOTnUSVvIo4ePBLAYzcr/uPu+86xHXRbq559fnQxM4loYgYii 9q/1Ih5sS/4Nz4IV5XKxNs5M7eNK2wNCyxQPv1SoVXWcMmwbEpzI74Jdn1u5Cczfadul jSHTTTzLM34mcqiVS7oXLHnW//LVLHHdygX3s6M81zVFp+Lmjk+KCS/Jt+2NFtsSEwsS hM2QAfrxJ4G7EMIqqaMGTDm7wAokuRc+ct0d85q54+SDh5Xc1EJl+Md33rZrNOHTixiq BSKIqdZJu/lQ2SebCzY5jdSZwDdpY3w9ELYszKlZ96Lgs1OHBPPpkiA+q8wz6OTq9PHQ LbBw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20221208; t=1689353761; x=1689958561; 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=daULb7ZleH3HoPDsBjuCn9sXk5bWiMy3OZsnfwOInKA6Cp4OmiEH42cP9pVGFgYCQE sxyh33wXbGsffv+ae61Or2Amxk53kHtTU9vd9S+USyzcSAF3AnPnncfiPYdmgS2r89Fb lHD6nyUeNYLrRcxx/uHKEy1lj5gMUVMYMzXacYKGUhgO1YOBHwjFbtHi+PhJQnoS1vAq 4uKl6IFicwm3lHAw7ZfRE61Tk3wm+Qt0jdsntDznSamPFE0zJvUpA8Z/EGVf0Iab/r5H eFCevOjBknr5YaX0mXgfAYsFvCN5fNAJInpSFv9FlmcOrYDT0aWStJQScvBE9UtzBKqC nXoA== X-Gm-Message-State: ABy/qLZvs6D4cGvowNlNawlKSG/qK6ZpyESdyGlgR9ls40VslnqcfYEd 5mdDAs0QvfHWeALjFP5pfQDJcA== X-Google-Smtp-Source: APBJJlFsvoNdVZTC5wGAHNOb7OEsPFjJFgSI3IvikXJ3ahp3VMzgfUgYU2kfHESUML2FBAHGPHaiUA== X-Received: by 2002:a17:903:1248:b0:1b3:d11c:23ca with SMTP id u8-20020a170903124800b001b3d11c23camr4729934plh.8.1689353761143; Fri, 14 Jul 2023 09:56:01 -0700 (PDT) Received: from charlie.ba.rivosinc.com ([66.220.2.162]) by smtp.gmail.com with ESMTPSA id s8-20020a170902b18800b001b694140d96sm8008081plr.170.2023.07.14.09.55.59 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 14 Jul 2023 09:56:00 -0700 (PDT) From: Charlie Jenkins To: linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.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 v6 4/4] RISC-V: mm: Document mmap changes Date: Fri, 14 Jul 2023 09:54:52 -0700 Message-ID: <20230714165508.94561-5-charlie@rivosinc.com> X-Mailer: git-send-email 2.41.0 In-Reply-To: <20230714165508.94561-1-charlie@rivosinc.com> References: <20230714165508.94561-1-charlie@rivosinc.com> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-kselftest@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.