From patchwork Thu Jul 27 21:26:29 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Charlie Jenkins X-Patchwork-Id: 707269 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 47C46C00528 for ; Thu, 27 Jul 2023 21:27:05 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231489AbjG0V1C (ORCPT ); Thu, 27 Jul 2023 17:27:02 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51018 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229528AbjG0V06 (ORCPT ); Thu, 27 Jul 2023 17:26:58 -0400 Received: from mail-pf1-x429.google.com (mail-pf1-x429.google.com [IPv6:2607:f8b0:4864:20::429]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 175931BF4 for ; Thu, 27 Jul 2023 14:26:57 -0700 (PDT) Received: by mail-pf1-x429.google.com with SMTP id d2e1a72fcca58-686f94328a4so634105b3a.0 for ; Thu, 27 Jul 2023 14:26:57 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=rivosinc-com.20221208.gappssmtp.com; s=20221208; t=1690493216; x=1691098016; 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=gcvGxWKs0ioHSwaNFVtuDJQ1B/8SpZlsoy8QXz36r7I=; b=O0RhQf8KfE7AkPva40tWc9J+su1HI1UE2kEfdz7pkwxir6Zk97X4vA7+YDbYbExjNZ 4RyRTkXeeZg8c5H4DsdkNwy5z0Oc/dOtYSntC5cuj+IHiZcJVOOl/pSPl7D3Ihdgfc6g IPIa1TkeHGbit0ypGybX6xXCaiyifj2oUvQhzSw14P8D1lwo9LkNq8obIlWu0dEXqnfq NOq9monYfeRcCg+StWnRJrEbiF6xrTEIpjpHi2DRzaZs15+pTwpPDnYlfAInaRS4UyKP klrItNmQI+SFf7u8/3WOJRIz/cZ031FyXJArV/48cx9URntu/5ar9hUBmNCWWhDXMrQw OqJA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20221208; t=1690493216; x=1691098016; 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=gcvGxWKs0ioHSwaNFVtuDJQ1B/8SpZlsoy8QXz36r7I=; b=ZcrCYx+yNYR+NsRX10dlx9B0qV//KcSpHVnkXTawSLsnnxAAuLE/g4sNb+qHmAJ3Vu S39y58gabBYdFLH/2r5j990/ShdJUCj79jt1qlkafIFxxuGkDYt49WkimvPb68ASrKOQ b40q8njxGcb8cy5qmVY56Wtn76KpukWzqhtNrCo4APXbLkK4UxeCoMiHrynmyzt0B1Ti bxmaZPwLcODycbX6LuRfy4Yhl1dB9FZyAcGMBuu+nM7+KUoPfYIPcKtQDdjGHi0pmzwK RU45o3IFcPMkZHO8gJYf8RGLEpTE3+Cf/0H48vjlRXCT40iRLV3+tlUOrLvjRk9GFYWm Mppw== X-Gm-Message-State: ABy/qLYFamWgK8gcoV+t2/pioa1S/MAN4SO4BC+DuF6/D030BaeSzFGh KwIo4O5Y03BPq1E2Uh6mFxMVfg== X-Google-Smtp-Source: APBJJlFlY+9HLXpB5MOpoEilud+PtI86fX/t6QctT4gfhpPOy7817Igg+eQtg4O7iE22xtMxf1LQKw== X-Received: by 2002:a05:6a21:3984:b0:12f:d350:8a12 with SMTP id ad4-20020a056a21398400b0012fd3508a12mr467624pzc.21.1690493216617; Thu, 27 Jul 2023 14:26:56 -0700 (PDT) Received: from charlie.ba.rivosinc.com ([66.220.2.162]) by smtp.gmail.com with ESMTPSA id c5-20020aa78c05000000b00682562b1549sm1912312pfd.24.2023.07.27.14.26.55 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 27 Jul 2023 14:26:56 -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 v8 4/4] RISC-V: mm: Document mmap changes Date: Thu, 27 Jul 2023 14:26:29 -0700 Message-ID: <20230727212647.4182407-5-charlie@rivosinc.com> X-Mailer: git-send-email 2.41.0 In-Reply-To: <20230727212647.4182407-1-charlie@rivosinc.com> References: <20230727212647.4182407-1-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..69ff6da1dbf8 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 hint address passed to mmap will cause the largest +address space that fits entirely into the hint to be used, 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 << 47` must be provided. Note that this is 47 due to sv48 userspace +ending at :code:`1 << 47` 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 << 56` must be provided.