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[2620:137:e000::1:20]) by mx.google.com with ESMTP id bt22-20020a056a00439600b006848418206csi1853838pfb.190.2023.07.27.14.51.50; Thu, 27 Jul 2023 14:52:03 -0700 (PDT) Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20; Authentication-Results: mx.google.com; dkim=pass header.i=@rivosinc-com.20221208.gappssmtp.com header.s=20221208 header.b=O0RhQf8K; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231890AbjG0V1L (ORCPT + 99 others); Thu, 27 Jul 2023 17:27:11 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51074 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230118AbjG0V06 (ORCPT ); Thu, 27 Jul 2023 17:26:58 -0400 Received: from mail-pf1-x42b.google.com (mail-pf1-x42b.google.com [IPv6:2607:f8b0:4864:20::42b]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 172851BC6 for ; Thu, 27 Jul 2023 14:26:57 -0700 (PDT) Received: by mail-pf1-x42b.google.com with SMTP id d2e1a72fcca58-686ba29ccb1so899417b3a.1 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=G7oczf4TNtQsSkJ7Sh8Tt4pDkbKDabQ+vf6i8HJV8AOKKhrj0XESZQgzU1XeYzW/NT cwnNJkfL3sqkzrrOgw6Wd1ApHFtOau75WMkPrNyToLiDuFoBSwsB9zJK6Q+bfyajBUfb r74z2OpieETpajkVoY3e0cgpEsoRDZZca1BhD8NgX5kKnvEX8DuQ0a9RtthDay9CX1L3 HGN5hEFQrgsAETbok29zTRKeTjYKLjesF7NtMOdat7rnPLZuiZ1Sim5wb7tGIMVpBYPr KlfNCBIKmgKTMkowFJQwKjHn78E60ZXsgB5gFsgHbUqU/zNvlVz92Dljsc8a+SJzD9wA ODAw== X-Gm-Message-State: ABy/qLZyvXIxpo7sKz3+vOjFWJoYncKeARhb0gXuv7K3e02CFpClpSZ3 tWuo4aauAUFKIJC1XYXk7eFdnw== 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 X-Spam-Status: No, score=-1.9 required=5.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,RCVD_IN_DNSWL_NONE,SPF_HELO_NONE,SPF_PASS, T_SCC_BODY_TEXT_LINE autolearn=unavailable autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org X-getmail-retrieved-from-mailbox: INBOX X-GMAIL-THRID: 1772612195056084611 X-GMAIL-MSGID: 1772612195056084611 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 Reviewed-by: Alexandre Ghiti --- 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.