From patchwork Wed Aug 9 01:51:10 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Charlie Jenkins X-Patchwork-Id: 712117 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 2C53BC04A94 for ; Wed, 9 Aug 2023 01:53:18 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231183AbjHIBxR (ORCPT ); Tue, 8 Aug 2023 21:53:17 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:40516 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231263AbjHIBxP (ORCPT ); Tue, 8 Aug 2023 21:53:15 -0400 Received: from mail-pl1-x632.google.com (mail-pl1-x632.google.com [IPv6:2607:f8b0:4864:20::632]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 0EBCA1BF0 for ; Tue, 8 Aug 2023 18:53:13 -0700 (PDT) Received: by mail-pl1-x632.google.com with SMTP id d9443c01a7336-1bc73a2b0easo16668045ad.0 for ; Tue, 08 Aug 2023 18:53:13 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=rivosinc-com.20221208.gappssmtp.com; s=20221208; t=1691545992; x=1692150792; 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=2tar+fwRF9EwexnZBlGXBQ+bino7OPSUOa9FVKEDgW8=; b=FPpY5cIUXnip2ZGbpSphNOYtcmoz+9UqNCzoKTIuGrXSltzFcKRrlt8IZVpkHLRqCx OnkTugPfEWDKKQRJ75G2J1aJXt6PH8fts5QVkJJs8njOPLx6pNBBDKHzo/kPhqxS0sx3 1HU8/tEpAVmLFR+F4zwPNJwDwa/GS5jdzeVtMhkd3NlduxYlQA9dfzjF/ys4sjj6OEtk sjDMhjLy6jjBKzFs07exQfX4lKo012NsKC4Zu68gj0Uv/D7Nb/c/EwcN8oQMkTg6va+w mYmQCyjU8OGyh+PyGz8lSNWVUIf8yU596h/YkYk7J+SNhMSNxobFIMZoGtxQE5T5cv3X /BDA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20221208; t=1691545992; x=1692150792; 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=2tar+fwRF9EwexnZBlGXBQ+bino7OPSUOa9FVKEDgW8=; b=LADtlYBSG0TEVlpxK7vcOlcCopwVymWEJnlq6xhtHP/Epn8QzqpkD41Uz8UUgsmCZr jxVSL5KA/yg5WZeQkzlm+CQgWQZWYqr0zcN5Fbn4AsQvsK9XfHqSkRKsd+z37Prj/Nn/ ThyL7Q+dYWmphxiAe14fxF4ZuhyNMjd/kHCgNdEFioYk1Ej4Cf5YV0dQMpl9//msuICp bnRIPZo2S+qVOHCRvIsmJvIwKF6UN1RRHRzgaDFcmCXlBiQAEbCzgg1cgoh81w3c2CWF yH8q6TeSRJK6G5L31NRxCF5ajrxS0SribyExRknn3xgIkNDTRZaQl6M2K5/lz88h+VGl mVpQ== X-Gm-Message-State: AOJu0YyQB0MD3AgY2yLk8zYwUHlTrvOGWnijNYoxPAFGNgKjkxWDU3HL O1qKiVzaRSRkRlwMa4YiBxAKUA== X-Google-Smtp-Source: AGHT+IGZcbmVCa5ZDQZDqMBC5RXy8ZlAEnBSQVfL2GCWuQwF+OUfXTklfpU8ydkeXzNNensTQj2vcA== X-Received: by 2002:a17:903:1207:b0:1b8:6850:c3c4 with SMTP id l7-20020a170903120700b001b86850c3c4mr1594061plh.22.1691545992539; Tue, 08 Aug 2023 18:53:12 -0700 (PDT) Received: from charlie.ba.rivosinc.com ([66.220.2.162]) by smtp.gmail.com with ESMTPSA id bj7-20020a170902850700b001b87bedcc6fsm9657591plb.93.2023.08.08.18.53.11 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 08 Aug 2023 18:53:12 -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 v9 4/4] RISC-V: mm: Document mmap changes Date: Tue, 8 Aug 2023 18:51:10 -0700 Message-Id: <20230809015110.3290774-5-charlie@rivosinc.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20230809015110.3290774-1-charlie@rivosinc.com> References: <20230809015110.3290774-1-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 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.