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[2620:137:e000::1:20]) by mx.google.com with ESMTP id b26-20020a1709062b5a00b00992bfe24e47si7473788ejg.978.2023.07.13.18.38.05; Thu, 13 Jul 2023 18:38:28 -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=xExIMHzL; 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 S234536AbjGNAP0 (ORCPT + 99 others); Thu, 13 Jul 2023 20:15:26 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:40684 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233757AbjGNAPX (ORCPT ); Thu, 13 Jul 2023 20:15:23 -0400 Received: from mail-pf1-x433.google.com (mail-pf1-x433.google.com [IPv6:2607:f8b0:4864:20::433]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id EFCBD30E1 for ; Thu, 13 Jul 2023 17:15:09 -0700 (PDT) Received: by mail-pf1-x433.google.com with SMTP id d2e1a72fcca58-666e6ecb52dso927672b3a.2 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=AYpJv/KNeKHRKhKDcFRHdo3lgiYnq7xfekXuAoZM6eofz+eWTqZrkTs44aZTOr8MuS SZNZCw7qiqdzgTLOedOJgnyAjMMMRye22TkPAfnQla1e+DZQUTzxtTcXPLAQTrxr4rhl M3tc6qRBulmFS0WxDqu57ttc8LvE/v6sgsVDYzNyF1POvdwi56+nY7ekJHdP0NIZm2CT 04YOqjTGuZsB0vrNlLKiD0SzEad5mgsKZfBO6T7i+Ikadsr2OM8fQMAMraGln/d5oAYF Cz6/xkjV88/jH92W0Tw+Usc0owQXz3+armidTGgBncTy/W+KrDxqh+KVd/2B2Xf5GSvG EIdw== X-Gm-Message-State: ABy/qLYQVUxPdyKeMJBkWneJ+JnyLAQBBz/6ZBlRRgP6kq1szsIXIyhG Yx/n5iYqeDgqRAQqYnSDZngN9xQz/Q01S4w1jz0= 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 X-Spam-Status: No, score=-1.9 required=5.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,RCVD_IN_DNSWL_BLOCKED,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: 1771358082805110852 X-GMAIL-MSGID: 1771358082805110852 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.