From patchwork Sat Jul 8 01:11:35 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Charlie Jenkins X-Patchwork-Id: 700696 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 AF2E9EB64D9 for ; Sat, 8 Jul 2023 01:12:30 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232916AbjGHBM3 (ORCPT ); Fri, 7 Jul 2023 21:12:29 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59500 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232073AbjGHBMY (ORCPT ); Fri, 7 Jul 2023 21:12:24 -0400 Received: from mail-oo1-xc2f.google.com (mail-oo1-xc2f.google.com [IPv6:2607:f8b0:4864:20::c2f]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 181962128 for ; Fri, 7 Jul 2023 18:12:23 -0700 (PDT) Received: by mail-oo1-xc2f.google.com with SMTP id 006d021491bc7-56661fe27cbso1820752eaf.3 for ; Fri, 07 Jul 2023 18:12:23 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=rivosinc-com.20221208.gappssmtp.com; s=20221208; t=1688778742; x=1691370742; 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=HbN8vPNRnpC2rsql2yMQGj4/q3r+GbD6Fgm8kHqgv+g=; b=YFsN5teo2Xz7zOmpo4/u8q+vpC9gfozaUxki8nVKZv9U3t07rRrfE2F4D/Mpc5IR6Y g2mhkupBGRVRoam4tBIlKDHh9QI3CglQEfd+e5rWKmh2SSW1KWTgyeQZWx33sFhEiL/R zgEzQmy2w6g0b6bkpsyL0pXxNONEUqIbqM5EyF7yTZ4nd+QmM5x5KgzeZtipCgrkcwup nNVAWTBHg56PkxtsUwaVwvwNubSbZIkurOLzlb3ihhEr/nv+HyjB0A54Sr6SdIfOKJ3r u1doM0X8jjfji3no8jcXuswWv7vTaFA/xQIWTftyN61BawJxTM4bORzaV5IG40o6TLK3 Hpeg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20221208; t=1688778742; x=1691370742; 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=HbN8vPNRnpC2rsql2yMQGj4/q3r+GbD6Fgm8kHqgv+g=; b=SxgmIYc0+B+lcZ89yY7EYQGpN9Lwyk12/mZOLzcLFwWZmSZoVod2V1gjIck4wxyMg/ 5ybqm/NSDlmeOgCWE4cMDsCPrWibecfVkVVBaAq9H53X6LG9qw7CyDSmAP07ZJlt97Qo veMEVs24jJCD2XvWLBkOLyNuHQm5sonAr21hok9d2XzBKPYUyXoZzVeiktfEQPBZOx7G E1t/NMv05fxEPnfaZhUyUQrqI9pzFW4XAfrEWyL6V6BfPrTLIEUEf5m1ZZLWtPXkaGM+ 8lTju4dARr8MolQpzL68xVzoNhVSkZpWR8vUkLSkwJ42D50i7MtI/F1lCahHq9R4mD9p P2jg== X-Gm-Message-State: ABy/qLYqbCpYFqyBz4m8jTQze/Kt/zE1I21Dink9ulnx30700ft6Te0E YU99WNFnc/iO+NZkws3Kewa2Ww== X-Google-Smtp-Source: APBJJlGdindojK5i23bHPXGUqY/0vPqfcqx7SQxTQvxyGmC/pEljPyl1GkowwHsZX51mLjvN1LEySQ== X-Received: by 2002:a05:6358:2925:b0:125:a552:4389 with SMTP id y37-20020a056358292500b00125a5524389mr7496248rwb.22.1688778742292; Fri, 07 Jul 2023 18:12:22 -0700 (PDT) Received: from charlie.ba.rivosinc.com ([66.220.2.162]) by smtp.gmail.com with ESMTPSA id x24-20020a170902b41800b001b87d3e845bsm3830654plr.149.2023.07.07.18.12.21 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 07 Jul 2023 18:12:21 -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 Subject: [PATCH v4 4/4] RISC-V: mm: Document mmap changes Date: Fri, 7 Jul 2023 18:11:35 -0700 Message-ID: <20230708011156.2697409-5-charlie@rivosinc.com> X-Mailer: git-send-email 2.41.0 In-Reply-To: <20230708011156.2697409-1-charlie@rivosinc.com> References: <20230708011156.2697409-1-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..8141addbf888 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 other 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.