From patchwork Wed Jul 26 16:45:58 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Charlie Jenkins X-Patchwork-Id: 707294 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 3CA22C001B0 for ; Wed, 26 Jul 2023 16:46:56 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231917AbjGZQqz (ORCPT ); Wed, 26 Jul 2023 12:46:55 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:33310 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231172AbjGZQqm (ORCPT ); Wed, 26 Jul 2023 12:46:42 -0400 Received: from mail-pl1-x631.google.com (mail-pl1-x631.google.com [IPv6:2607:f8b0:4864:20::631]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 88DC02703 for ; Wed, 26 Jul 2023 09:46:35 -0700 (PDT) Received: by mail-pl1-x631.google.com with SMTP id d9443c01a7336-1bb775625e2so8481965ad.1 for ; Wed, 26 Jul 2023 09:46:35 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=rivosinc-com.20221208.gappssmtp.com; s=20221208; t=1690389995; x=1690994795; 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=ctlEmW7DMTMNY+Sp7acXqqDtGLdfH554pjXRJaq8fLvxFb/RtQTWgjya5aX8frZUG+ kWLLX3V5bkPJ8D9sRUV/MwHTEJpB9RCwH6/ndhkksdQtRuU+HRr0zUfscDgxiFSHZA9+ yIU0ZD4Tam8mQ2WS+5pLZ/c5X4RhjfmHJo3MwLkOOIWTzwMnMBP8Q0wn+W52egZzi2xU AAyOixs1odiPKZLEKGezwwzYUkbE2yPosL+ri5v70wHRzK4oQvk1fggscCcK6icuFnGe uL29fxGA2FdvaKyJUxHyjHp+jMTQA1xrvEzeIai5Rjkq71aK2LAAFsldGh/eFZfk8xRM s+hg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20221208; t=1690389995; x=1690994795; 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=mGm09s0SwS3e3i7hCn95QySBHEylAu8/SwJQihK07rz93L7CJPj5Or5woxzG9enmEy ldvK1RdfWxyEJmmVX4KmcCToJIlAGt5lEEgnD9/bYUD0MpV+sFxmtuvf1fgdxxHTZmVt HVSgBxCwiXrONVdFb6P28uqHvc07Tkq6F88hL/eiGHBed1MiDheSPVtxhPYG54rsgtn4 feEVi+pWt+OkhoI4Sr8c7XC/n0bUHaUJzRN/PYOv0pFYpToB5H6HnILYM7OyacPZW37n 4X2/TxboOUoRIS8MFa0aI0I5joc8OcoZjS352i+EpZ4cilmmrsnOXX8ChssTFsR8J0mY 7/hQ== X-Gm-Message-State: ABy/qLZ7SmL3LHAkgpCj45rGW2e4BvnZrMJaWCMSx/C9YR6Ejp967uwm wTuV8brFANBW7AeDgYI3V+W8Cg== X-Google-Smtp-Source: APBJJlHYD5X46sfJHvjFJ8cY7MrqSJBPdDrgEnmRM7T9AiO1YpDySEyimp6MxA9+6dubMdyjQlpBgQ== X-Received: by 2002:a17:902:c943:b0:1b2:676d:1143 with SMTP id i3-20020a170902c94300b001b2676d1143mr38193pla.15.1690389994874; Wed, 26 Jul 2023 09:46:34 -0700 (PDT) Received: from charlie.ba.rivosinc.com ([66.220.2.162]) by smtp.gmail.com with ESMTPSA id h5-20020a170902f54500b001bb6c5ff4edsm11628870plf.173.2023.07.26.09.46.33 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 26 Jul 2023 09:46:34 -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 v7 4/4] RISC-V: mm: Document mmap changes Date: Wed, 26 Jul 2023 09:45:58 -0700 Message-ID: <20230726164620.717288-5-charlie@rivosinc.com> X-Mailer: git-send-email 2.41.0 In-Reply-To: <20230726164620.717288-1-charlie@rivosinc.com> References: <20230726164620.717288-1-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.