From patchwork Wed Aug 9 23:22:04 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Charlie Jenkins X-Patchwork-Id: 712100 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 976B2C04FE1 for ; Wed, 9 Aug 2023 23:24:33 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232647AbjHIXYc (ORCPT ); Wed, 9 Aug 2023 19:24:32 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:50142 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232260AbjHIXYa (ORCPT ); Wed, 9 Aug 2023 19:24:30 -0400 Received: from mail-pf1-x432.google.com (mail-pf1-x432.google.com [IPv6:2607:f8b0:4864:20::432]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 876F71FC2 for ; Wed, 9 Aug 2023 16:24:27 -0700 (PDT) Received: by mail-pf1-x432.google.com with SMTP id d2e1a72fcca58-686daaa5f1fso243006b3a.3 for ; Wed, 09 Aug 2023 16:24:27 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=rivosinc-com.20221208.gappssmtp.com; s=20221208; t=1691623467; x=1692228267; 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=qdQX3WNwo4sWt4WkjKnJ08HLG31URbRoXVf7H5AnZ3n4OTaa437cOko2jjYggYBNx3 Uqtl8hjdOaQ5sFdI1pNdsg5WlvudRipmfEHH3jC3kSBPVvsl7sDCBIi9hJH3htjd+Scj +x4lyW8BfGjDQRdW6mPcEQh967lWkyY2MfrU8iYYuoqSur4+c4vzP8UjeTWZVpmWsXTi GrPLP1dKdTJl7/hWM1px5eML9DIPSblOF40Phwg5YuT2IX5LPipDqccZemKALDv8ntos VpDwK38TgYbp1DMAPUyfGhk2yDGhNkoAIbI8xAeXULhQkWloI08NyYlwSj+DJ7tiDJ+v bzLg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20221208; t=1691623467; x=1692228267; 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=C4lNToGBdVfrUQH4anUy3yzDqCjXu6646W5zsReYo8aeLh7iJLDFMN8F5waL1auSqV wGZ9wU6cycNRJGdfQBvXI+GFubz1kNWCbimvKCJN4pfpG2ON8sys2/NvCBQ+k7zqP0IN LKn+Oaopi1/F1nWk1DsqjZTKFGfHElDU19sxGDfhl5Y62Ezpt5eyPhNWW/nxd6a2EUjZ 3W8wZVxLQCS6mi4sGT/pv7zS6YKSj/p/vXy4plVl/cC9SFmwIqU/P/VdjK9WeSP51wuS i+jo2016nrCNr2Xw2E2gH6cKXdnU/nksIrmWzzYdqoz25gG8NiUm7IVi1N4K7nn2SKuf 5PzQ== X-Gm-Message-State: AOJu0YwEp545VkM4b7skFztXlM1GoNzc0OLQw5ih8GiC0KgG8MqFnS/M FqSa6hqRwnVE4qaLCS5E3lYHJw== X-Google-Smtp-Source: AGHT+IHPggFTtnxabsF/jkLvnF3G7KP5USE4CizFGjoAWFxir/OOf3x64PmOQQ970Z2IhxBU3MEknw== X-Received: by 2002:a05:6a20:12c2:b0:131:4808:d5a1 with SMTP id v2-20020a056a2012c200b001314808d5a1mr781717pzg.28.1691623467045; Wed, 09 Aug 2023 16:24:27 -0700 (PDT) Received: from charlie.ba.rivosinc.com ([66.220.2.162]) by smtp.gmail.com with ESMTPSA id l18-20020a170902d35200b001b54d064a4bsm82765plk.259.2023.08.09.16.24.25 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 09 Aug 2023 16:24:26 -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 v10 4/4] RISC-V: mm: Document mmap changes Date: Wed, 9 Aug 2023 16:22:04 -0700 Message-ID: <20230809232218.849726-5-charlie@rivosinc.com> X-Mailer: git-send-email 2.41.0 In-Reply-To: <20230809232218.849726-1-charlie@rivosinc.com> References: <20230809232218.849726-1-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.