From mboxrd@z Thu Jan 1 00:00:00 1970 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 613FFC0015E for ; Sun, 6 Aug 2023 10:09:06 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230220AbjHFKJE (ORCPT ); Sun, 6 Aug 2023 06:09:04 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:42958 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229559AbjHFKJA (ORCPT ); Sun, 6 Aug 2023 06:09:00 -0400 Received: from relay3-d.mail.gandi.net (relay3-d.mail.gandi.net [217.70.183.195]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 2517A131; Sun, 6 Aug 2023 03:08:58 -0700 (PDT) Received: by mail.gandi.net (Postfix) with ESMTPSA id 4585960004; Sun, 6 Aug 2023 10:08:53 +0000 (UTC) Message-ID: Date: Sun, 6 Aug 2023 12:08:52 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.13.0 Subject: Re: [PATCH v8 4/4] RISC-V: mm: Document mmap changes Content-Language: en-US To: Charlie Jenkins , linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org Cc: 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 References: <20230727212647.4182407-1-charlie@rivosinc.com> <20230727212647.4182407-5-charlie@rivosinc.com> From: Alexandre Ghiti In-Reply-To: <20230727212647.4182407-5-charlie@rivosinc.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-GND-Sasl: alex@ghiti.fr Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 27/07/2023 23:26, Charlie Jenkins wrote: > 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. You can add: Reviewed-by: Alexandre Ghiti Thanks, Alex