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 lists.ozlabs.org (lists.ozlabs.org [112.213.38.117]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 04DCFCE7B02 for ; Fri, 6 Sep 2024 11:44:02 +0000 (UTC) Received: from boromir.ozlabs.org (localhost [127.0.0.1]) by lists.ozlabs.org (Postfix) with ESMTP id 4X0ZBT3130z2xBk; Fri, 6 Sep 2024 21:44:01 +1000 (AEST) Authentication-Results: lists.ozlabs.org; arc=none smtp.remote-ip=147.75.193.91 ARC-Seal: i=1; a=rsa-sha256; d=lists.ozlabs.org; s=201707; t=1725623041; cv=none; b=fgmBOTSFiyo2x9jyoe2mSUd3Uc9oLOPcWr89m9x8VjGEqD5KwP4NLM/mtmh/o2F0Gxu7wANarvKdUWSb5hxMBFiMAaIB/g4B3JGK0RKVcjzYiCAmWfTjU/aMFQOgpBnVU+6rysmf3P0ZsH6bRq4b5YdnZ68YnnHDdgbLHpB3895hpNPrKhjbxbeuuTqaO7twbpsspk8Va5axyBRZva/399CmjpAU2t9tDRUx+/Wqw2Wa6ruIHTxJTKfPuojJvHLZL0fkLfT+TFDF8/euoX4mvo1f/no5uaKtvt38X279+qXdiyBu7iL/O8zppHc9A0ML0zGlF02PH+MCq37GBKzVuA== ARC-Message-Signature: i=1; a=rsa-sha256; d=lists.ozlabs.org; s=201707; t=1725623041; c=relaxed/relaxed; bh=jlW+lt5ymLFjFq1OwMUOAB40jG76BrJeobGs1x3SCuw=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=R9MdGY5P38fIt/cJ4RRQpemwo78VvKzFCxp8DZnU52tRelj6B7ccONKcXV92y9saLZppFjkMDJMPRoaTNpJpBXcsV8aCESfOFODrfOhdsXyVKdYIb30Hkgj2GFhd5ewM/cdCMtHp+66fFvZXWIztf35ixXTEAxiTcgjV8nMACVFIN8GoYd7mAF3jG0pCEg/iRmlN35jbPQdQqp0AW0gVdhLnjNDK5x/hQktcVu3D00iDVzRHFnN6nlCqM5nKQAvYiWaRsSXGAHkJYYd4Gpl6ZU3XM6gvbItBF5EyFOH73jqNPk9OO1EbINmvaD5ObJ0p2AL4pp1BJK0p5vIDNX37GQ== ARC-Authentication-Results: i=1; lists.ozlabs.org; dmarc=fail (p=none dis=none) header.from=arm.com; spf=pass (client-ip=147.75.193.91; helo=nyc.source.kernel.org; envelope-from=cmarinas@kernel.org; receiver=lists.ozlabs.org) smtp.mailfrom=kernel.org Authentication-Results: lists.ozlabs.org; dmarc=fail (p=none dis=none) header.from=arm.com Authentication-Results: lists.ozlabs.org; spf=pass (sender SPF authorized) smtp.mailfrom=kernel.org (client-ip=147.75.193.91; helo=nyc.source.kernel.org; envelope-from=cmarinas@kernel.org; receiver=lists.ozlabs.org) Received: from nyc.source.kernel.org (nyc.source.kernel.org [147.75.193.91]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 4X0ZBS35MFz3064 for ; Fri, 6 Sep 2024 21:44:00 +1000 (AEST) Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by nyc.source.kernel.org (Postfix) with ESMTP id 40C6FA44F2B; Fri, 6 Sep 2024 11:43:49 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id AFE75C4CEC4; Fri, 6 Sep 2024 11:43:46 +0000 (UTC) Date: Fri, 6 Sep 2024 12:43:44 +0100 From: Catalin Marinas To: Arnd Bergmann Cc: guoren , Charlie Jenkins , Richard Henderson , Ivan Kokshaysky , Matt Turner , Vineet Gupta , Russell King , Huacai Chen , WANG Xuerui , Thomas Bogendoerfer , "James E . J . Bottomley" , Helge Deller , Michael Ellerman , Nicholas Piggin , Christophe Leroy , Naveen N Rao , Alexander Gordeev , Gerald Schaefer , Heiko Carstens , Vasily Gorbik , Christian Borntraeger , Sven Schnelle , Yoshinori Sato , Rich Felker , John Paul Adrian Glaubitz , "David S . Miller" , Andreas Larsson , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, "H. Peter Anvin" , Andy Lutomirski , Peter Zijlstra , Muchun Song , Andrew Morton , "Liam R. Howlett" , Vlastimil Babka , Lorenzo Stoakes , shuah , Christoph Hellwig , Michal Hocko , "Kirill A. Shutemov" , Chris Torek , Linux-Arch , linux-kernel@vger.kernel.org, linux-alpha@vger.kernel.org, linux-snps-arc@lists.infradead.org, linux-arm-kernel@lists.infradead.org, "linux-csky@vger.kernel.org" , loongarch@lists.linux.dev, linux-mips@vger.kernel.org, linux-parisc@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-s390@vger.kernel.org, linux-sh@vger.kernel.org, sparclinux@vger.kernel.org, linux-mm@kvack.org, linux-kselftest@vger.kernel.org, linux-abi-devel@lists.sourceforge.net Subject: Re: [PATCH RFC v3 1/2] mm: Add personality flag to limit address to 47 bits Message-ID: References: <20240905-patches-below_hint_mmap-v3-0-3cd5564efbbb@rivosinc.com> <20240905-patches-below_hint_mmap-v3-1-3cd5564efbbb@rivosinc.com> <9fc4746b-8e9d-4a75-b966-e0906187e6b7@app.fastmail.com> X-Mailing-List: linuxppc-dev@lists.ozlabs.org List-Id: List-Help: List-Post: List-Subscribe: , , List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: On Fri, Sep 06, 2024 at 09:55:42AM +0000, Arnd Bergmann wrote: > On Fri, Sep 6, 2024, at 09:14, Guo Ren wrote: > > On Fri, Sep 6, 2024 at 3:18 PM Arnd Bergmann wrote: > >> It's also unclear to me how we want this flag to interact with > >> the existing logic in arch_get_mmap_end(), which attempts to > >> limit the default mapping to a 47-bit address space already. > > > > To optimize RISC-V progress, I recommend: > > > > Step 1: Approve the patch. > > Step 2: Update Go and OpenJDK's RISC-V backend to utilize it. > > Step 3: Wait approximately several iterations for Go & OpenJDK > > Step 4: Remove the 47-bit constraint in arch_get_mmap_end() > > I really want to first see a plausible explanation about why > RISC-V can't just implement this using a 47-bit DEFAULT_MAP_WINDOW > like all the other major architectures (x86, arm64, powerpc64), FWIW arm64 actually limits DEFAULT_MAP_WINDOW to 48-bit in the default configuration. We end up with a 47-bit with 16K pages but for a different reason that has to do with LPA2 support (I doubt we need this for the user mapping but we need to untangle some of the macros there; that's for a separate discussion). That said, we haven't encountered any user space problems with a 48-bit DEFAULT_MAP_WINDOW. So I also think RISC-V should follow a similar approach (47 or 48 bit default limit). Better to have some ABI consistency between architectures. One can still ask for addresses above this default limit via mmap(). -- Catalin