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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 750C0EE499C for ; Wed, 11 Sep 2024 18:21:45 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id D58A5940087; Wed, 11 Sep 2024 14:21:44 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id D0845940066; Wed, 11 Sep 2024 14:21:44 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id B8190940087; Wed, 11 Sep 2024 14:21:44 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0010.hostedemail.com [216.40.44.10]) by kanga.kvack.org (Postfix) with ESMTP id 9A3FF940066 for ; Wed, 11 Sep 2024 14:21:44 -0400 (EDT) Received: from smtpin01.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay09.hostedemail.com (Postfix) with ESMTP id 3B46A80B62 for ; Wed, 11 Sep 2024 18:21:44 +0000 (UTC) X-FDA: 82553275728.01.C321F3C Received: from nyc.source.kernel.org (nyc.source.kernel.org [147.75.193.91]) by imf13.hostedemail.com (Postfix) with ESMTP id A4D5620015 for ; Wed, 11 Sep 2024 18:21:41 +0000 (UTC) Authentication-Results: imf13.hostedemail.com; dkim=none; dmarc=fail reason="SPF not aligned (relaxed), No valid DKIM" header.from=arm.com (policy=none); spf=pass (imf13.hostedemail.com: domain of cmarinas@kernel.org designates 147.75.193.91 as permitted sender) smtp.mailfrom=cmarinas@kernel.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1726078798; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=n6iY5aha6gHF4RHjAIeOymFa2jrsr74IoGTSxFE4JHI=; b=h4funbkCrGRI/Qh0ECdXDItC4nLu0VCjewykixaH0dfmyvslnmCH4NCsUkwvFn6fmHs3ig N2BXw9qcXN+yNrMex4QjmnqYQkpfDjZxO3wJeEt/LO/ecdVJ2A7vfyVCUm59t0sRqezzWC PiJxU/BtXgtphhY5lDJT/6tMtuV4YdU= ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1726078798; a=rsa-sha256; cv=none; b=06MeFGARm4vQoGeU1GILpfV6Milc4/UorT8fD4AIANrAcEGzSKkPa3VUR1SkOCQjfJx47l Sdi8xlORunB0M+Cx9VCMcSmjQKldfYGIxwPk51gaO7Irr53O0GwvWtmEXPu1XW1zKnE9k/ 8iJ9d/sAz7GC2r4icq7Pbqk5xH/Atc0= ARC-Authentication-Results: i=1; imf13.hostedemail.com; dkim=none; dmarc=fail reason="SPF not aligned (relaxed), No valid DKIM" header.from=arm.com (policy=none); spf=pass (imf13.hostedemail.com: domain of cmarinas@kernel.org designates 147.75.193.91 as permitted sender) smtp.mailfrom=cmarinas@kernel.org Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by nyc.source.kernel.org (Postfix) with ESMTP id C7BBCA45341; Wed, 11 Sep 2024 18:21:32 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 3AB7BC4CEC0; Wed, 11 Sep 2024 18:21:30 +0000 (UTC) Date: Wed, 11 Sep 2024 19:21:27 +0100 From: Catalin Marinas To: Charlie Jenkins Cc: "Liam R. Howlett" , Arnd Bergmann , guoren , 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 , 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> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Rspamd-Queue-Id: A4D5620015 X-Stat-Signature: pq6opxz88hacg3813g5usn6ny76adpcu X-Rspamd-Server: rspam09 X-Rspam-User: X-HE-Tag: 1726078901-333955 X-HE-Meta: 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 X7V8978a 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, Sep 10, 2024 at 05:45:07PM -0700, Charlie Jenkins wrote: > On Tue, Sep 10, 2024 at 03:08:14PM -0400, Liam R. Howlett wrote: > > * Catalin Marinas [240906 07:44]: > > > 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() Point 4 is an ABI change. What guarantees that there isn't still software out there that relies on the old behaviour? > > > > 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(). > > > > I think that is best as well. > > > > Can we please just do what x86 and arm64 does? > > I responded to Arnd in the other thread, but I am still not convinced > that the solution that x86 and arm64 have selected is the best solution. > The solution of defaulting to 47 bits does allow applications the > ability to get addresses that are below 47 bits. However, due to > differences across architectures it doesn't seem possible to have all > architectures default to the same value. Additionally, this flag will be > able to help users avoid potential bugs where a hint address is passed > that causes upper bits of a VA to be used. The reason we added this limit on arm64 is that we noticed programs using the top 8 bits of a 64-bit pointer for additional information. IIRC, it wasn't even openJDK but some JavaScript JIT. We could have taught those programs of a new flag but since we couldn't tell how many are out there, it was the safest to default to a smaller limit and opt in to the higher one. Such opt-in is via mmap() but if you prefer a prctl() flag, that's fine by me as well (though I think this should be opt-in to higher addresses rather than opt-out of the higher addresses). -- Catalin