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 3DCF0C48260 for ; Fri, 16 Feb 2024 16:56:46 +0000 (UTC) Received: from boromir.ozlabs.org (localhost [IPv6:::1]) by lists.ozlabs.org (Postfix) with ESMTP id 4Tbyl14JRzz3vf7 for ; Sat, 17 Feb 2024 03:56:45 +1100 (AEDT) Authentication-Results: lists.ozlabs.org; spf=pass (sender SPF authorized) smtp.mailfrom=kernel.org (client-ip=139.178.84.217; helo=dfw.source.kernel.org; envelope-from=cmarinas@kernel.org; receiver=lists.ozlabs.org) Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) (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 4TbykX4w59z3dSv for ; Sat, 17 Feb 2024 03:56:20 +1100 (AEDT) Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by dfw.source.kernel.org (Postfix) with ESMTP id B4FC861FFE; Fri, 16 Feb 2024 16:56:17 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 7A7B0C433F1; Fri, 16 Feb 2024 16:56:12 +0000 (UTC) Date: Fri, 16 Feb 2024 16:56:10 +0000 From: Catalin Marinas To: Ryan Roberts Subject: Re: [PATCH v6 12/18] arm64/mm: Wire up PTE_CONT for user mappings Message-ID: References: <20240215103205.2607016-1-ryan.roberts@arm.com> <20240215103205.2607016-13-ryan.roberts@arm.com> <892caa6a-e4fe-4009-aa33-0570526961c5@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <892caa6a-e4fe-4009-aa33-0570526961c5@arm.com> X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Mark Rutland , Kefeng Wang , x86@kernel.org, David Hildenbrand , Yang Shi , Dave Hansen , linux-mm@kvack.org, Andrey Ryabinin , "H. Peter Anvin" , Will Deacon , Ard Biesheuvel , Marc Zyngier , Alistair Popple , Barry Song <21cnbao@gmail.com>, Matthew Wilcox , Ingo Molnar , Zi Yan , John Hubbard , Borislav Petkov , Thomas Gleixner , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, James Morse , Andrew Morton , linuxppc-dev@lists.ozlabs.org Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On Fri, Feb 16, 2024 at 12:53:43PM +0000, Ryan Roberts wrote: > On 16/02/2024 12:25, Catalin Marinas wrote: > > On Thu, Feb 15, 2024 at 10:31:59AM +0000, Ryan Roberts wrote: > >> arch/arm64/mm/contpte.c | 285 +++++++++++++++++++++++++++++++ > > > > Nitpick: I think most symbols in contpte.c can be EXPORT_SYMBOL_GPL(). > > We don't expect them to be used by random out of tree modules. In fact, > > do we expect them to end up in modules at all? Most seem to be called > > from the core mm code. > > The problem is that the contpte_* symbols are called from the ptep_* inline > functions. So where those inlines are called from modules, we need to make sure > the contpte_* symbols are available. > > John Hubbard originally reported this problem against v1 and I enumerated all > the drivers that call into the ptep_* inlines here: > https://lore.kernel.org/linux-arm-kernel/b994ff89-1a1f-26ca-9479-b08c77f94be8@arm.com/#t > > So they definitely need to be exported. Perhaps we can tighten it to > EXPORT_SYMBOL_GPL(), but I was being cautious as I didn't want to break anything > out-of-tree. I'm not sure what the normal policy is? arm64 seems to use ~equal > amounts of both. I don't think we are consistent here. For example set_pte_at() can't be called from non-GPL modules because of __sync_icache_dcache. OTOH, such driver is probably doing something dodgy. Same with apply_to_page_range(), it's GPL-only (called from i915). Let's see if others have any view over the next week or so, otherwise I'd go for _GPL and relax it later if someone has a good use-case (can be a patch on top adding _GPL). > > If you can make this easier to parse (in a few years time) with an > > additional patch adding some more comments, that would be great. For > > this patch: > > I already have a big block comment at the top, which was trying to explain it. > Clearly not well enough though. I'll add more comments as a follow up patch when > I get back from holiday. I read that comment but it wasn't immediately obvious what the atomicity requirements are - basically we require a single PTE to be atomically read (which it is), the rest is the dirty/young state being added on top. I guess a sentence along these lines would do. Enjoy your holiday! -- Catalin