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 9204CC48BEB for ; Fri, 16 Feb 2024 12:30:54 +0000 (UTC) Received: from boromir.ozlabs.org (localhost [IPv6:::1]) by lists.ozlabs.org (Postfix) with ESMTP id 4TbrrF1r22z3vdl for ; Fri, 16 Feb 2024 23:30:53 +1100 (AEDT) Authentication-Results: lists.ozlabs.org; spf=pass (sender SPF authorized) smtp.mailfrom=kernel.org (client-ip=145.40.73.55; helo=sin.source.kernel.org; envelope-from=cmarinas@kernel.org; receiver=lists.ozlabs.org) Received: from sin.source.kernel.org (sin.source.kernel.org [145.40.73.55]) (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 4Tbrqj4Rz8z3dXP for ; Fri, 16 Feb 2024 23:30:25 +1100 (AEDT) Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by sin.source.kernel.org (Postfix) with ESMTP id 234B6CE293E; Fri, 16 Feb 2024 12:30:20 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id DA0D8C433C7; Fri, 16 Feb 2024 12:30:14 +0000 (UTC) Date: Fri, 16 Feb 2024 12:30:12 +0000 From: Catalin Marinas To: Ryan Roberts Subject: Re: [PATCH v6 13/18] arm64/mm: Implement new wrprotect_ptes() batch API Message-ID: References: <20240215103205.2607016-1-ryan.roberts@arm.com> <20240215103205.2607016-14-ryan.roberts@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20240215103205.2607016-14-ryan.roberts@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 Thu, Feb 15, 2024 at 10:32:00AM +0000, Ryan Roberts wrote: > Optimize the contpte implementation to fix some of the fork performance > regression introduced by the initial contpte commit. Subsequent patches > will solve it entirely. > > During fork(), any private memory in the parent must be write-protected. > Previously this was done 1 PTE at a time. But the core-mm supports > batched wrprotect via the new wrprotect_ptes() API. So let's implement > that API and for fully covered contpte mappings, we no longer need to > unfold the contpte. This has 2 benefits: > > - reduced unfolding, reduces the number of tlbis that must be issued. > - The memory remains contpte-mapped ("folded") in the parent, so it > continues to benefit from the more efficient use of the TLB after > the fork. > > The optimization to wrprotect a whole contpte block without unfolding is > possible thanks to the tightening of the Arm ARM in respect to the > definition and behaviour when 'Misprogramming the Contiguous bit'. See > section D21194 at https://developer.arm.com/documentation/102105/ja-07/ > > Tested-by: John Hubbard > Signed-off-by: Ryan Roberts Acked-by: Catalin Marinas