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 4AAF5C7618E for ; Fri, 21 Apr 2023 17:11:38 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233436AbjDURLg (ORCPT ); Fri, 21 Apr 2023 13:11:36 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:55216 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233368AbjDURLb (ORCPT ); Fri, 21 Apr 2023 13:11:31 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 7ECEB16B23; Fri, 21 Apr 2023 10:11:02 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 4BD6061084; Fri, 21 Apr 2023 17:11:01 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id B12ECC433D2; Fri, 21 Apr 2023 17:11:00 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1682097060; bh=DnRJVkdO+iXXcujqYX0KJiluJwWD+2pWlYT4caOjV0E=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=EHqT+C8njFjfHsi70rZiFdTrbu/ie2fbzv5GWFi7pafMAdvhkg+xjmdkME5V+TP5H vcLBHMLLGFbsS6Bh5vypOpKExqOA8wsRzF41qmZ19WzWKshlk3u9i0D0aXorNQzjsL nQpYWA+mm/4JtT8Uwm4DBOpUtNdlt85q/uiLWvjEUOn2ZnHqCgjzx1pGUZyWRwl9U3 I41Jwu+sshMCbAC8Y0Ew+K9z6kUOnYFRIA8TNf11u2KxRLFc8FeFiRoyQxIli0As/N m14zF/WcXp/SNioGllvt5vra6edJysaPm4tYR2VfzMlV49j4IaFjTG0hvQMliIapd3 qihad4ZVYUIAA== Received: from sofa.misterjones.org ([185.219.108.64] helo=goblin-girl.misterjones.org) by disco-boy.misterjones.org with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.95) (envelope-from ) id 1ppuHi-00AFeg-8D; Fri, 21 Apr 2023 18:10:58 +0100 Date: Fri, 21 Apr 2023 18:10:57 +0100 Message-ID: <86pm7xjh3y.wl-maz@kernel.org> From: Marc Zyngier To: Vipin Sharma Cc: oliver.upton@linux.dev, james.morse@arm.com, suzuki.poulose@arm.com, yuzenghui@huawei.com, catalin.marinas@arm.com, will@kernel.org, chenhuacai@kernel.org, aleksandar.qemu.devel@gmail.com, tsbogend@alpha.franken.de, anup@brainfault.org, atishp@atishpatra.org, paul.walmsley@sifive.com, palmer@dabbelt.com, aou@eecs.berkeley.edu, seanjc@google.com, pbonzini@redhat.com, dmatlack@google.com, ricarkol@google.com, linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev, linux-mips@vger.kernel.org, kvm-riscv@lists.infradead.org, linux-riscv@lists.infradead.org, linux-kselftest@vger.kernel.org, kvm@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 9/9] KVM: arm64: Run clear-dirty-log under MMU read lock In-Reply-To: <20230421165305.804301-10-vipinsh@google.com> References: <20230421165305.804301-1-vipinsh@google.com> <20230421165305.804301-10-vipinsh@google.com> User-Agent: Wanderlust/2.15.9 (Almost Unreal) SEMI-EPG/1.14.7 (Harue) FLIM-LB/1.14.9 (=?UTF-8?B?R29qxY0=?=) APEL-LB/10.8 EasyPG/1.0.0 Emacs/28.2 (aarch64-unknown-linux-gnu) MULE/6.0 (HANACHIRUSATO) MIME-Version: 1.0 (generated by SEMI-EPG 1.14.7 - "Harue") Content-Type: text/plain; charset=US-ASCII X-SA-Exim-Connect-IP: 185.219.108.64 X-SA-Exim-Rcpt-To: vipinsh@google.com, oliver.upton@linux.dev, james.morse@arm.com, suzuki.poulose@arm.com, yuzenghui@huawei.com, catalin.marinas@arm.com, will@kernel.org, chenhuacai@kernel.org, aleksandar.qemu.devel@gmail.com, tsbogend@alpha.franken.de, anup@brainfault.org, atishp@atishpatra.org, paul.walmsley@sifive.com, palmer@dabbelt.com, aou@eecs.berkeley.edu, seanjc@google.com, pbonzini@redhat.com, dmatlack@google.com, ricarkol@google.com, linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev, linux-mips@vger.kernel.org, kvm-riscv@lists.infradead.org, linux-riscv@lists.infradead.org, linux-kselftest@vger.kernel.org, kvm@vger.kernel.org, linux-kernel@vger.kernel.org X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on disco-boy.misterjones.org); SAEximRunCond expanded to false Precedence: bulk List-ID: X-Mailing-List: linux-mips@vger.kernel.org On Fri, 21 Apr 2023 17:53:05 +0100, Vipin Sharma wrote: > > Take MMU read lock for write protecting PTEs and use shared page table > walker for clearing dirty logs. > > Clearing dirty logs are currently performed under MMU write locks. This > means vCPUs write protection fault, which also take MMU read lock, will > be blocked during this operation. This causes guest degradation and > especially noticeable on VMs with lot of vCPUs. > > Taking MMU read lock will allow vCPUs to execute parallelly and reduces > the impact on vCPUs performance. Sure. Taking no lock whatsoever would be even better. What I don't see is the detailed explanation that gives me the warm feeling that this is safe and correct. Such an explanation is the minimum condition for me to even read the patch. Thanks, M. -- Without deviation from the norm, progress is not possible.