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 bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (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 93BF0FF8873 for ; Thu, 30 Apr 2026 13:29:56 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:Content-Transfer-Encoding: Content-Type:MIME-Version:References:In-Reply-To:Message-ID:Date:Subject:Cc: To:From:Reply-To:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=YuKxCgQE56OushmPFY2l3FfpElwNcEiVBY235DtF8z8=; b=dpNMtj68PzUEA4f9iqipVa4oDq 7pZe1Wd37shuyGVWFf+Y8xcM0jrgPP0DE86mchnnnKVpeUWCG6QEYKb8Xc/3ssJYXFCTlg6hWuXB1 bQqAIy/E6FGpnLIKbdBNsthgVyeTC/xw+iRl3TUa+xO25oIr+odZHB3/pfqxRbzEY1AIoDe68v2kP V8II/EQNbeitfiDXUdR+XryeegQqWUL2eAxekJ6ySL7jChE4APpM6aeFv4pPQXqfZtydvL1eeS5Ik gLq2Sdgoz3CinbhEwfpNsbb856eIUZu7YNVaikNejRLEOTlXAdYRL/jeWqmT4A0pBLhUqMZWHVIEG O0u2Ip6Q==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98.2 #2 (Red Hat Linux)) id 1wIRSi-00000005XTC-1EZf; Thu, 30 Apr 2026 13:29:52 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.98.2 #2 (Red Hat Linux)) id 1wIRSf-00000005XSG-3hJE for linux-arm-kernel@lists.infradead.org; Thu, 30 Apr 2026 13:29:51 +0000 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id EBE341AED; Thu, 30 Apr 2026 06:29:42 -0700 (PDT) Received: from devkitleo.cambridge.arm.com (devkitleo.cambridge.arm.com [10.1.196.90]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id D026C3F7B4; Thu, 30 Apr 2026 06:29:42 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=arm.com; s=foss; t=1777555788; bh=/W1GRuxZq0cC6A7wpquemE4YB2GQRO11YgKNzJgpAzE=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=MIV0wfnWvMpN+DWDEs3DC7LO+ywU67ncAAqeBECPc/hmIVJgitsfq1OPtKUbFTwdg nvOWGEn5C1XToufUlAVzncZQtaq2SSb2kSiSyexB5Rb+sxsNKCvPTOvEJa/YsvsNmT E6Ci7q2Kk9ABl0De8i+eB010YSc/82PNfDsg8rYA= From: Leonardo Bras To: Marc Zyngier Cc: Leonardo Bras , Catalin Marinas , Will Deacon , Oliver Upton , Joey Gouly , Suzuki K Poulose , Zenghui Yu , "Rafael J. Wysocki" , Len Brown , Saket Dumbre , Paolo Bonzini , Chengwen Feng , Jonathan Cameron , Kees Cook , =?utf-8?Q?Miko=C5=82aj?= Lenczewski , Ryan Roberts , Yang Shi , Thomas Huth , mrigendrachaubey , Yeoreum Yun , Mark Brown , Kevin Brodsky , James Clark , Ard Biesheuvel , Fuad Tabba , Raghavendra Rao Ananta , Nathan Chancellor , Vincent Donnefort , Lorenzo Pieralisi , Sascha Bischoff , Anshuman Khandual , Tian Zheng , Wei-Lin Chang , linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev, linux-acpi@vger.kernel.org, acpica-devel@lists.linux.dev, kvm@vger.kernel.org Subject: Re: [PATCH v1 00/12] KVM Dirty-bit cleaning accelerator (HACDBS) Date: Thu, 30 Apr 2026 14:29:37 +0100 Message-ID: X-Mailer: git-send-email 2.54.0 In-Reply-To: <86bjf0zj2p.wl-maz@kernel.org> References: <20260430111424.3479613-2-leo.bras@arm.com> <86bjf0zj2p.wl-maz@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: 8bit X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260430_062950_212978_0E87352F X-CRM114-Status: GOOD ( 32.13 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Thu, Apr 30, 2026 at 02:14:22PM +0100, Marc Zyngier wrote: > On Thu, 30 Apr 2026 12:14:04 +0100, > Leonardo Bras wrote: > > [...] > > I haven't had a chance to look at any of this yet, but just on these > points: > > > b - checkpatch.pl keeps bothering me to add an entry in MAINTAINERS file, > > and I like the idea of maintaining this. Is there any rule or > > common sense on this? Should I add this entry, or should I leave it > > in the arch/arm64/kvm/ general rule? > > No specific entry in MAINTAINERS required (or wanted). This falls into > the normal KVM/arm64 maintenance. And don't worry, we know where to > find you when it will come to fixing this stuff. > Got it > > c - There are some trace_prink() I have left in the code, as they could > > be helpful to check when HACDBS is not performing as well as it > > should. Should I introduce a tracepoint instead? or just ignore it? > > (it's triggered on HACDBS error, but as it falls back to software in > > that case, it should not impact correctness, only performance). > > Debug infrastructure should be preferably *removed* altogether. > trace_printk() is definitely a big no-no. > Will remove it then > > d - In __kvm_arch_dirty_log_clear() there is no way to predict how long > > should be the buffer, so I used 1x PAGE_SIZE, and when it gets full > > it's cleaned and reused. Should I let users configure that over a > > parameter, or is it overthinking? > > How long is a piece of string? We can't know that. A single page feels > very small in the 4kB case, and letting userspace define the size of > that buffer seems a likely requirement. > Ok, as a KVM parameter, or as a compile-time option? > > > > Kernel v7.0.0 + this patchset builds properly, passing both kvm selftests > > for dirty-bit tracking[2], on HW HACDBS enabled or disabled. > > I have absolutely no trust in these tests. > > Have you enabled a VMM to make use of these APIs, and actively > migrated running guests? That's the level of testing I'd like to see, > as the selftests are not what people run in production... > There is no enablement needed on VMM side. Yes, I have created a VM on upstream qemu with --enable-kvm and migrated it on the same host. (Inside a model) That was the first test I used, but then I found out that kvm selftests stress up multiple scenarios in an easier way. Do you prefer me to test on any specific scenario, or does whatever qemu uses as a default parameter work well enough? Thanks! Leo