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 D980FC3DA4A for ; Thu, 8 Aug 2024 09:55:50 +0000 (UTC) Received: from boromir.ozlabs.org (localhost [IPv6:::1]) by lists.ozlabs.org (Postfix) with ESMTP id 4Wfj914KQWz3026 for ; Thu, 8 Aug 2024 19:55:49 +1000 (AEST) Authentication-Results: lists.ozlabs.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: lists.ozlabs.org; spf=pass (sender SPF authorized) smtp.mailfrom=arm.com (client-ip=217.140.110.172; helo=foss.arm.com; envelope-from=steven.price@arm.com; receiver=lists.ozlabs.org) Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by lists.ozlabs.org (Postfix) with ESMTP id 4Wfj8B52XKz2xjY for ; Thu, 8 Aug 2024 19:55:06 +1000 (AEST) 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 AA0441042; Thu, 8 Aug 2024 02:55:01 -0700 (PDT) Received: from [10.1.26.21] (e122027.cambridge.arm.com [10.1.26.21]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id A95173F6A8; Thu, 8 Aug 2024 02:54:29 -0700 (PDT) Message-ID: Date: Thu, 8 Aug 2024 10:54:24 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v12 02/84] KVM: arm64: Disallow copying MTE to guest memory while KVM is dirty logging To: Catalin Marinas , Sean Christopherson References: <20240726235234.228822-1-seanjc@google.com> <20240726235234.228822-3-seanjc@google.com> From: Steven Price Content-Language: en-GB In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit 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: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, David Matlack , linux-riscv@lists.infradead.org, Claudio Imbrenda , Janosch Frank , Marc Zyngier , Huacai Chen , Christian Borntraeger , Albert Ou , Bibo Mao , loongarch@lists.linux.dev, Paul Walmsley , kvmarm@lists.linux.dev, linux-arm-kernel@lists.infradead.org, linux-mips@vger.kernel.org, Oliver Upton , Palmer Dabbelt , David Stevens , kvm-riscv@lists.infradead.org, Anup Patel , Paolo Bonzini , Tianrui Zhao , linuxppc-dev@lists.ozlabs.org Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On 07/08/2024 17:21, Catalin Marinas wrote: > On Fri, Jul 26, 2024 at 04:51:11PM -0700, Sean Christopherson wrote: >> Disallow copying MTE tags to guest memory while KVM is dirty logging, as >> writing guest memory without marking the gfn as dirty in the memslot could >> result in userspace failing to migrate the updated page. Ideally (maybe?), >> KVM would simply mark the gfn as dirty, but there is no vCPU to work with, >> and presumably the only use case for copy MTE tags _to_ the guest is when >> restoring state on the target. >> >> Fixes: f0376edb1ddc ("KVM: arm64: Add ioctl to fetch/store tags in a guest") >> Signed-off-by: Sean Christopherson >> --- >> arch/arm64/kvm/guest.c | 5 +++++ >> 1 file changed, 5 insertions(+) >> >> diff --git a/arch/arm64/kvm/guest.c b/arch/arm64/kvm/guest.c >> index e1f0ff08836a..962f985977c2 100644 >> --- a/arch/arm64/kvm/guest.c >> +++ b/arch/arm64/kvm/guest.c >> @@ -1045,6 +1045,11 @@ int kvm_vm_ioctl_mte_copy_tags(struct kvm *kvm, >> >> mutex_lock(&kvm->slots_lock); >> >> + if (write && atomic_read(&kvm->nr_memslots_dirty_logging)) { >> + ret = -EBUSY; >> + goto out; >> + } > > There are ways to actually log the page dirtying but I don't think > it's worth it. AFAICT, reading the tags still works and that's what's > used during migration (on the VM where dirty tracking takes place). > > Reviewed-by: Catalin Marinas > Looks sensible to me - my initial thought was "why would a VMM do that?". But it would make sense to actually return a failure rather than letting the VMM shoot itself in the foot. If there's actually a use-case then we could look at making the dirty tracking work, but I'm not convinced there is a good reason. Reviewed-by: Steven Price Thanks, Steve