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 B9616C52D71 for ; Thu, 8 Aug 2024 09:55:53 +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:In-Reply-To:From:References:Cc:To:Subject:MIME-Version:Date: Message-ID:Reply-To:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=SZud+4dwHq1bCnXQRkT5uKWf6J/tpTC1Al143iOa4z0=; b=qXUMQM1lVdE/f80CLATApR24S0 vgy0IUDxJFjoy1tavEOZnzHZcfc+i7yMmkG7poorjQwPDvEsz4JLJA2iINJXFuPg14jPaKRMGg0/b 4PQnZOFsOFBhUFaa8wXZ+Qj0VmSiY4EvHOUgl6W1bACbwxm9bXJpsb3padudw4NjhuPiMzqLxiRCi mrNFWPhWydgekvfM/u+lxIbvxxcvCxcEozBfJcuwmz/mTVcBrAOcCYVfguzhhp7usKVL73EsDnjON 6TjYJ7S1YMP0hytbEUAw96nmBo9kX60OPZTzJ25IE5YM0EhTCxelRD5/ItxrOBOh3dL98JWDT14bO 2Osg2daw==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.97.1 #2 (Red Hat Linux)) id 1sbzrx-00000007nEL-47ke; Thu, 08 Aug 2024 09:55:41 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.97.1 #2 (Red Hat Linux)) id 1sbzqu-00000007mvY-1yAt; Thu, 08 Aug 2024 09:54:37 +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 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 Cc: Paolo Bonzini , Marc Zyngier , Oliver Upton , Tianrui Zhao , Bibo Mao , Huacai Chen , Michael Ellerman , Anup Patel , Paul Walmsley , Palmer Dabbelt , Albert Ou , Christian Borntraeger , Janosch Frank , Claudio Imbrenda , kvm@vger.kernel.org, linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev, loongarch@lists.linux.dev, linux-mips@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, kvm-riscv@lists.infradead.org, linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org, David Matlack , David Stevens 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-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20240808_025436_590233_177625F0 X-CRM114-Status: GOOD ( 17.00 ) 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 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