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 X-Spam-Level: X-Spam-Status: No, score=-5.5 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 00195C4363C for ; Fri, 2 Oct 2020 15:38:33 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id BAC472074B for ; Fri, 2 Oct 2020 15:38:33 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2388040AbgJBPia (ORCPT ); Fri, 2 Oct 2020 11:38:30 -0400 Received: from foss.arm.com ([217.140.110.172]:39382 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2387938AbgJBPiU (ORCPT ); Fri, 2 Oct 2020 11:38:20 -0400 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 1C8A51396; Fri, 2 Oct 2020 08:38:20 -0700 (PDT) Received: from [192.168.1.179] (unknown [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 1EB183F73B; Fri, 2 Oct 2020 08:38:16 -0700 (PDT) Subject: Re: [PATCH v3 0/2] MTE support for KVM guest To: Andrew Jones Cc: Catalin Marinas , Marc Zyngier , Will Deacon , Mark Rutland , Peter Maydell , "Dr. David Alan Gilbert" , Haibo Xu , Suzuki K Poulose , qemu-devel@nongnu.org, Dave Martin , Juan Quintela , Richard Henderson , linux-kernel@vger.kernel.org, James Morse , Julien Thierry , Thomas Gleixner , kvmarm@lists.cs.columbia.edu, linux-arm-kernel@lists.infradead.org References: <20200925093607.3051-1-steven.price@arm.com> <20201002143640.uzsz3nhr45payhlb@kamzik.brq.redhat.com> From: Steven Price Message-ID: Date: Fri, 2 Oct 2020 16:38:11 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <20201002143640.uzsz3nhr45payhlb@kamzik.brq.redhat.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-GB Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 02/10/2020 15:36, Andrew Jones wrote: > On Fri, Sep 25, 2020 at 10:36:05AM +0100, Steven Price wrote: >> Version 3 of adding MTE support for KVM guests. See the previous (v2) >> posting for background: >> >> https://lore.kernel.org/r/20200904160018.29481-1-steven.price%40arm.com >> >> These patches add support to KVM to enable MTE within a guest. They are >> based on Catalin's v9 MTE user-space support series[1] (currently in >> next). >> >> Changes since v2: >> >> * MTE is no longer a VCPU feature, instead it is a VM cap. >> >> * Being a VM cap means easier probing (check for KVM_CAP_ARM_MTE). >> >> * The cap must be set before any VCPUs are created, preventing any >> shenanigans where MTE is enabled for the guest after memory accesses >> have been performed. >> >> [1] https://lore.kernel.org/r/20200904103029.32083-1-catalin.marinas@arm.com >> >> Steven Price (2): >> arm64: kvm: Save/restore MTE registers >> arm64: kvm: Introduce MTE VCPU feature >> >> arch/arm64/include/asm/kvm_emulate.h | 3 +++ >> arch/arm64/include/asm/kvm_host.h | 7 +++++++ >> arch/arm64/include/asm/sysreg.h | 3 ++- >> arch/arm64/kvm/arm.c | 9 +++++++++ >> arch/arm64/kvm/hyp/include/hyp/sysreg-sr.h | 14 ++++++++++++++ >> arch/arm64/kvm/mmu.c | 15 +++++++++++++++ >> arch/arm64/kvm/sys_regs.c | 20 +++++++++++++++----- >> include/uapi/linux/kvm.h | 1 + >> 8 files changed, 66 insertions(+), 6 deletions(-) >> >> -- >> 2.20.1 >> >> > > Hi Steven, > > These patches look fine to me, but I'd prefer we have a working > implementation in QEMU before we get too excited about the KVM > bits. kvmtool isn't sufficient since it doesn't support migration > (at least afaik). In the past we've implemented features in KVM > that look fine, but then issues have been discovered when trying > to enable them from QEMU, where we also support migration. This > feature looks like there's risk of issues with the userspace side. > Although these two patches would probably stay the same, even if > userspace requires more support. I agree kvmtool isn't a great test because it doesn't support migration. The support in this series is just the basic support for MTE in a guest and we'd need to wait for the QEMU implementation before deciding whether we need any extra support (e.g. kernel interfaces for reading/writing tags as discussed before). However, I don't think there's much danger of the support in this series changing - so extra support can be added when/if it's needed, but I don't think we need to block these series on that - QEMU can just probe for whatever additional support it needs before enabling MTE in a guest. I plan to rebase/repost after -rc1 when the user space support has been merged. Steve