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=-3.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT 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 54CDCC433DF for ; Wed, 17 Jun 2020 12:39:25 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 3819B20CC7 for ; Wed, 17 Jun 2020 12:39:25 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726688AbgFQMjY (ORCPT ); Wed, 17 Jun 2020 08:39:24 -0400 Received: from foss.arm.com ([217.140.110.172]:57150 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725860AbgFQMjX (ORCPT ); Wed, 17 Jun 2020 08:39:23 -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 CA0781045; Wed, 17 Jun 2020 05:39:20 -0700 (PDT) Received: from e112269-lin.arm.com (unknown [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 078483F71F; Wed, 17 Jun 2020 05:39:18 -0700 (PDT) From: Steven Price To: Catalin Marinas , Marc Zyngier , Will Deacon Cc: Steven Price , James Morse , Julien Thierry , Suzuki K Poulose , kvmarm@lists.cs.columbia.edu, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, Dave Martin , Mark Rutland , Thomas Gleixner Subject: [RFC PATCH 0/2] MTE support for KVM guest Date: Wed, 17 Jun 2020 13:38:42 +0100 Message-Id: <20200617123844.29960-1-steven.price@arm.com> X-Mailer: git-send-email 2.20.1 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org These patches add support to KVM to enable MTE within a guest. It is based on Catalin's v4 MTE user space series[1]. [1] http://lkml.kernel.org/r/20200515171612.1020-1-catalin.marinas%40arm.com Posting as an RFC as I'd like feedback on the approach taken. First a little background on how MTE fits within the architecture: The stage 2 page tables have limited scope for controlling the availability of MTE. If a page is mapped as Normal and cached in stage 2 then it's the stage 1 tables that get to choose whether the memory is tagged or not. So the only way of forbidding tags on a page from the hypervisor is to change the cacheability (or make it device memory) which would cause other problems. Note this restriction fits the intention that a system should have all (general purpose) memory supporting tags if it support MTE, so it's not too surprising. However, the upshot of this is that to enable MTE within a guest all pages of memory mapped into the guest as normal cached pages in stage 2 *must* support MTE (i.e. we must ensure the tags are appropriately sanitised and save/restore the tags during swap etc). My current approach is that KVM transparently upgrades any pages provided by the VMM to be tag-enabled when they are faulted in (i.e. sets the PG_mte_tagged flag on the page) which has the benefit of requiring fewer changes in the VMM. However, save/restore of the VM state still requires the VMM to have a PROT_MTE enabled mapping so that it can access the tag values. A VMM which 'forgets' to enable PROT_MTE would lose the tag values when saving/restoring (tags are RAZ/WI when PROT_MTE isn't set). An alternative approach would be to enforce the VMM provides PROT_MTE memory in the first place. This seems appealing to prevent the above potentially unexpected gotchas with save/restore, however this would also extend to memory that you might not expect to have PROT_MTE (e.g. a shared frame buffer for an emulated graphics card). Comments on the approach (or ideas for alternative approaches) are very welcome. 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 | 9 ++++++++- arch/arm64/include/uapi/asm/kvm.h | 1 + arch/arm64/kvm/hyp/sysreg-sr.c | 12 ++++++++++++ arch/arm64/kvm/reset.c | 8 ++++++++ arch/arm64/kvm/sys_regs.c | 8 ++++++++ virt/kvm/arm/mmu.c | 11 +++++++++++ 7 files changed, 51 insertions(+), 1 deletion(-) -- 2.20.1