From patchwork Fri Sep 4 16:00:16 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Steven Price X-Patchwork-Id: 1357729 Return-Path: X-Original-To: incoming@patchwork.ozlabs.org Delivered-To: patchwork-incoming@bilbo.ozlabs.org Authentication-Results: ozlabs.org; spf=pass (sender SPF authorized) smtp.mailfrom=nongnu.org (client-ip=209.51.188.17; helo=lists.gnu.org; envelope-from=qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org; receiver=) Authentication-Results: ozlabs.org; dmarc=none (p=none dis=none) header.from=arm.com Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ozlabs.org (Postfix) with ESMTPS id 4BjjNj5m77z9sVB for ; Sat, 5 Sep 2020 02:11:49 +1000 (AEST) Received: from localhost ([::1]:48530 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1kEEJX-0007oO-En for incoming@patchwork.ozlabs.org; Fri, 04 Sep 2020 12:11:47 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:60112) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1kEE8f-0002cy-Vn for qemu-devel@nongnu.org; Fri, 04 Sep 2020 12:00:35 -0400 Received: from foss.arm.com ([217.140.110.172]:45922) by eggs.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1kEE8c-0001dk-VM for qemu-devel@nongnu.org; Fri, 04 Sep 2020 12:00:33 -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 2935E11B3; Fri, 4 Sep 2020 09:00:27 -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 AD76B3F66F; Fri, 4 Sep 2020 09:00:24 -0700 (PDT) From: Steven Price To: Catalin Marinas , Marc Zyngier , Will Deacon Subject: [PATCH v2 0/2] MTE support for KVM guest Date: Fri, 4 Sep 2020 17:00:16 +0100 Message-Id: <20200904160018.29481-1-steven.price@arm.com> X-Mailer: git-send-email 2.20.1 MIME-Version: 1.0 Received-SPF: pass client-ip=217.140.110.172; envelope-from=steven.price@arm.com; helo=foss.arm.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/09/04 12:00:27 X-ACL-Warn: Detected OS = Linux 3.11 and newer [fuzzy] X-Spam_score_int: -41 X-Spam_score: -4.2 X-Spam_bar: ---- X-Spam_report: (-4.2 / 5.0 requ) BAYES_00=-1.9, RCVD_IN_DNSWL_MED=-2.3, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Mark Rutland , "Dr. David Alan Gilbert" , Peter Maydell , Haibo Xu , Suzuki K Poulose , qemu-devel@nongnu.org, Dave Martin , Juan Quintela , Richard Henderson , linux-kernel@vger.kernel.org, Steven Price , James Morse , Julien Thierry , Thomas Gleixner , kvmarm@lists.cs.columbia.edu, linux-arm-kernel@lists.infradead.org Errors-To: qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org Sender: "Qemu-devel" Arm's Memory Tagging Extension (MTE) adds 4 bits of tag data to every 16 bytes of memory in the system. This along with stashing a tag within the high bit of virtual addresses allows runtime checking of memory accesses. 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]. I'd welcome feedback on the proposed user-kernel ABI. Specifically this series currently: 1. Requires the VMM to enable MTE per-VCPU. 2. Automatically promotes (normal host) memory given to the guest to be tag enabled (sets PG_mte_tagged), if any VCPU has MTE enabled. The tags are cleared if the memory wasn't previously MTE enabled. 3. Doesn't provide any new methods for the VMM to access the tags on memory. (2) and (3) are particularly interesting from the aspect of VM migration. The guest is able to store/retrieve data in the tags (presumably for the purpose of tag checking, but architecturally it could be used as just storage). This means that when migrating a guest the data needs to be transferred (or saved/restored). MTE tags are controlled by the same permission model as normal pages (i.e. a read-only page has read-only tags), so the normal methods of detecting guest changes to pages can be used. But this would also require the tags within a page to be migrated at the same time as the data (since the access control for tags is the same as the normal data within a page). (3) may be problematic and I'd welcome input from those familiar with VMMs. User space cannot access tags unless the memory is mapped with the PROT_MTE flag. However enabling PROT_MTE will also enable tag checking for the user space process (assuming the VMM enables tag checking for the process) and since the tags in memory are controlled by the guest it's unlikely the VMM would have an appropriately tagged pointer for its access. This means the VMM would either need to maintain two mappings of memory (one to access tags, the other to access data) or disable tag checking during the accesses to data. If it's not practical to either disable tag checking in the VMM or maintain multiple mappings then the alternatives I'm aware of are: * Provide a KVM-specific method to extract the tags from guest memory. This might also have benefits in terms of providing an easy way to read bulk tag data from guest memory (since the LDGM instruction isn't available at EL0). * Provide support for user space setting the TCMA0 or TCMA1 bits in TCR_EL1. These would allow the VMM to generate pointers which are not tag checked. Feedback is welcome, and feel free to ask questions if anything in the above doesn't make sense. Changes since the previous v1 posting[2]: * Rebasing clean-ups * sysreg visibility is now controlled based on whether the VCPU has MTE enabled or not [1] https://lore.kernel.org/r/20200904103029.32083-1-catalin.marinas@arm.com [2] https://lore.kernel.org/r/20200713100102.53664-1-steven.price%40arm.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 | 9 ++++++++- arch/arm64/include/asm/sysreg.h | 3 ++- arch/arm64/include/uapi/asm/kvm.h | 1 + arch/arm64/kvm/hyp/include/hyp/sysreg-sr.h | 14 ++++++++++++++ arch/arm64/kvm/mmu.c | 15 +++++++++++++++ arch/arm64/kvm/reset.c | 8 ++++++++ arch/arm64/kvm/sys_regs.c | 20 +++++++++++++++----- 8 files changed, 66 insertions(+), 7 deletions(-)