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=-15.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_SANE_1 autolearn=ham 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 15ADDC43462 for ; Wed, 19 May 2021 14:09:42 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id E79F46135A for ; Wed, 19 May 2021 14:09:41 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1347103AbhESOLA (ORCPT ); Wed, 19 May 2021 10:11:00 -0400 Received: from foss.arm.com ([217.140.110.172]:41372 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1347040AbhESOK5 (ORCPT ); Wed, 19 May 2021 10:10:57 -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 D3F6431B; Wed, 19 May 2021 07:09:37 -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 5F3503F73B; Wed, 19 May 2021 07:09:35 -0700 (PDT) Subject: Re: [PATCH v12 8/8] KVM: arm64: Document MTE capability and ioctl To: Marc Zyngier Cc: Catalin Marinas , Will Deacon , 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 , qemu-devel@nongnu.org, Juan Quintela , "Dr. David Alan Gilbert" , Richard Henderson , Peter Maydell , Haibo Xu , Andrew Jones References: <20210517123239.8025-1-steven.price@arm.com> <20210517123239.8025-9-steven.price@arm.com> <87r1i5teou.wl-maz@kernel.org> From: Steven Price Message-ID: <3b4cca00-e81d-322e-6f65-4d0850aac5a5@arm.com> Date: Wed, 19 May 2021 15:09:23 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.8.1 MIME-Version: 1.0 In-Reply-To: <87r1i5teou.wl-maz@kernel.org> Content-Type: text/plain; charset=utf-8 Content-Language: en-GB Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 17/05/2021 19:09, Marc Zyngier wrote: > On Mon, 17 May 2021 13:32:39 +0100, > Steven Price wrote: >> >> A new capability (KVM_CAP_ARM_MTE) identifies that the kernel supports >> granting a guest access to the tags, and provides a mechanism for the >> VMM to enable it. >> >> A new ioctl (KVM_ARM_MTE_COPY_TAGS) provides a simple way for a VMM to >> access the tags of a guest without having to maintain a PROT_MTE mapping >> in userspace. The above capability gates access to the ioctl. >> >> Signed-off-by: Steven Price >> --- >> Documentation/virt/kvm/api.rst | 53 ++++++++++++++++++++++++++++++++++ >> 1 file changed, 53 insertions(+) >> >> diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst >> index 22d077562149..a31661b870ba 100644 >> --- a/Documentation/virt/kvm/api.rst >> +++ b/Documentation/virt/kvm/api.rst >> @@ -5034,6 +5034,40 @@ see KVM_XEN_VCPU_SET_ATTR above. >> The KVM_XEN_VCPU_ATTR_TYPE_RUNSTATE_ADJUST type may not be used >> with the KVM_XEN_VCPU_GET_ATTR ioctl. >> >> +4.130 KVM_ARM_MTE_COPY_TAGS >> +--------------------------- >> + >> +:Capability: KVM_CAP_ARM_MTE >> +:Architectures: arm64 >> +:Type: vm ioctl >> +:Parameters: struct kvm_arm_copy_mte_tags >> +:Returns: 0 on success, < 0 on error >> + >> +:: >> + >> + struct kvm_arm_copy_mte_tags { >> + __u64 guest_ipa; >> + __u64 length; >> + union { >> + void __user *addr; >> + __u64 padding; >> + }; >> + __u64 flags; >> + __u64 reserved[2]; >> + }; > > This doesn't exactly match the structure in the previous patch :-(. :( I knew there was a reason I didn't include it in the documentation for the first 9 versions... I'll fix this up, thanks for spotting it. >> + >> +Copies Memory Tagging Extension (MTE) tags to/from guest tag memory. The >> +``guest_ipa`` and ``length`` fields must be ``PAGE_SIZE`` aligned. The ``addr`` >> +fieldmust point to a buffer which the tags will be copied to or from. >> + >> +``flags`` specifies the direction of copy, either ``KVM_ARM_TAGS_TO_GUEST`` or >> +``KVM_ARM_TAGS_FROM_GUEST``. >> + >> +The size of the buffer to store the tags is ``(length / MTE_GRANULE_SIZE)`` > > Should we add a UAPI definition for MTE_GRANULE_SIZE? I wasn't sure whether to export this or not. The ioctl is based around the existing ptrace interface (PTRACE_{PEEK,POKE}MTETAGS) which doesn't expose a UAPI definition. Admittedly the documentation there also just says "16-byte granule" rather than MTE_GRANULE_SIZE. So I'll just remove the reference to MTE_GRANULE_SIZE in the documentation unless you feel that we should have a UAPI definition. >> +bytes (i.e. 1/16th of the corresponding size). Each byte contains a single tag >> +value. This matches the format of ``PTRACE_PEEKMTETAGS`` and >> +``PTRACE_POKEMTETAGS``. >> + >> 5. The kvm_run structure >> ======================== >> >> @@ -6362,6 +6396,25 @@ default. >> >> See Documentation/x86/sgx/2.Kernel-internals.rst for more details. >> >> +7.26 KVM_CAP_ARM_MTE >> +-------------------- >> + >> +:Architectures: arm64 >> +:Parameters: none >> + >> +This capability indicates that KVM (and the hardware) supports exposing the >> +Memory Tagging Extensions (MTE) to the guest. It must also be enabled by the >> +VMM before the guest will be granted access. >> + >> +When enabled the guest is able to access tags associated with any memory given >> +to the guest. KVM will ensure that the pages are flagged ``PG_mte_tagged`` so >> +that the tags are maintained during swap or hibernation of the host; however >> +the VMM needs to manually save/restore the tags as appropriate if the VM is >> +migrated. >> + >> +When enabled the VMM may make use of the ``KVM_ARM_MTE_COPY_TAGS`` ioctl to >> +perform a bulk copy of tags to/from the guest. >> + > > Missing limitation to AArch64 guests. As mentioned previously it's not technically limited to AArch64, but I'll expand this to make it clear that MTE isn't usable from a AArch32 VCPU. Thanks, Steve