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Thu, 20 May 2021 10:24:15 +0000 Received: from disco-boy.misterjones.org (disco-boy.misterjones.org [51.254.78.96]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 142BA61279; Thu, 20 May 2021 10:24:14 +0000 (UTC) Received: from 78.163-31-62.static.virginmediabusiness.co.uk ([62.31.163.78] helo=why.misterjones.org) by disco-boy.misterjones.org with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.94.2) (envelope-from ) id 1ljfqe-002V85-2q; Thu, 20 May 2021 11:24:12 +0100 Date: Thu, 20 May 2021 11:24:11 +0100 Message-ID: <871ra1vh2s.wl-maz@kernel.org> From: Marc Zyngier To: Steven Price 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 Subject: Re: [PATCH v12 8/8] KVM: arm64: Document MTE capability and ioctl In-Reply-To: <3b4cca00-e81d-322e-6f65-4d0850aac5a5@arm.com> References: <20210517123239.8025-1-steven.price@arm.com> <20210517123239.8025-9-steven.price@arm.com> <87r1i5teou.wl-maz@kernel.org> <3b4cca00-e81d-322e-6f65-4d0850aac5a5@arm.com> User-Agent: Wanderlust/2.15.9 (Almost Unreal) SEMI-EPG/1.14.7 (Harue) FLIM-LB/1.14.9 (=?UTF-8?B?R29qxY0=?=) APEL-LB/10.8 EasyPG/1.0.0 Emacs/27.1 (x86_64-pc-linux-gnu) MULE/6.0 (HANACHIRUSATO) MIME-Version: 1.0 (generated by SEMI-EPG 1.14.7 - "Harue") X-SA-Exim-Connect-IP: 62.31.163.78 X-SA-Exim-Rcpt-To: steven.price@arm.com, catalin.marinas@arm.com, will@kernel.org, james.morse@arm.com, julien.thierry.kdev@gmail.com, suzuki.poulose@arm.com, kvmarm@lists.cs.columbia.edu, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, Dave.Martin@arm.com, mark.rutland@arm.com, tglx@linutronix.de, qemu-devel@nongnu.org, quintela@redhat.com, dgilbert@redhat.com, richard.henderson@linaro.org, peter.maydell@linaro.org, Haibo.Xu@arm.com, drjones@redhat.com X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on disco-boy.misterjones.org); SAEximRunCond expanded to false X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20210520_032414_509243_C413ED4E X-CRM114-Status: GOOD ( 42.49 ) 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: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Wed, 19 May 2021 15:09:23 +0100, Steven Price wrote: > > 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. Dropping the mention of this symbol and replacing it by the value 16 matches the architecture and doesn't require any extra UAPI definition, so let's just do that. > > >> +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. I believe the architecture is quite clear that it *is* limited to AArch64. The clarification is welcome though. M. -- Without deviation from the norm, progress is not possible. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel