From: Marc Zyngier <maz@kernel.org>
To: Steven Price <steven.price@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>,
Will Deacon <will@kernel.org>, James Morse <james.morse@arm.com>,
Julien Thierry <julien.thierry.kdev@gmail.com>,
Suzuki K Poulose <suzuki.poulose@arm.com>,
kvmarm@lists.cs.columbia.edu,
linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org, Dave Martin <Dave.Martin@arm.com>,
Mark Rutland <mark.rutland@arm.com>,
Thomas Gleixner <tglx@linutronix.de>,
qemu-devel@nongnu.org, Juan Quintela <quintela@redhat.com>,
"Dr. David Alan Gilbert" <dgilbert@redhat.com>,
Richard Henderson <richard.henderson@linaro.org>,
Peter Maydell <peter.maydell@linaro.org>,
Haibo Xu <Haibo.Xu@arm.com>, Andrew Jones <drjones@redhat.com>
Subject: Re: [PATCH v12 8/8] KVM: arm64: Document MTE capability and ioctl
Date: Thu, 20 May 2021 11:24:11 +0100 [thread overview]
Message-ID: <871ra1vh2s.wl-maz@kernel.org> (raw)
In-Reply-To: <3b4cca00-e81d-322e-6f65-4d0850aac5a5@arm.com>
On Wed, 19 May 2021 15:09:23 +0100,
Steven Price <steven.price@arm.com> wrote:
>
> On 17/05/2021 19:09, Marc Zyngier wrote:
> > On Mon, 17 May 2021 13:32:39 +0100,
> > Steven Price <steven.price@arm.com> 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 <steven.price@arm.com>
> >> ---
> >> 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.
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next prev parent reply other threads:[~2021-05-20 10:25 UTC|newest]
Thread overview: 49+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-17 12:32 [PATCH v12 0/8] MTE support for KVM guest Steven Price
2021-05-17 12:32 ` [PATCH v12 1/8] arm64: mte: Handle race when synchronising tags Steven Price
2021-05-17 14:03 ` Marc Zyngier
2021-05-17 14:56 ` Steven Price
2021-05-19 17:32 ` Catalin Marinas
2021-05-17 12:32 ` [PATCH v12 2/8] arm64: Handle MTE tags zeroing in __alloc_zeroed_user_highpage() Steven Price
2021-05-17 12:32 ` [PATCH v12 3/8] arm64: mte: Sync tags for pages where PTE is untagged Steven Price
2021-05-17 16:14 ` Marc Zyngier
2021-05-19 9:32 ` Steven Price
2021-05-19 17:48 ` Catalin Marinas
2021-05-19 18:06 ` Catalin Marinas
2021-05-20 11:55 ` Steven Price
2021-05-20 12:25 ` Catalin Marinas
2021-05-20 13:02 ` Catalin Marinas
2021-05-20 13:03 ` Steven Price
2021-05-17 12:32 ` [PATCH v12 4/8] arm64: kvm: Introduce MTE VM feature Steven Price
2021-05-17 16:45 ` Marc Zyngier
2021-05-19 10:48 ` Steven Price
2021-05-20 8:51 ` Marc Zyngier
2021-05-20 14:46 ` Steven Price
2021-05-20 11:54 ` Catalin Marinas
2021-05-20 15:05 ` Steven Price
2021-05-20 17:50 ` Catalin Marinas
2021-05-21 9:28 ` Steven Price
2021-05-17 12:32 ` [PATCH v12 5/8] arm64: kvm: Save/restore MTE registers Steven Price
2021-05-17 17:17 ` Marc Zyngier
2021-05-19 13:04 ` Steven Price
2021-05-20 9:46 ` Marc Zyngier
2021-05-20 15:21 ` Steven Price
2021-05-17 12:32 ` [PATCH v12 6/8] arm64: kvm: Expose KVM_ARM_CAP_MTE Steven Price
2021-05-17 17:40 ` Marc Zyngier
2021-05-19 13:26 ` Steven Price
2021-05-20 10:09 ` Marc Zyngier
2021-05-20 10:51 ` Steven Price
2021-05-17 12:32 ` [PATCH v12 7/8] KVM: arm64: ioctl to fetch/store tags in a guest Steven Price
2021-05-17 18:04 ` Marc Zyngier
2021-05-19 13:51 ` Steven Price
2021-05-20 12:05 ` Catalin Marinas
2021-05-20 15:58 ` Steven Price
2021-05-20 17:27 ` Catalin Marinas
2021-05-21 9:42 ` Steven Price
2021-05-24 18:11 ` Catalin Marinas
2021-05-27 7:50 ` Steven Price
2021-05-27 13:08 ` Catalin Marinas
2021-05-17 12:32 ` [PATCH v12 8/8] KVM: arm64: Document MTE capability and ioctl Steven Price
2021-05-17 18:09 ` Marc Zyngier
2021-05-19 14:09 ` Steven Price
2021-05-20 10:24 ` Marc Zyngier [this message]
2021-05-20 10:52 ` Steven Price
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