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Re: [PATCH v4 1/2] arm/kvm: add support for MTE
From: |
Cornelia Huck |
Subject: |
Re: [PATCH v4 1/2] arm/kvm: add support for MTE |
Date: |
Tue, 17 Jan 2023 17:52:06 +0100 |
User-agent: |
Notmuch/0.37 (https://notmuchmail.org) |
On Tue, Jan 17 2023, Peter Maydell <peter.maydell@linaro.org> wrote:
> On Wed, 11 Jan 2023 at 16:13, Cornelia Huck <cohuck@redhat.com> wrote:
>>
>> Introduce a new cpu feature flag to control MTE support. To preserve
>> backwards compatibility for tcg, MTE will continue to be enabled as
>> long as tag memory has been provided.
>>
>> If MTE has been enabled, we need to disable migration, as we do not
>> yet have a way to migrate the tags as well. Therefore, MTE will stay
>> off with KVM unless requested explicitly.
>>
>> Signed-off-by: Cornelia Huck <cohuck@redhat.com>
>> ---
>> docs/system/arm/cpu-features.rst | 21 +++++
>> hw/arm/virt.c | 2 +-
>> target/arm/cpu.c | 18 ++---
>> target/arm/cpu.h | 1 +
>> target/arm/cpu64.c | 133 +++++++++++++++++++++++++++++++
>> target/arm/internals.h | 1 +
>> target/arm/kvm64.c | 5 ++
>> target/arm/kvm_arm.h | 12 +++
>> target/arm/monitor.c | 1 +
>> 9 files changed, 181 insertions(+), 13 deletions(-)
>>
>> diff --git a/docs/system/arm/cpu-features.rst
>> b/docs/system/arm/cpu-features.rst
>> index 00c444042ff5..e278650c837e 100644
>> --- a/docs/system/arm/cpu-features.rst
>> +++ b/docs/system/arm/cpu-features.rst
>> @@ -443,3 +443,24 @@ As with ``sve-default-vector-length``, if the default
>> length is larger
>> than the maximum vector length enabled, the actual vector length will
>> be reduced. If this property is set to ``-1`` then the default vector
>> length is set to the maximum possible length.
>> +
>> +MTE CPU Property
>> +================
>> +
>> +The ``mte`` property controls the Memory Tagging Extension. For TCG, it
>> requires
>> +presence of tag memory (which can be turned on for the ``virt`` machine via
>> +``mte=on``). For KVM, it requires the ``KVM_CAP_ARM_MTE`` capability; until
>> +proper migration support is implemented, enabling MTE will install a
>> migration
>> +blocker.
>> +
>> +If not specified explicitly via ``on`` or ``off``, MTE will be available
>> +according to the following rules:
>> +
>> +* When TCG is used, MTE will be available iff tag memory is available; i.e.
>> it
>> + preserves the behaviour prior to introduction of the feature.
>> +
>> +* When KVM is used, MTE will default to off, so that migration will not
>> + unintentionally be blocked.
>> +
>> +* Other accelerators currently don't support MTE.
>
> Minor nits for the documentation:
> we should expand out "if and only if" -- not everybody recognizes
> "iff", especially if they're not native English speakers or not
> mathematicians.
Ok, will change that.
>
> Should we write specifically that in a future QEMU version KVM
> might change to defaulting to "on if available" when migration
> support is implemented?
I can certainly add "Future QEMU versions might change that behaviour."
We should be able to add compat handling for that.
Re: [PATCH v4 1/2] arm/kvm: add support for MTE, Richard Henderson, 2023/01/17
Re: [PATCH v4 1/2] arm/kvm: add support for MTE, Eric Auger, 2023/01/23
[PATCH v4 2/2] qtests/arm: add some mte tests, Cornelia Huck, 2023/01/11