Re: [PATCH RFC 0/2] arm: enable MTE for QEMU + kvm

[Cornelia Huck <cohuck@redhat.com>]

On Fri, Jun 10 2022, Eric Auger <eauger@redhat.com> wrote:

> Hi Connie,
>
> On 5/12/22 15:11, Cornelia Huck wrote:
>> This series enables MTE for kvm guests, if the kernel supports it.
>> Lightly tested while running under the simulator (the arm64/mte/
>> kselftests pass... if you wait patiently :)
>> 
>> A new cpu property "mte" (defaulting to on if possible) is introduced;
>> for tcg, you still need to enable mte at the machine as well.
> isn't the property set to off by default when kvm is enabled (because of
> the migration blocker).

Oh, I had changed that around several times, and it seems I ended up
being confused when I wrote this cover letter... I wonder what the best
state would be (assuming that I don't manage to implement it soonish,
but it seems we still would need kernel changes as by the discussion in
that other patch series.)

>
> Eric
>> 
>> I've hacked up some very basic qtests; not entirely sure if I'm going
>> about it the right way.
>> 
>> Some things to look out for:
>> - Migration is not (yet) supported. I added a migration blocker if we
>>   enable mte in the kvm case. AFAIK, there isn't any hardware available
>>   yet that allows mte + kvm to be used (I think the latest Gravitons
>>   implement mte, but no bare metal instances seem to be available), so
>>   that should not have any impact on real world usage.
>> - I'm not at all sure about the interaction between the virt machine 'mte'
>>   prop and the cpu 'mte' prop. To keep things working with tcg as before,
>>   a not-specified mte for the cpu should simply give us a guest without
>>   mte if it wasn't specified for the machine. However, mte on the cpu
>>   without mte on the machine should probably generate an error, but I'm not
>>   sure how to detect that without breaking the silent downgrade to preserve
>>   existing behaviour.
>> - As I'm still new to arm, please don't assume that I know what I'm doing :)
>> 
>> 
>> Cornelia Huck (2):
>>   arm/kvm: enable MTE if available
>>   qtests/arm: add some mte tests
>> 
>>  target/arm/cpu.c               | 18 +++-----
>>  target/arm/cpu.h               |  4 ++
>>  target/arm/cpu64.c             | 78 ++++++++++++++++++++++++++++++++++
>>  target/arm/kvm64.c             |  5 +++
>>  target/arm/kvm_arm.h           | 12 ++++++
>>  target/arm/monitor.c           |  1 +
>>  tests/qtest/arm-cpu-features.c | 31 ++++++++++++++
>>  7 files changed, 137 insertions(+), 12 deletions(-)
>>