Re: [PATCH v6 1/2] arm/kvm: add support for MTE

[Peter Maydell]

On Tue, 28 Feb 2023 at 15:02, 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               | 110 +++++++++++++++++++++++++++++++
>  target/arm/internals.h           |   1 +
>  target/arm/kvm.c                 |  29 ++++++++
>  target/arm/kvm64.c               |   5 ++
>  target/arm/kvm_arm.h             |  19 ++++++
>  target/arm/monitor.c             |   1 +
>  10 files changed, 194 insertions(+), 13 deletions(-)



> +static inline bool arm_machine_has_tag_memory(void)
> +{
> +#ifndef CONFIG_USER_ONLY
> +    Object *obj = object_dynamic_cast(qdev_get_machine(), TYPE_VIRT_MACHINE);
> +
> +    /* so far, only the virt machine has support for tag memory */
> +    if (obj) {
> +        VirtMachineState *vms = VIRT_MACHINE(obj);
> +
> +        return vms->mte;
> +    }

Code inside target/arm shouldn't be fishing around inside
the details of the board model like this. For TCG I think that
at this point (i.e. at realize) you should be able to tell if
the board has set up tag memory, because it will have set
cpu->tag_memory to non-NULL.

thanks
-- PMM