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

[Andrea Bolognani]

On Wed, Mar 01, 2023 at 11:17:40AM +0100, Cornelia Huck wrote:
> On Tue, Feb 28 2023, Andrea Bolognani <abologna@redhat.com> wrote:
> > On Tue, Feb 28, 2023 at 04:02:15PM +0100, Cornelia Huck wrote:
> >> +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.
> >
> > Is it okay to use -machine virt,mte=on unconditionally for both KVM
> > and TCG guests when MTE support is requested, or will that not work
> > for the former?
>
> QEMU will error out if you try this with KVM (basically, same behaviour
> as before.) Is that a problem for libvirt, or merely a bit inconvinient?

I'm actually a bit confused. The documentation for the mte property
of the virt machine type says

  mte
    Set on/off to enable/disable emulating a guest CPU which implements
    the Arm Memory Tagging Extensions. The default is off.

So why is there a need to have a CPU property in addition to the
existing machine type property?

>From the libvirt integration point of view, setting the machine type
property only for TCG is not a problem.

-- 
Andrea Bolognani / Red Hat / Virtualization