[RFC PATCH] arm64: KVM: Allow userspace to configure guest MPIDR_EL1

[Andrew Jones]

On Wed, Apr 20, 2016 at 06:33:54PM +0100, Marc Zyngier wrote:
> On Wed, 20 Apr 2016 07:08:39 -0700
> Ashok Kumar <ashoks at broadcom.com> wrote:
> 
> > For guests with NUMA configuration, Node ID needs to
> > be recorded in the respective affinity byte of MPIDR_EL1.
> 
> As others have said before, the mapping between the NUMA hierarchy and
> MPIDR_EL1 are completely arbitrary, and only the firmware description
> can help the kernel in interpreting the affinity levels.
> 
> If you want any patch like this one to be considered, I'd like to see
> the corresponding userspace that:
> 
> - programs the affinity into the vcpus,

I have a start on this for QEMU that I can dust off and send as an RFC
soon.

> - pins the vcpus to specific physical CPUs,

This wouldn't be part of the userspace directly interacting with KVM,
but rather a higher level (even higher than libvirt, e.g.
openstack/ovirt). I also don't think we should need to worry about
which/how the phyiscal cpus get chosen. Let's assume that entity
knows how to best map the guest's virtual topology to a physical one.

> - exposes the corresponding firmware description (either DT or ACPI) to
>   the kernel.

The QEMU patches I've started on already generate the DT (the cpu-map
node). I started looking into how to do it for ACPI too, but there
were some questions about whether or not the topology description
tables added to the 6.1 spec were sufficient. I can send the DT part
soon, and continue to look into the ACPI part later though.

Thanks,
drew