Re: [PATCH v4 0/8] Introduce the microvm machine type

[Paolo Bonzini]

On 25/09/19 11:12, Gerd Hoffmann wrote:
>   Hi,
> 
>> If you want to add hotplug to microvm, you can reuse the existing code
>> for CPU and memory hotplug controllers, and write drivers for them in
>> Linux's drivers/platform.  The drivers would basically do what the ACPI
>> AML tells the interpreter to do.
> 
> How would the linux kernel detect those devices?
>
> I guess that wouldn't be ACPI, seems everyone wants avoid it[1].
> 
> So device tree on x86?  Something else?

Yes, device tree would be great.

> [1] Not clear to me why, some minimal ACPI tables listing our
>     devices (isa-serial, fw_cfg, ...) doesn't look unreasonable
>     to me.

It's not, but ACPI is dog slow and half of the boot time is cut if you
remove it.

> We could also make virtio-mmio discoverable that way.

True, but the simplest way to plumb virtio-mmio into ACPI would be
taking the device tree properties and representing them as _DSD[1].  So
at this point it's just as easy to use directly the device tree.

Paolo

[1]
https://kernel-recipes.org/en/2015/talks/representing-device-tree-peripherals-in-acpi/