Re: [PATCH 0/4] RfC: microvm: add second ioapic

[Gerd Hoffmann <kraxel@redhat.com>]

On Fri, Oct 16, 2020 at 03:16:20PM +0200, Philippe Mathieu-Daudé wrote:
> On 10/16/20 1:43 PM, Gerd Hoffmann wrote:
> > Add a second ioapic to microvm.  Gives us more IRQ lines we can
> > use for virtio-mmio devices.  Bump number of possible virtio-mmio
> > devices from 8 to 24.
> > 
> > Gerd Hoffmann (4):
> >    microvm: make number of virtio transports runtime configurable
> >    microvm: make pcie irq base runtime configurable
> >    microvm: add second ioapic
> >    microvm: reconfigure irqs if second ioapic is available
> 
> After looking at Laurent's m68k virt machine,
> I wonder if it is possible to use the Goldfish-PIC
> with the MicroVM instead (or another Goldfish machine
> type).

/me updates the WIP microvm blog post ;)

Problem with goldfish is that it tries to drag over stuff from the arm
world to x86.  Specifically device trees.  On arm this works reasonable
well meanwhile.  Firmware and bootloaders have support for using device
trees and passing them on in the boot chain, so the linux kernel has a
device tree which it can use to figure which hardware is present on the
system.

On x86 this doesn't work at all, so you'll end up building a custom
kernel for the goldfish platform.  A stock distro kernel is not going
to work.

I'm to driving microvm the opposite direction:  Add acpi support.  That
is the standard x86 way to do hardware discovery (for hardware you can't
detect in other ways like pci devices).  Which in turn allows us to drop
microvm-specific quirks (like adding virtio-mmio devices to the kernel
command line) when booting linux.

So, for microvm this is not going to happen.  But feel free to add a
goldfish machine type if you want play with that.  The microvm merge
also cleaned up the x86 code base which in turn should make this
relatively easy now.

take care,
  Gerd