Re: VirtIO MMIO for amd64

["Jonathan A. Kollasch" <jakllsch%kollasch.net@localhost>]

On Wed, Feb 23, 2022 at 12:28:36PM +0200, el16095 wrote:
> I've been working on a NetBSD-based unikernel and trying to make it
> compatible with the Firecracker VMM. Seeing as Firecracker only supports the
> MMIO transport method for VirtIO, I wanted to implement MMIO support for my
> unikernel.
> 
> I've seen that newer versions of NetBSD than what my source code was using
> have code for MMIO and specifically that Virtio MMIO support was implemented
> for ARM in NetBSD 9.0. So, what I want to ask is there similar support for
> amd64 also and if not are there some basics I could imitate from how it was
> implemented for ARM to get it working for amd64 also? Alternatively, is
> there any reading material you can suggest that explains how the device
> system works in NetBSD, so that I might possibly understand what changes
> would be needed by myself?

There shouldn't be anything preventing our existing Virtio MMIO via ACPI
code from working on amd64 in -current.  Probably just needs enabling
and testing. 

The "virtio* at acpi?" attachment is not currently included in the i386
or amd64 GENERIC kernels however.

I don't even know that Firecracker informs the guest about Virtio
MMIO devices via ACPI (or FDT).  If not, you'll need to create glue code
similar to virtio_acpi.c or virtio_mmio_fdt.c.