Re: How to create/use RPMSG-over-VIRTIO devices in Linux

[Jason Gunthorpe <jgg@ziepe.ca>]

On Mon, Sep 16, 2024 at 08:38:42AM -0500, Doug Miller wrote:
> On 9/15/2024 11:58 AM, Jason Gunthorpe wrote:
> > On Fri, Sep 13, 2024 at 08:39:26AM -0600, Mathieu Poirier wrote:
> > > KVM has nothing to do with this.  The life of a virtio device starts
> > > in the VMM (Virtual Machine Manager) where a backend device is created
> > > and a virtio MMIO entry for that device is added to the device tree
> > > that is fed to the VM kernel.  When the VM kernel boots the virtio
> > > MMIO entry in the DT is parsed as part of the normal device discovery
> > > process and a virtio-device is instantiated, added to the virtio-bus
> > > and a driver is probed.
> > > 
> > > I suggest you start looking at that process using the kvmtool and a
> > > simple virtio device such as virtio-rng.
> > I would repeat again, I think trying to create a companion virtio
> > device to go along with a real vPCI device and then logically
> > associating both of them with a single driver is going to cause so
> > much pain you should not do it.
> > 
> > Find a way to send your RPCs through your own vPCI device.
> 
> When you say "your own vPCI device", are you referring to the virtual
> functions that are created by the adapter? Those are defined by the
> hardware specification and we don't have the ability to extend them.

Yes you do the VMM can extend them. You need some qemu code or a
vfio-cornelis or something like that.

> What we're investigating is using RPMSG-over-VIRTIO, not using virtio
> devices directly. 

I understand, and that will be very painful.

Jason