Re: [Qemu-devel] [virtio-dev] [PATCH v3 0/7] Vhost-pci for inter-VM communication

[Michael S. Tsirkin]

On Wed, Dec 13, 2017 at 12:35:21PM +0000, Stefan Hajnoczi wrote:
> I'm not saying that DPDK should use libvhost-user.  I'm saying that it's
> easy to add vfio vhost-pci support (for the PCI adapter I described) to
> DPDK.  This patch series would require writing a completely new slave
> for vhost-pci because the device interface is so different from
> vhost-user.

The main question is how appropriate is the vhost user protocol
for passing to guests. And I am not sure at this point.

Someone should go over vhost user messages and see whether they are safe
to pass to guest. If most are then we can try the transparent approach.
If most aren't then we can't and might as well use the proposed protocol
which at least has code behind it.

I took a quick look and I doubt we can do something that is both
compatible with the existing vhost-user and will make it possible to
extend the protocol without qemu changes. Let's assume I pass a new
message over the vhost-user channel.  How do we know it's safe to pass
it to the guest?

That's why we gate any protocol change on a feature bit and must parse
all messages.

Cc Maxime as well.