Re: [Qemu-devel] [opnfv-tech-discuss] rfc: vhost user enhancements for vm2vm communication

[Zhang, Yang Z]

Claudio Fontana wrote on 2015-09-07:
> Coming late to the party,
> 
> On 31.08.2015 16:11, Michael S. Tsirkin wrote:
>> Hello!
>> During the KVM forum, we discussed supporting virtio on top
>> of ivshmem. I have considered it, and came up with an alternative
>> that has several advantages over that - please see below.
>> Comments welcome.
> 
> as Jan mentioned we actually discussed a virtio-shmem device which would
> incorporate the advantages of ivshmem (so no need for a separate ivshmem
> device), which would use the well known virtio interface, taking advantage of
> the new virtio-1 virtqueue layout to split r/w and read-only rings as seen 
> from
> the two sides, and make use also of BAR0 which has been freed up for use by
> the device.

Interesting! Can you elaborate it? 

> 
> This way it would be possible to share the rings and the actual memory
> for the buffers in the PCI bars. The guest VMs could decide to use the
> shared memory regions directly as prepared by the hypervisor (in the

"the shared memory regions" here means share another VM's memory or like 
ivshmem?

> jailhouse case) or QEMU/KVM, or perform their own validation on the
> input depending on the use case.
> 
> Of course the communication between VMs needs in this case to be
> pre-configured and is quite static (which is actually beneficial in our use 
> case).

pre-configured means user knows which VMs will talk to each other and configure 
it when booting guest(i.e. in Qemu command line)?

> 
> But still in your proposed solution, each VM needs to be pre-configured to
> communicate with a specific other VM using a separate device right?
> 
> But I wonder if we are addressing the same problem.. in your case you are
> looking at having a shared memory pool for all VMs potentially visible to all 
> VMs
> (the vhost-user case), while in the virtio-shmem proposal we discussed we
> were assuming specific different regions for every channel.
> 
> Ciao,
> 
> Claudio
> 
> 
>


Best regards,
Yang