Re: [PATCH net-next v1 0/3] vsock: Add flag field in the vsock address

[Stefano Garzarella]

Hi Andra,

On Tue, Dec 01, 2020 at 05:25:02PM +0200, Andra Paraschiv wrote:
> vsock enables communication between virtual machines and the host they are
> running on. Nested VMs can be setup to use vsock channels, as the multi
> transport support has been available in the mainline since the v5.5 Linux kernel
> has been released.
>
> Implicitly, if no host->guest vsock transport is loaded, all the vsock packets
> are forwarded to the host. This behavior can be used to setup communication
> channels between sibling VMs that are running on the same host. One example can
> be the vsock channels that can be established within AWS Nitro Enclaves
> (see Documentation/virt/ne_overview.rst).
>
> To be able to explicitly mark a connection as being used for a certain use case,
> add a flag field in the vsock address data structure. The "svm_reserved1" field
> has been repurposed to be the flag field. The value of the flag will then be
> taken into consideration when the vsock transport is assigned.
>
> This way can distinguish between nested VMs / local communication and sibling
> VMs use cases. And can also setup one or more types of communication at the same
> time.

Another thing worth mentioning is that for now it is not supported in 
vhost-vsock, since we are discarding every packet not addressed to the 
host.

What we should do would be:
- add a new IOCTL to vhost-vsock to enable sibling communication, by 
  default I'd like to leave it disabled

- allow sibling forwarding only if both guests have sibling 
  communication enabled and we should implement some kind of filtering 
  or network namespace support to allow the communication only between a 
  subset of VMs


Do you have plans to work on it?

Otherwise I put it in my to-do list and hope I have time to do it (maybe 
next month).

Thanks,
Stefano