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Date:   Mon, 20 May 2019 16:44:31 +0200
From:   Stefano Garzarella <>
To:     Dexuan Cui <>
Cc:     "" <>,
        Stefan Hajnoczi <>,
        Jorgen Hansen <>,
        "David S. Miller" <>,
        Vishnu Dasa <>,
        KY Srinivasan <>,
        Haiyang Zhang <>,
        Stephen Hemminger <>,
        Sasha Levin <>
Subject: Re: [RFC] vsock: proposal to support multiple transports at runtime

Hi Dexuan,

On Thu, May 16, 2019 at 09:48:11PM +0000, Dexuan Cui wrote:
> > From: Stefano Garzarella <>
> > Sent: Tuesday, May 14, 2019 1:16 AM
> > To:; Stefan Hajnoczi <>; Dexuan
> > 
> > Hi guys,
> > I'm currently interested on implement a multi-transport support for VSOCK in
> > order to handle nested VMs.
> Hi Stefano,
> Thanks for reviving the discussion! :-)

You're welcome :)

> I don't know a lot about the details of kvm/vmware sockets, but please let me
> share my understanding about them, and let me also share some details about
> hyper-v sockets, which I think should be the simplest:
> 1) For hyper-v sockets, the "host" can only be Windows. We can do nothing on the
> Windows host, and I guess we need to do nothing there.

I agree that for the Windows host we shouldn't change anything.

> 2) For hyper-v sockets, I think we only care about Linux guest, and the guest can
> only talk to the host; a guest can not talk to another guest running on the same host.

Also for KVM (virtio) a guest can talk only with the host.

> 3) On a hyper-v host, if the guest is running kvm/vmware (i.e. nested virtualization),
> I think in the "KVM guest" the Linux hyper-v transport driver needs to load so that
> the guest can talk to the host (I'm not sure about "vmware guest" in this case); 
> the "KVM guest" also needs to load the kvm transport drivers so that it can talk
> to its child VMs (I'm not sure abut "vmware guest" in this case).

Okay, so since in the "KVM guest" we will have both hyper-v and kvm
transports, we should implement a way to decide what transport use in
the cases that I described in the first email.

> 4) On kvm/vmware, if the guest is a Windows guest, I think we can do nothing in
> the guest;

Yes, the driver in Windows guest shouldn't change.

> if the guest is Linux guest, I think the kvm/vmware transport drivers
> should load; if the Linux guest is running kvm/vmware (nested virtualization), I
> think the proper "to child VMs" versions of the kvm/vmware transport drivers
> need to load.

Exactly, and for the KVM side is the vhost-vsock driver. So, as the
point 3, we should support at least two transports running in Linux at
the same time.

Thank you very much to share these information!


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