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

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Message-ID: <20201202133754.2ek2wgutkujkvxaf@steredhat>
Date:   Wed, 2 Dec 2020 14:37:54 +0100
From:   Stefano Garzarella <sgarzare@...hat.com>
To:     Andra Paraschiv <andraprs@...zon.com>
Cc:     netdev <netdev@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        "David S . Miller" <davem@...emloft.net>,
        David Duncan <davdunc@...zon.com>,
        Dexuan Cui <decui@...rosoft.com>,
        Alexander Graf <graf@...zon.de>,
        Jorgen Hansen <jhansen@...are.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Stefan Hajnoczi <stefanha@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>
Subject: Re: [PATCH net-next v1 0/3] vsock: Add flag field in the vsock
 address

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