Date:   Mon, 19 Aug 2019 14:09:11 +0100
From:   Stefan Hajnoczi <stefanha@...hat.com>
To:     Stefano Garzarella <sgarzare@...hat.com>
Cc:     netdev@...r.kernel.org, Dexuan Cui <decui@...rosoft.com>,
        Jorgen Hansen <jhansen@...are.com>,
        "David S. Miller" <davem@...emloft.net>,
        Vishnu Dasa <vdasa@...are.com>,
        "K. Y. Srinivasan" <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        Sasha Levin <sashal@...nel.org>
Subject: Re: [RFC v2] vsock: proposal to support multiple transports at
 runtime

On Thu, Jun 06, 2019 at 12:09:12PM +0200, Stefano Garzarella wrote:
> 
> Hi all,
> this is a v2 of a proposal addressing the comments made by Dexuan, Stefan,
> and Jorgen.
> 
> v1: https://www.spinics.net/lists/netdev/msg570274.html
> 
> 
> 
> We can define two types of transport that we have to handle at the same time
> (e.g. in a nested VM we would have both types of transport running together):
> 
> - 'host->guest' transport, it runs in the host and it is used to communicate
>   with the guests of a specific hypervisor (KVM, VMWare or Hyper-V). It also
>   runs in the guest who has nested guests, to communicate with them.
> 
>   [Phase 2]
>   We can support multiple 'host->guest' transport running at the same time,
>   but on x86 only one hypervisor uses VMX at any given time.
> 
> - 'guest->host' transport, it runs in the guest and it is used to communicate
>   with the host.
> 
> 
> The main goal is to find a way to decide what transport use in these cases:
> 1. connect() / sendto()
> 
>    a. use the 'host->guest' transport, if the destination is the guest
>       (dest_cid > VMADDR_CID_HOST).
> 
>       [Phase 2]
>       In order to support multiple 'host->guest' transports running at the same
>       time, we should assign CIDs uniquely across all transports. In this way,
>       a packet generated by the host side will get directed to the appropriate
>       transport based on the CID.
> 
>    b. use the 'guest->host' transport, if the destination is the host or the
>       hypervisor.
>       (dest_cid == VMADDR_CID_HOST || dest_cid == VMADDR_CID_HYPERVISOR)
> 
> 
> 2. listen() / recvfrom()
> 
>    a. use the 'host->guest' transport, if the socket is bound to
>       VMADDR_CID_HOST, or it is bound to VMADDR_CID_ANY and there is no
>       'guest->host' transport.
>       We could also define a new VMADDR_CID_LISTEN_FROM_GUEST in order to
>       address this case.
> 
>       [Phase 2]
>       We can support network namespaces to create independent AF_VSOCK
>       addressing domains:
>       - could be used to partition VMs between hypervisors or at a finer
>    	 granularity;
>       - could be used to isolate host applications from guest applications
>    	 using the same ports with CID_ANY;
> 
>    b. use the 'guest->host' transport, if the socket is bound to local CID
>       different from the VMADDR_CID_HOST (guest CID get with
>       IOCTL_VM_SOCKETS_GET_LOCAL_CID), or it is bound to VMADDR_CID_ANY (to be
>       backward compatible).
>       Also in this case, we could define a new VMADDR_CID_LISTEN_FROM_HOST.
> 
>    c. shared port space between transports
>       For incoming requests or packets, we should be able to choose which
>       transport use, looking at the 'port' requested.
> 
>       - stream sockets already support shared port space between transports
>         (one port can be assigned to only one transport)
> 
>       [Phase 2]
>       - datagram sockets will support it, but for now VMCI transport is the
>         default transport for any host side datagram socket (KVM and Hyper-V
>         do not yet support datagrams sockets)
> 
> We will make the loading of af_vsock.ko independent of the transports to
> allow to:
>    - create a AF_VSOCK socket without any loaded transports;
>    - listen on a socket (e.g. bound to VMADDR_CID_ANY) without any loaded
>      transports;
> 
> Hopefully, we could move MODULE_ALIAS_NETPROTO(PF_VSOCK) from the
> vmci_transport.ko to the af_vsock.ko.
> [Jorgen will check if this will impact the existing VMware products]
> 
> Notes:
>    - For Hyper-V sockets, the host can only be Windows. No changes should
>      be required on the Windows host to support the changes on this proposal.
> 
>    - Communication between guests are not allowed on any transports, so we can
>      drop packets sent from a guest to another guest (dest_cid >
>      VMADDR_CID_HOST) if the 'host->guest' transport is not available.
> 
>    - [Phase 2] tag used to identify things that can be done at a later stage,
>      but that should be taken into account during this design.
> 
>    - Namespace support will be developed in [Phase 2] or in a separate project.
> 
> 
> 
> Comments and suggestions are welcome.
> I'll be on PTO for next two weeks, so sorry in advance if I'll answer later.
> 
> If we agree on this proposal, when I get back, I'll start working on the code
> to get a first PATCH RFC.

Stefano,
I've reviewed your proposal and it looks good for solving nested
virtualization.

The tricky implementation details will be supporting listen sockets,
especially with VMADDR_CID_ANY so they can be accessed from both
transports.

Stefan

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