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From: Stefano Garzarella <sgarzare@redhat.com>
To: Jorgen Hansen <jhansen@vmware.com>
Cc: "netdev@vger.kernel.org" <netdev@vger.kernel.org>,
	"Michael S. Tsirkin" <mst@redhat.com>,
	"kvm@vger.kernel.org" <kvm@vger.kernel.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Jason Wang <jasowang@redhat.com>,
	"David S. Miller" <davem@davemloft.net>,
	Dexuan Cui <decui@microsoft.com>,
	Haiyang Zhang <haiyangz@microsoft.com>,
	Sasha Levin <sashal@kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Arnd Bergmann <arnd@arndb.de>,
	Stefan Hajnoczi <stefanha@redhat.com>,
	"linux-hyperv@vger.kernel.org" <linux-hyperv@vger.kernel.org>,
	"K. Y. Srinivasan" <kys@microsoft.com>,
	Stephen Hemminger <sthemmin@microsoft.com>,
	"virtualization@lists.linux-foundation.org" 
	<virtualization@lists.linux-foundation.org>
Subject: Re: [PATCH net-next 11/14] vsock: add multi-transports support
Date: Wed, 13 Nov 2019 17:38:42 +0100
Message-ID: <20191113163842.6byl2qul4nbjf5no@steredhat> (raw)
In-Reply-To: <MWHPR05MB3376560CFD2A710723843828DA760@MWHPR05MB3376.namprd05.prod.outlook.com>

On Wed, Nov 13, 2019 at 02:30:24PM +0000, Jorgen Hansen wrote:
> > From: Stefano Garzarella [mailto:sgarzare@redhat.com]
> > Sent: Tuesday, November 12, 2019 11:37 AM
> 
> > > > > You already mentioned that you are working on a fix for loopback
> > > > > here for the guest, but presumably a host could also do loopback.
> > > >
> > > > IIUC we don't support loopback in the host, because in this case the
> > > > application will use the CID_HOST as address, but if we are in a nested
> > > > VM environment we are in trouble.
> > >
> > > If both src and dst CID are CID_HOST, we should be fairly sure that this
> > > Is host loopback, no? If src is anything else, we would do G2H.
> > >
> > 
> > The problem is that we don't know the src until we assign a transport
> > looking at the dst. (or if the user bound the socket to CID_HOST before
> > the connect(), but it is not very common)
> > 
> > So if we are in a L1 and the user uses the local guest CID, it works, but if
> > it uses the HOST_CID, the packet will go to the L0.
> > 
> > If we are in L0, it could be simple, because we can simply check if G2H
> > is not loaded, so any packet to CID_HOST, is host loopback.
> > 
> > I think that if the user uses the IOCTL_VM_SOCKETS_GET_LOCAL_CID, to set
> > the dest CID for the loopback, it works in both cases because we return the
> > HOST_CID in L0, and always the guest CID in L1, also if a H2G is loaded to
> > handle the L2.
> > 
> > Maybe we should document this in the man page.
> 
> Yeah, it seems like a good idea to flesh out the routing behavior for nested
> VMs in the man page.

I'll do it.

> 
> > 
> > But I have a question: Does vmci support the host loopback?
> > I've tried, and it seems not.
> 
> Only for datagrams - not for stream sockets.
>  

Ok, I'll leave the datagram loopback as before.

> > Also vhost-vsock doesn't support it, but virtio-vsock does.
> > 
> > > >
> > > > Since several people asked about this feature at the KVM Forum, I would
> > like
> > > > to add a new VMADDR_CID_LOCAL (i.e. using the reserved 1) and
> > implement
> > > > loopback in the core.
> > > >
> > > > What do you think?
> > >
> > > What kind of use cases are mentioned in the KVM forum for loopback?
> > One concern
> > > is that we have to maintain yet another interprocess communication
> > mechanism,
> > > even though other choices exist already  (and those are likely to be more
> > efficient
> > > given the development time and specific focus that went into those). To
> > me, the
> > > local connections are mainly useful as a way to sanity test the protocol and
> > transports.
> > > However, if loopback is compelling, it would make sense have it in the core,
> > since it
> > > shouldn't need a specific transport.
> > 
> > The common use cases is for developer point of view, and to test the
> > protocol and transports as you said.
> > 
> > People that are introducing VSOCK support in their projects, would like to
> > test them on their own PC without starting a VM.
> > 
> > The idea is to move the code to handle loopback from the virtio-vsock,
> > in the core, but in another series :-)
> 
> OK, that makes sense.

Thanks,
Stefano


  reply index

Thread overview: 46+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-10-23  9:55 [PATCH net-next 00/14] " Stefano Garzarella
2019-10-23  9:55 ` [PATCH net-next 01/14] vsock/vmci: remove unused VSOCK_DEFAULT_CONNECT_TIMEOUT Stefano Garzarella
2019-10-30 14:54   ` Jorgen Hansen
2019-10-23  9:55 ` [PATCH net-next 02/14] vsock: remove vm_sockets_get_local_cid() Stefano Garzarella
2019-10-30 14:55   ` Jorgen Hansen
2019-10-23  9:55 ` [PATCH net-next 03/14] vsock: remove include/linux/vm_sockets.h file Stefano Garzarella
2019-10-30 14:57   ` Jorgen Hansen
2019-10-23  9:55 ` [PATCH net-next 04/14] vsock: add 'transport' member in the struct vsock_sock Stefano Garzarella
2019-10-30 14:57   ` Jorgen Hansen
2019-10-23  9:55 ` [PATCH net-next 05/14] vsock/virtio: add transport parameter to the virtio_transport_reset_no_sock() Stefano Garzarella
2019-10-23  9:55 ` [PATCH net-next 06/14] vsock: add 'struct vsock_sock *' param to vsock_core_get_transport() Stefano Garzarella
2019-10-30 15:01   ` Jorgen Hansen
2019-10-23  9:55 ` [PATCH net-next 07/14] vsock: handle buffer_size sockopts in the core Stefano Garzarella
2019-10-27  8:08   ` Stefan Hajnoczi
2019-10-30 15:08   ` Jorgen Hansen
2019-10-31  8:50     ` Stefano Garzarella
2019-10-23  9:55 ` [PATCH net-next 08/14] vsock: add vsock_create_connected() called by transports Stefano Garzarella
2019-10-27  8:12   ` Stefan Hajnoczi
2019-10-30 15:12   ` Jorgen Hansen
2019-10-23  9:55 ` [PATCH net-next 09/14] vsock: move vsock_insert_unbound() in the vsock_create() Stefano Garzarella
2019-10-30 15:12   ` Jorgen Hansen
2019-10-23  9:55 ` [PATCH net-next 10/14] hv_sock: set VMADDR_CID_HOST in the hvs_remote_addr_init() Stefano Garzarella
2019-10-23  9:55 ` [PATCH net-next 11/14] vsock: add multi-transports support Stefano Garzarella
2019-10-23 15:08   ` Stefano Garzarella
2019-10-30 15:40     ` Jorgen Hansen
2019-10-31  8:54       ` Stefano Garzarella
2019-11-11 13:53   ` Jorgen Hansen
2019-11-11 17:17     ` Stefano Garzarella
2019-11-12  9:59       ` Jorgen Hansen
2019-11-12 10:36         ` Stefano Garzarella
2019-11-13 14:30           ` Jorgen Hansen
2019-11-13 16:38             ` Stefano Garzarella [this message]
2019-10-23  9:55 ` [PATCH net-next 12/14] vsock/vmci: register vmci_transport only when VMCI guest/host are active Stefano Garzarella
2019-10-27  8:17   ` Stefan Hajnoczi
2019-10-29 16:35     ` Stefano Garzarella
2019-11-04 10:10   ` Stefano Garzarella
2019-11-11 16:27   ` Jorgen Hansen
2019-11-11 17:30     ` Stefano Garzarella
2019-11-12 10:03       ` Jorgen Hansen
2019-11-12 10:42         ` Stefano Garzarella
2019-10-23  9:55 ` [PATCH net-next 13/14] vsock: prevent transport modules unloading Stefano Garzarella
2019-11-11 16:36   ` Jorgen Hansen
2019-10-23  9:55 ` [PATCH net-next 14/14] vsock: fix bind() behaviour taking care of CID Stefano Garzarella
2019-11-11 16:53   ` Jorgen Hansen
2019-10-27  8:01 ` [PATCH net-next 00/14] vsock: add multi-transports support Stefan Hajnoczi
2019-10-29 16:27   ` Stefano Garzarella

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