Merge branch 'Enable-virtio_net-to-act-as-a-standby-for-a-passthru-device'

Sridhar Samudrala says:

====================
Enable virtio_net to act as a standby for a passthru device

The main motivation for this patch is to enable cloud service providers
to provide an accelerated datapath to virtio-net enabled VMs in a
transparent manner with no/minimal guest userspace changes. This also
enables hypervisor controlled live migration to be supported with VMs that
have direct attached SR-IOV VF devices.

Patch 1 introduces a failover module that provides a generic interface for
paravirtual drivers to listen for netdev register/unregister/link change
events from pci ethernet devices with the same MAC and takeover their
datapath. The notifier and event handling code is based on the existing
netvsc implementation.

Patch 2 refactors netvsc to use the registration/notification framework
introduced by failover module.

Patch 3 introduces a net_failover driver that provides an automated
failover mechanism to paravirtual drivers via APIs to create and destroy
a failover master netdev and mananges a primary and standby slave netdevs
that get registered via the generic failover infrastructure.

Patch 4 introduces a new feature bit VIRTIO_NET_F_STANDBY to virtio-net
that can be used by hypervisor to indicate that virtio_net interface
should act as a standby for another device with the same MAC address.

Patch 5 extends virtio_net to use alternate datapath when available and
registered. When STANDBY feature is enabled, virtio_net driver uese the
net_failover API to create an additional 'failover' netdev that acts as
a master device and controls 2 slave devices.  The original virtio_net
netdev is registered as 'standby' netdev and a passthru/vf device with
the same MAC gets registered as 'primary' netdev. Both 'standby' and
'failover' netdevs are associated with the same 'pci' device.  The user
accesses the network interface via 'failover' netdev. The 'failover'
netdev chooses 'primary' netdev as default for transmits when it is
available with link up and running.

As this patch series is initially focusing on usecases where hypervisor
fully controls the VM networking and the guest is not expected to directly
configure any hardware settings, it doesn't expose all the ndo/ethtool ops
that are supported by virtio_net at this time. To support additional usecases,
it should be possible to enable additional ops later by caching the state
in failover netdev and replaying when the 'primary' netdev gets registered.

At the time of live migration, the hypervisor needs to unplug the VF device
from the guest on the source host and reset the MAC filter of the VF to
initiate failover of datapath to virtio before starting the migration. After
the migration is completed, the destination hypervisor sets the MAC filter
on the VF and plugs it back to the guest to switch over to VF datapath.

This patch is based on the discussion initiated by Jesse on this thread.
https://marc.info/?l=linux-virtualization&m=151189725224231&w=2



v12:
- Tested live migration with virtio-net/AVF(i40evf) configured in failover
  mode while running iperf in background. Tried static ip and dhcp
  configurations using 'network' scripts and Network Manager.
- Build tested netvsc module.
Updates:
- Extended generic failover module to do common functions like setting
  FAILOVER_SLAVE flag, registering rx-handler and linking to upper dev in
  the generic register/unregister handlers.
  This required adding 3 additional failover ops pre_register, pre_unregister
  and handle_frame.  netvsc and net_failover drivers are updated to support
  these ops.

v11:
- Split net_failover module into 2 components.
  1. 'failover' module that provides generic failover infrastructure
  to register a failover instance and listen for slave events.
  2. 'net_failover' driver that provides APIs to create/destroy upper
  netdev and supports 3-netdev model used by virtio-net.
- Added documentation

v10:
- fix net_failover_open() to update failover CARRIER correctly based on
  standby and primary states.
- fix net_failover_handle_frame() to handle frames received on standby
  when primary is present.
- replace netdev_upper_dev_link with netdev_master_upper_dev_link and
  handle lower dev state changes.
- fix net_failver_create() and net_failover_register() interfaces to
  use ERR_PTR and avoid arg **
- disable setting mac address when virtio-net in STANDBY mode
- document exported symbols
- added entry to MAINTAINERS file

v9:
Select NET_FAILOVER automatically when VIRTIO_NET/HYPERV_NET
are enabled. (stephen)

v8:
- Made the failover managment routines more robust by updating the feature
  bits/other fields in the failover netdev when slave netdevs are
  registered/unregistered. (mst)
- added support for handling vlans.
- Limited the changes in netvsc to only use the notifier/event/lookups
  from the failover module. The slave register/unregister/link-change
  handlers are only updated to use the getbymac routine to get the
  upper netdev. There is no change in their functionality. (stephen)
- renamed structs/function/file names to use net_failover prefix. (mst)

v7
- Rename 'bypass/active/backup' terminology with 'failover/primary/standy'
  (jiri, mst)
- re-arranged dev_open() and dev_set_mtu() calls in the register routines
  so that they don't get called for 2-netdev model. (stephen)
- fixed select_queue() routine to do queue selection based on VF if it is
  registered as primary. (stephen)
-  minor bugfixes

v6 RFC:
  Simplified virtio_net changes by moving all the ndo_ops of the
  bypass_netdev and create/destroy of bypass_netdev to 'bypass' module.
  avoided 2 phase registration(driver + instances).
  introduced IFF_BYPASS/IFF_BYPASS_SLAVE dev->priv_flags
  replaced mutex with a spinlock

v5 RFC:
  Based on Jiri's comments, moved the common functionality to a 'bypass'
  module so that the same notifier and event handlers to handle child
  register/unregister/link change events can be shared between virtio_net
  and netvsc.
  Improved error handling based on Siwei's comments.
v4:
- Based on the review comments on the v3 version of the RFC patch and
  Jakub's suggestion for the naming issue with 3 netdev solution,
  proposed 3 netdev in-driver bonding solution for virtio-net.
v3 RFC:
- Introduced 3 netdev model and pointed out a couple of issues with
  that model and proposed 2 netdev model to avoid these issues.
- Removed broadcast/multicast optimization and only use virtio as
  backup path when VF is unplugged.
v2 RFC:
- Changed VIRTIO_NET_F_MASTER to VIRTIO_NET_F_BACKUP (mst)
- made a small change to the virtio-net xmit path to only use VF datapath
  for unicasts. Broadcasts/multicasts use virtio datapath. This avoids
  east-west broadcasts to go over the PCI link.
- added suppport for the feature bit in qemu
====================

Acked-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>