Date:   Fri, 27 Apr 2018 19:45:23 +0200
From:   Jiri Pirko <jiri@...nulli.us>
To:     Sridhar Samudrala <sridhar.samudrala@...el.com>
Cc:     mst@...hat.com, stephen@...workplumber.org, davem@...emloft.net,
        netdev@...r.kernel.org, virtualization@...ts.linux-foundation.org,
        virtio-dev@...ts.oasis-open.org, jesse.brandeburg@...el.com,
        alexander.h.duyck@...el.com, kubakici@...pl, jasowang@...hat.com,
        loseweigh@...il.com, aaron.f.brown@...el.com
Subject: Re: [PATCH net-next v9 0/4] Enable virtio_net to act as a standby
 for a passthru device

Fri, Apr 27, 2018 at 07:06:56PM CEST, sridhar.samudrala@...el.com wrote:
>v9:
>Select NET_FAILOVER automatically when VIRTIO_NET/HYPERV_NET 
>are enabled. (stephen)
>
>Tested live migration with virtio-net/AVF(i40evf) configured in 
>failover mode while running iperf in background.
>Build tested netvsc module.
>
>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 new feature bit VIRTIO_NET_F_STANDBY 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 2 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. It provides 2 sets of interfaces to paravirtual 
>drivers to support 2-netdev(netvsc) and 3-netdev(virtio_net) models.
>
>Patch 3 extends virtio_net to use alternate datapath when available and
>registered. When STANDBY feature is enabled, virtio_net driver creates
>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 'primary' 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.
>
>Patch 4 refactors netvsc to use the registration/notification framework
>supported by failover module.
>
>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 virtio netdev and replaying when the 'primary' netdev gets registered. 
> 
>The hypervisor needs to enable only one datapath at any time so that packets
>don't get looped back to the VM over the other datapath. When a VF is
>plugged, the virtio datapath link state can be marked as down.
>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


No changes in v9?


>
>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
>
>Sridhar Samudrala (4):
>  virtio_net: Introduce VIRTIO_NET_F_STANDBY feature bit
>  net: Introduce generic failover module
>  virtio_net: Extend virtio to use VF datapath when available
>  netvsc: refactor notifier/event handling code to use the failover
>    framework
>
> drivers/net/Kconfig             |   1 +
> drivers/net/hyperv/Kconfig      |   1 +
> drivers/net/hyperv/hyperv_net.h |   2 +
> drivers/net/hyperv/netvsc_drv.c | 134 ++----
> drivers/net/virtio_net.c        |  37 +-
> include/linux/netdevice.h       |  16 +
> include/net/net_failover.h      |  62 +++
> include/uapi/linux/virtio_net.h |   3 +
> net/Kconfig                     |  10 +
> net/core/Makefile               |   1 +
> net/core/net_failover.c         | 892 ++++++++++++++++++++++++++++++++++++++++
> 11 files changed, 1046 insertions(+), 113 deletions(-)
> create mode 100644 include/net/net_failover.h
> create mode 100644 net/core/net_failover.c
>
>-- 
>2.14.3

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