Re: [Qemu-devel] [PATCH 0/4] add failover feature for assigned network devices

[si-wei liu <si-wei.liu@oracle.com>]

On 5/21/2019 11:49 AM, Jens Freimann wrote:
> On Tue, May 21, 2019 at 07:37:19AM -0400, Michael S. Tsirkin wrote:
>> On Tue, May 21, 2019 at 09:21:57AM +0200, Jens Freimann wrote:
>>> On Mon, May 20, 2019 at 04:56:57PM -0600, Alex Williamson wrote:
>>> > On Fri, 17 May 2019 14:58:16 +0200
>>> > Jens Freimann <jfreimann@redhat.com> wrote:
>>> > > Command line example:
>>> > >
>>> > > qemu-system-x86_64 -enable-kvm -m 3072 -smp 3 \
>>> > >         -machine q35,kernel-irqchip=split -cpu host   \
>>> > >         -k fr   \
>>> > >         -serial stdio   \
>>> > >         -net none \
>>> > >         -qmp unix:/tmp/qmp.socket,server,nowait \
>>> > >         -monitor telnet:127.0.0.1:5555,server,nowait \
>>> > >         -device 
>>> pcie-root-port,id=root0,multifunction=on,chassis=0,addr=0xa \
>>> > >         -device pcie-root-port,id=root1,bus=pcie.0,chassis=1 \
>>> > >         -device pcie-root-port,id=root2,bus=pcie.0,chassis=2 \
>>> > >         -netdev 
>>> tap,script=/root/bin/bridge.sh,downscript=no,id=hostnet1,vhost=on \
>>> > >         -device 
>>> virtio-net-pci,netdev=hostnet1,id=net1,mac=52:54:00:6f:55:cc,bus=root2,failover=on 
>>> \
>>> > >         /root/rhel-guest-image-8.0-1781.x86_64.qcow2
>>> > >
>>> > > Then the primary device can be hotplugged via
>>> > >  (qemu) device_add 
>>> vfio-pci,host=5e:00.2,id=hostdev0,bus=root1,standby=net1
>>> >
>>> > Is this standby= option only valid for Network/Ethernet class code
>>> > devices?  If so, perhaps vfio-pci code should reject the option on 
>>> any
>>> > non-ethernet devices.  The option is also non-intuitive for users, 
>>> only
>>> > through examples like above can we see it relates to the id of the
>>> > secondary device.  Could we instead name it something like
>>> > "standby_net_failover_pair_id="?
>>>
>>> It is only for ethernet (VFs), I will add code to reject 
>>> non-ethernet VF devices.
>>> I agree the name is not descriptive and the one you suggest seems 
>>> good to
>>> me.
>>> >
>>> > Also, this feature requires matching MAC addresses per the 
>>> description,
>>> > where is that done?  Is it the user's responsibility to set the 
>>> MAC on
>>> > the host device prior to the device_add?  If so, is this actually not
>>> > only specific to ethernet devices, but ethernet VFs?
>>>
>>> Yes, it's the users responsibility and the MACs are then matched by
>>> the net_failover driver in the guest. It makes sense for ethernet 
>>> VFs only,
>>> I'll add a check for that.
>>
>> Actually is there a list of devices for which this has been tested
>> besides mlx5? I think someone said some old intel cards
>> don't support this well, we might need to blacklist these ...
>
> So far I've tested mlx5 and XL710 which both worked, but I'm
> working on testing with more devices. But of course help with testing
> is greatly appreciated.
It won't work on Intel ixgbe and Broadcom bnxt_en, which requires 
toggling the state of tap backing the virtio-net in order to 
release/reprogram MAC filter. Actually, it's very few NICs that could 
work with this - even some works by chance the behavior is undefined. 
Instead of blacklisting it makes more sense to whitelist the NIC that 
supports it - with some new sysfs attribute claiming the support 
presumably.

-Siwei

>
> regards,
> Jens